ALBERT

Notes: Aus der Reaktion der bekannten Methylenphosphane 1a-e mit Lithio-α-chlororganylen 2a, b erhält man in sehr guten Ausbeuten die Bismethylenphosphorane 3a-f. Die Verbindungen 3c-f sind die ersten gemischt substituierten Vertreter der λ5σ3-Bismethylenphosphorane, die mit Ausnahme von 3e, f isoliert werden können. Die Verbindungen 3e, f lagern in die neuen Phosphirane 6a, b um. Die Reaktion des Methylenphosphans 1b mit Diphenyldiazomethan (4) verläuft über ein spektroskopisch erfaßbares Dihydrodiazaphosphol 5 zum Produkt 3e. Die Reaktionsverläufe, die spektroskopischen Daten sowie die Röntgenstrukturen von 3d und 6a werden diskutiert.

Notes: Tricarbonyl[2-(η5-cyclopentadienyl)ethyl]molybdän (1) reagiert photochemisch mit 1,3-Butadien (2), (E)-1,3-Pentadien (3) bzw. 2-Methyl-1,3-butadien (4) zu den korrespondierenden η2- und η4-Dien-Komplexen. Stufenweise werden Dicarbonyl[2-(η5-cyclopentadienyl)ethyl](η2-dien)molybdän (5, 8, 11) und Carbonyl[2-(η5-cyclopentadienyl)ethyl](η4-dien)molybdän (6, 9, 12) gebildet. Insertion des 1,3-Butadiens in die Mo—C-σ-Bindung von 5 ergibt Dicarbonyl[6-(η5-cyclopentadienyl)-η3-(E)-2-hexenyl]molybdän (7) als Nebenprodukt. Gleichermaßen reagiert 8 zu dem entsprechenden [6-(η5-Cyclopentadienyl)-η3-(E,E)-1-methyl-2-hexenyl]-Chelatkomplex 10. Die η2-Dien-Liganden in 5, 8, 11 zeigen gehinderte Rotation um die Achse durch die Mitte der CC-Doppelbindung und das Zentralatom. Zwei unterschiedliche Rotamere können bei tiefen Temperaturen beobachtet werden. Die Energiebarrieren wurden durch Linienform-Analyse zu ΔG300≠ = 62.0 ± 0.2 kJ/mol für 5, ΔG280≠ = 66.2 ± 0.2 kJ/mol für 8 und ΔG298≠ = 61.0 ± 0.2 kJ/mol für 11 ermittelt. Komplex 9 ist in einer, 12 in beiden der zwei möglichen diastereomeren Formen erhältlich.

Notes: Die chinoide Titelverbindung 6 entsteht im Gleichgewicht zu 〉95% und kann isoliert werden, wenn die beiden Titelradikale 1 und 3 in Lösung erzeugt werden. Ursache hierfür ist die räumlich günstigere Unterbringung der sperrigen tBu-Gruppe am sp2-C-Atom der Methylengruppe. Die Struktur von 6 wird durch 1,5-H-Verschiebung zu 8 sowie dessen Autoxidation bei -10°C zu tBuOH und 4-Tritylbenzophenon (12) bewiesen. Synthesen analoger Verbindungen werden beschrieben.

Notes: The preparation of the (α-chloroallyl)boronate 4 of 92% e.e. is described. Its addition to achiral aldehydes resulted in the homoallyl alcohols 6 of 82-92% e.e. Cooperative diastereoface selectivity on addition of ent-4 to isopropylideneglyceraldehyde (22) gave the product 23 of high diastereomeric purity. Reagent control of stereoselectivity on addition of 4 to 22 resulted in 25 of 77% diastereomeric purity.

Notes: Reactions with Aziridines, 36 Arene Hydrides 2. SN2 and SET Reactions of N-Acylaziridines with Diphenylmethanide and „Naphthalene Hydride“ (Anion of Dihydronaphthalene)Diphenylmethane is incompletely deprotonated by sodium naphthalenide in THF so that some „naphthalene hydride“ 4 (anion of 1,4-dihydronaphthalene) remains present in the deprotonation equilibrium. The generated diphenylmethanide anion 3a reacts with the N-acylaziridines 6a-c to form the expected amidoethyl derivatives 7a-c in yields of less than 50%. The formation of by-products from 6b and 6c can be rationlized on the basis of classic ionic mechanisms. However, for 6a the by-product N-ethylbenzamide clearly points to a SET mechanism with „naphthalene hydride“ 4 as the electron source and with the radical 8 as a hydrogen source.

Notes: Die Effekte von Deuteriumatomen in den Positionen 1 und 4 von exo-6-Brom- (11) und endo-6-Methoxytricyclo[3.2.1.02,7]oct-3-en (12) sowie exo-4-Methoxybicyclo[3.2.1]octa-2,6-dien (13) auf deren 13C-chemische Verschiebungen stützen die frühere Interpretation der Effekte bei entsprechend deuterierten Bicyclo[3.2.1]octa-3,6-dien-2-yl-Anionen 1 und belegen so die homokonjugative Wechselwirkung in 1.  -  Ausgehend von Bicyclo[3.2.1]oct-6-en-3-on (14) und Bicyclo[3.1.0]hex-2-en-endo-6-carbaldehyd (17) stellte man 3-Phenyl- (16) bzw. endo-4-Phenyl-(19a) und exo-4-Phenylbicyclo[3.2.1]octa-2,6-dien (19b) dar. 2,4-Diphenylbicyclo[3.2.1]octa-2,6-dien (6) und 19a, b wurden mit Methyllithium bzw. n-Butyllithium, Tricyclo[6.3.1.02,7]dodeca-2,4,6,9-tetraen (4) sowie 16 mit Kalium-tert-butoxid/n-Butyllithium deprotoniert, wobei die entsprechenden Bicyclo[3.2.1]octa-3,6-dien-2-yl-Anionderivate 7, 21Li, 5 und 22 entstanden. Aus 19a, b wurde mit Kalium-tert-butoxid/n-Butyllithium auch 21K, d. h. das zugehörige Anion mit K+ als Gegenion erhalten. Die NMR-Spektren von 21Li erwiesen sich im Gegensatz zu jenen von 21K im Bereich von +45 bis -30°C als temperaturabhängig. Die 13C-NMR-Spektren der Anionen und der zugehörigen Kohlenwasserstoffe werden im Vergleich mit den Spektren der unsubstituierten Verbindungen 1 und 2 ausführlich diskutiert. Insbesondere die starken Variationen der chemischen Verschiebungen von C-6,7 in Abhängigkeit von den Substitutenten am Allylteil des Bicyclo[3.2.1]octa-3,6-dien-2-yl-Anionsystems bieten ein starkes Argument für die bishomoaromatische Natur dieser Anionen.

Notes: 3-Alkylquinolizinium Iodides from Metalated α-Picoline and 3-Ethoxyacroleins2-Alkylquinolizinium iodides 4 are obtained in good overall yields by treating lithiated 2-methylpyridine 1 with 2-alkyl-3-ethoxyacroleins 2. 3-Alkyl-4-ethoxy-1-(2-pyridyl)-3-buten-2-ols 3 are isolated as primary products which readily cyclize to give the title compounds 4 upon heating in aqueous hydrogen iodide.

Notes: Funktionell substituierte Vinylcarbanionen, 29. Reaktion einer β-lithiierten Acrylsäure mit Oxetanen als Electrophilβ-Lithiiertes β-(Ethylthio)acrylat 1A reagiert mit den Oxetanen 2 bzw. (±)-5 in Anwesenheit von Bortrifluorid-Ether zu den entsprechenden γ-hydroxypropyl-substituierten Derivaten 3 bzw. 6. Von den 2-Alkyl/phenyl-3-ethoxy-oxetanen (±)-5 reagieren die erythro-Derivate deutlich rascher als die threo-Derivate.

Notes: Die anodische Oxidation von ([Carbonyl-18O]Benzoyloxy)essigsäure (1b) an Graphitelektroden in Methanol liefert unter Erhaltung des markierten Sauerstoffs in der Carbonylposition das Substitutionsprodukt Benzoesäure-methoxymethylester (3) und das Fragmentierungsprodukt Benzoesäure-methylester (4). Damit wird die Beteiligung eines 1,3-Dioxetanylium-Ions 2′ an der Elektrolyse von O-benzoylierten α-Hydroxyessigsäuren ausgeschlossen. Die kationische Zwischenstufe 2 ist offenkettig.

Notes: New Syntheses of 2-Acylbenzofurans, 2-Acylindoles, 2-Indolylcarboxylates, and 2-Quinolones by Intramolecular Wittig ReactionThe title compounds are obtained by intramolecular Wittig reaction of 2-(α-ketoacyloxy)-, 2-(α-ketoacylamino)-, or 2-[(ω-alkoxycarbonylacyl)amino]benzyltriphenylphosphonium salts, respectively.

Notes: Bis(diisopropylamino)borbromid (1) reagiert mit Aluminium-oder Galliumtribromid zu den stabilen Salzen [(iPr2N)2B]EBr4 (2, 3), während 1 mit Silber-triflat Bis(diisopropylamino)-[(trifluormethyl)sulfonyloxy]boran (4) liefert. Silber-tetratriflatoborat setzt sich mit 1 zu einem Gemisch von 4 mit dem Salz [(iPr2N)2B]B(OSO2CF3)4 (6) um. Ferner entsteht (Diisopropylamino)bis[(trifluormethyl)sulfonyloxy]boran (7).

Notes: Die Synthese und physikalischen Eigenschaften der neuen Titelverbindungen vom Typ 9 aus Carbonsäure-Derivaten 3 und CH-aciden Verbindungen 4 werden beschrieben.

Notes: Neue Dianion-sulfide 1a-c entstehen bei der Reaktion der Kaliumsalze von Thiodeltaten 4a,b mit den Deltainen 5a,b. Die Darstellung neuer Thiocarbonyl-ylide 7a-d bzw. 8a-d mit Cyclopropenium- und Deltatfunktionen gelingt durch Umsetzung der Thione 6a-d mit den Deltainen 5a,b oder aus dem Cyclopropenium-Salz 9 mit dem Kalium-thiodeltat 4a. Interessanterweise entsteht das Thiocarbonyl-ylid 7d auch durch Umsetzung des schwefelverbrückten Dianions 1d mit dem Dikation 10. Die spektrometrischen Daten der neuen Verbindungen 1,7 und 8 werden diskutiert und die 13C-NMR-Daten der Thiocarbonyl-ylide mit denen der Dianion- und Dikation-sulfide verglichen.

Notes: (2-Azoniaallenyliden)pentacarbonylwolfram-tetrabromoaluminat-Komplexe [(CO)5W(CNCR2)]+AlBr4- (2-AlBr4) (CR2=C(C6H4Br-4)2 (a), CPh2 (b), C(C6H4OMe-4)2 (c), C(C6H4)2O (d), C(2,4,6-C6H2Me3)2 (e))  -  darstellbar durch Umsetzung von (CO)5W[C(OEt)N=CR2] (1) mit Albr3  -  reagieren mit frisch destillierten Tetrahydrofuran zu neutralen trans-Bromo(2-azaallyliden)-Komplexen trans-Br(CO)4W(CNCR2) (3) und wenig (CO)5W—C≡N—[CR2]2—N≡C—W(CO)5 (4). Die Verbindungen 4. entsprechen dem Produkt einer reduktiven Dimerisierung zweier Kationen 2. 4b wird zum Hauptprodukt der Umsetzung, wenn 1b (oder der entsprechende Methoxy-Komplex 5) mit BBr3 anstatt AlBr3/THF umgesetzt wird. Wie die spektroskopischen Daten von 3 sowie die Ergebnisse der an 3b durchgeführten Röntgenstrukturanalyse zeigen, führt der Austausch eines CO-Liganden in den Kationen 2 gegen Br- unter Bildung von 3 zu einer drastischen Veränderung der Bindungsverhältnisse im CNCR2-Liganden. 3a-e sind die ersten Verbindungen, in denen ein stark gewinkeltes CNCR2-Fragment als Komplexligand fungiert. Durch BBr3-induzierte Fragmentierung von (CO)5W[C(NPh2)N=C(Ph)OMe] (6) wurde der Aminocarbin-Komplex trans-Br(CO)4W≡CNPh2 (7) dargestellt.

Notes: Hexafluoraceton (HFA) reagiert mit N,N-Dialkylcyanformamidinen in einem Reaktionsschritt unter milden Bedingungen zu 4-(Dialkylamino)-2,5-dihydro-5-imino-2,2-bis(trifluormethyl)oxazolen 1a-d. 1a,b könne mit weiterem HFA zu den N′-(hydroxyhexafluorisopropyl)substituierten Derivaten 2a,b umgesetzt werden. Unter der katalytischen Wirkung von Kupferpulver in DMF gelingt die Umlagerung von 1a,b in 1,2-Dihydro-2,2-bis(trifluormethyl)-5H-imidazol-5-one 3a,b in guten Ausbeuten. Von 1a,c und 3a wurden durch 1H-DNMR-Untersuchungen die Aktivierungsparameter der gehinderten Rotation um die C-4—N-Bindung bestimmt.

Notes: 6,7-Dihydrooxepine, -thiepine und -azepine (1-5) zeigen eine ausgeprägte Alternanz ihrer 13C-NMR-Verschiebungen im konjugierten π-System. Das 6,7-Dihydroazepin 3 reagiert mit Acetylendicarbonsäureestern zunächst unter Cycloaddition-Ringerweiterung an der 4,5-Doppelbindung zu den intermediären 8,9-Dihydro-1H-azoninen 6b. Diese ergeben sogleich unter thermischem 6π-Elektronenringschluß die Indole 7a,b. Nach erneuter Umlagerung entstehen 2,3,3a,7a-Tetrahydroindole 8a,b; die Konstitution von 8a wird durch Röntgenstrukturanalyse ermittelt. Mit 4-R-1,2,4-Triazolin-3,5-dionen (4-R-TAD) entstehen aus 3 und 5 in polarer [2 + 2]-Cycloaddition die [1,2,4]Triazolo[1′,2′:1,2]diazet[3,4-d]azepine 10a-d und 11a,b mit dem Bis-TAD 12 das 2:1-Addukt 13. 10a ergibt mit Phenylisocyanat das Carbodiimid 14 und beim basischen Ringschluß das Pyrimido[4,5-b]azepin 15.

Notes: (α-Lithioalkyl)diphenylarsanoxide (2) sind wegen ihrer bequemen Zugänglichkeit und hohen Nucleophilie günstige Reagenzien zur Darstellung zahlreicher Organoarsenverbindungen. In der organischen Synthese sind sie als Reagenzien für indirekte nucleophile Haloalkylierungen (Hal=Cl, Br, I) empfehlenswert.

Notes: Im Gegensatz zu α-lithiierten Alkyldiphenylphosphanoxiden reagieren die α-lithiierten Alkyldiphenylarsanoxide 3a und b hoch diastereoselektiv mit Benzaldehyd zu den Alkoholen erythro 4a bzw. erythro-4b. Auch mit Acetophenon reagiert 3b extrem diastereoselektiv, während bei der Umsetzung mit aliphatischen Aldehyden ein Diastereomeren-Gemisch anfällt (erythro:threo = 1.5-1.7:1).

Notes: Durch Einführung eines ortho-Substituenten in die Phenylreste von (α-Lithiobutyl)diphenylphosphanoxid (7) wird die Diastereoselektivität bei der Umsetzung mit Benzaldehyd gesteigert. (α-Lithiobutyl)bis(2-methoxyphenyl)phosphanoxid (9) reagierte mit Benzaldehyd sogar ausschließlich zum erythro-Produkt 12.  -  Der Austausch des Lithiumatoms von (Lithiomethyl)diphenylphosphanoxid (17) gegen Chrom oder Titan führte zu stark erhöhter Aldehydselektivität bei Konkurrenzversuchen mit dem Substratpaar Benzaldehyd/Acetophenon.

Notes: A diastereospecific chain elongation of the aldehydes 1 of anti-α-alkyl-β-hydroxy esters 2 via the intermediates 4-7 is described. By means of the Sharpless epoxidation, 2 may be obtained with 〉90% ee in either enantiomer.

Notes: Aus den kinetisch stabilisierten Cyclobutadienen 6a bzw. b und den Isonitrilen 7a-c erhält man die Azapentafulvene 9a-d. Im Gegensatz dazu reagiert 6a mit 7d ausschließlich unter Bildung des konstitutionsisomeren Azapentafulvens 11e. Beide Möglichkeiten (9f und 11f) werden bei der Umsetzung von 6a mit 7e wahrgenommen. Die Strukturzuordnung der Isomeren 9 und 11 beruht auf 13C-NMR-Untersuchungen sowie auf der Röntgenstrukturanalyse für 9a. Hydrolyse von 9 und 11 macht die tri-tert-butylsubstituierten Cyclopentadienone 20a,b und 21 zugänglich. Photochemisch läßt sich 21 in das Isomere 20a umwandeln, das auch unmittelbar aus dem Cyclobutadien 6a und Kohlenmonoxid erhalten werden kann.

Notes: Die deprotonierten Acetamide 4a-c und 5a-c werden an prochirale Carbonylverbindungen addiert. Dabei wird der Einfluß von Lösungsmittel, Temperatur und Enolat-Gegenion auf das jeweilige Verhältnis der isomeren Produkte 8/9, 18/19 und 26/27 untersucht. Die höchsten Diastereoselektivitäten lassen sich mit dem Titan-enolat des Amids 4a und dem dreifach deprotonierten N-Acetyl-α-phenylglycinol (5a) erzielen. Die bei der Addition von 5a an Aldehyde im Überschuß gebildeten Diastereomeren 18a-d können durch einmaliges Umkristallisieren rein erhalten werden und liefern nach alkalischer Hydrolyse die enantiomerenreinen β-Hydroxycarbonsäuren 3a-d. Dabei wird der chirale Hilfsstoff, α-Phenylglycinol (14), zurückgewonnen.

Notes: Die Azibenzile 1a-e reagieren mit Nonafluorbutansulfonsäureanhydrid (Nf2O) hauptsächlich zu den Vinylen-bis(nonafluorbutansulfonaten) E,Z-2a-e und den Benzilen 3a-e. Um die Zersetzung der Azibenzile durch Säurespuren im Anhydrid zu vermeiden, ist der Zusatz eines nicht nucleophilen Amins erforderlich. Die Produkte 2 gehen aus einer einleitenden O-Sulfonylierung der Azibenzile hervor, für die Bildung der Benzile könnte eine C-Sulfonylierung verantwortlich sein. Diazodiphenylmethan wird durch Nf2O zu Tetraphenylethylen, Benzophenon und Benzophenon-azin zersetzt.

Notes: Wir berichten über 15 neue disubstituierte Bullvalene (2, 4, 5, 11, 12, 14-20, 22-24) und diskutieren ihr Substitutionsmuster gemeinsam mit dem von 9 bekannten Vertretern (1, 3, 6-10, 13, 21). Die teilweise unerwarteten Ergebnisse werden phänomenologisch geordnet. Für einige Befunde fehlen befriedigende Erklärungen. So bevorzugen z. B. nur manche Substituenten mit „komplementären“ Eigenschaften wie das Paar CH2OH/Br oder CH3/CN in den Verbindungen 16 bzw. 18 eine vicinale Anordnung an der Doppelbindung.

Notes: Als potentielle Carbonyl-ylide vereinigen sich die 1,3-Oxathiolylium-4-olate 1c oder 1d mit Dibenzoylacetylen oder 1-(Diethylamino)-1-propin über nicht isolierbare [3 + 2]-Primäraddukte vom Typ 2 unter COS-Abspaltung zu Furan-Derivaten 3a bzw. b. Demgegenüber reagieren einige Vertreter von 1 mit symmetrisch und unsymmetrisch substituierten olefinischen Substraten regio- und/oder stereoselektiv zu isolierbaren [3 + 2]-Primäraddukten 4-16. Am Beispiel der Umsetzung von 1c mit trans- und cis-Cycloocten werden die Stereospezifitäten und die Konkurrenzkonstante ermittelt. Weiterhin werden die Thermolysen der Cycloaddukte 4b, 5, 6 und 7a,b untersucht. Die aus der FMO- und PMO-Theorie abgeleiteten Additionsrichtungen werden mit der experimentell realisierten Regiochemie verglichen.

Notes: Die Hydrierung von Homocuban (6a) mit Pd-, Pt- und Rh-Katalysatoren führt zu zwei Dihydroverbindungen 5a und 7a, von denen nur das unsymmetrische Hauptprodukt rasch zu Twistbrendan (8a) weiterreagiert. Durch Umlagerung von Homocuban zu Homocunean (9a) und dessen Hydrierung entstehen daneben auch bis zu 20% Brendan (11a). Im Falle des 9-Keton-Ethylenacetals 6b kann über Rh/Al2O3 der Anteil am symmetrischen Dihydroprodukt 5b bis 40% betragen, im Falle des Carbonsäureesters 6d erhält man dagegen nur 7d und 8d, aber kein 5d.

Notes: The products and the kinetics of the thermolysis of the title compounds 3 and 5 were investigated. Like the trans-isomers, the cis-azo compounds also undergo homolytic decomposition without accompanying cis-trans-isomerization. The observed structure-reactivity relationships are discussed. On irradiation of trans-tetra-tetr-butylazomethane (trans-5) at 60-120°C in benzene or chlorobenzene an almost quantitative yield of 1,1,2,2-tetra-tert-butylethane is obtained.

Notes: Die 1H-Isoindole 1e-k werden durch Ligandenaustausch mit Pentacarbonyl(η2-cis-cycloocten)chrom (3) in die Pentacarbonylchrom-Komplexe 4e-k übergeführt; tautomeriefähige 2H-Isoindol (2a-d) werden ebenfalls in der 1H-Form komplexiert (4a-d). Diese Reaktion erlaubt erstmals, auch das unsubstituierte 1H-Isoindol (1a) aus dem Gleichgewicht mit 2H-Isoindol (2a) in Form eines stabilen Derivats 4a zu isolieren. Die Struktur 4 der Pentacarbonyl(η1-1H-isoindol)chrom-Komplexe ergibt sich aus den analytischen und spektroskopischen Daten (IR, 1H- und 13C-NMR, MS) und wird durch eine Röntgenstrukturanalyse des 3-Ethoxy-1H-isoindol-Komplexes 4e bestätigt.

Notes: Die in ω-Position unsubstituierten 2,3-Butadienanilide 6a-h werden auf dem Inaminweg synthetisiert und der Thermolyse unterworfen. Sie isomerisieren ohne Ausnahme in einer intramolekularen Diels-Alder-Reaktion mehr oder weniger rasch, irreversibel und quantitativ zu den tricyclischen Lactamen 8a-h, wobei der Anilinkern jeweils als „Dien“ fungiert. Die Strukturen 8 werden spektroskopisch und durch eine Röntgenstrukturanalyse (8b) bestätigt.

Notes: Aus Trialkylboroxinen (RBO)3 (1) [1a: R=CH3; 1b: R=C2H5] bilden sich bei ≈ 20°C mit enolisierbaren 1,3-Diketonen (R′CO)2CH2 [2a: R′=CH3; 2b: R′=C6H5] unter raschem Abbau der Boroxin-Ringe in bis zu 85proz. Ausbeute die monochelatisierten Diboroxane 3 der Zusammensetzung HOB(R)OB(R)OC(R′)CHC(R′)O [3aa: R=R′=CH3; 3ba: R=C2H5, R′=CH3; 3bb: R=C2H5, R′=C6H5]. Die festen 3 mit H-verbrückter bicyclischer Struktur stehen in Lösung im Gleichgewicht mit partiell ringgeöffneten Verbindungen (1H-, 11B-, 13C- und 17O-NMR-Daten). Aus 1b erhält man mit 2a und aus Triphenylboroxin (1c) mit 2b die zweifach chelatisierten Diboroxane [RB(R′CO)2CH]2O [4ba: R=C2H5, R′=CH3; 4cb: R=R′=C6H5]. 1c reagiert mit 2a oder 2b bei 〉 140°C unter langsamer Protolyse der B-Phenylreste zu den einfach und zweifach chelatisierten Boroxinen 5 und 6 mit den Zusammensetzungen R2B3O3(R′CO)2CH [5ca: R=C6H5, R′=CH3; 5cb: R=R′=C6H5] und RB3O3[(R′CO)2CH]2 [6cb: R=R′=C6H5]. 4, 5 und 6 mit vollständig bzw. partiell chelatisierten Bor-Atomen sind bis 〉 200°C stabil.  -  Die Molekülstrukturen von 4cb und 5ca wurden durch Röntgenstrahlbeugungsanalysen bestimmt.

Notes: Michael-Addition von Methylenmalonester an das Tetrahydro-10-nitro-5,9-methano-7H-benzocyclohepten-7-on-ethylenacetal 9 lieferte die Ausgangsverbindung 11. Abspaltung der Nitrogruppe, Reduktion der Estergruppen, Entfernung der Acetalgruppe und Umwandlung der Alkoholfunktionen in Tosylate ergab die Verbindung 14. Eine Cyclisierung dieses Produktes führte zum Tetracyclus 17. Bromaddition und Umsetzung mit NaOH ergab 21, das erste bekannte Benzenoadamantanon-Derivat. Die Stereochemie der Zwischenprodukte wurde durch NMR-Untersuchungen ermittelt.

Notes: Durch Reaktion von Metallocen-dichloriden der IV. Nebengruppe M(η5-C5H4R)2Cl2 (R=H: M=Ti, 1a; Zr, 1b; Hf, 1c. R=CH3: M=Ti, 1d mit äquimolaren Mengen der S,N-bzw. N,N′-Dilithium-Salze des o-Aminothiophenols oder o-Phenylendiamins können die Chelat-Komplexe M(η5-C5H4R)2(SC6H4NH) (R=H: M=Ti, 2a; Zr, 2b; Hf, 2c. R=CH3: M=Ti, 2d) und M(η5-C5H5)2(NHC6H4NH) (M=Ti, 3a; Zr, 3b; Hf, 3c) dargestellt werden. Die Struktur der Komplexe 2a-d mit fünfgliedrigen MSC2N-Chelatringen wird anhand ihrer temperaturvariablen 1H-NMR-Spektren diskutiert. Die Fragmentierung der Chelate 2a-d und 3a-c im Massenspektrum wird untersucht.

Notes: Arene(phosphane)metal Complexes, XII. Unexpected Formation of Monohydrido(phosphane)osmium(II) Complexes C6H6OsH[PMe2(OR)]I from C6H6Os(PMe2H)I2. A Compound with an Os=PMe2 Bond as Intermediate?The reaction of [C6H6OsI2]2 (4) with PMe2H produces the compound C6H6Os(PMe2H)I2 (5) which reacts with KO-t-C4H9 in methanol or diethylamine to give the monohydrido-(phosphane)osmium(II) complexes C6H6OsH[PMe2(OR)]I (6a, R=CH3; 6b, R=t-C4H9). The mechanism possibly involves the formation of an intermediate 7 containing an Os=PMe2 bond.

Notes: 5,6-Dihydro-2H-pyrans by [4+2]-Cycloaddition of Diethyl Mesoxalate to 1-Alkoxy-1,3-butadienesThe enantiomers of diethyl 3-alkyl-2-ethoxy-5,6-dihydro-2H-pyran-6,6-dicarboxylates 3 are obtained under mild conditions in yields 〉95% by [4+2]-cycloaddition of diethyl mesoxalate 2 to 2-alkyl-1-ethoxy-1,3-butadienes 1 which are easily prepared by Wittig alkenylation of 2-alkyl-3-ethoxyacroleins.

Notes: The 4,5-dihydro-2-(methylthio)-1H-imidazoles 1a,b react with active methylene compounds 2a-f to afford the corresponding substituted methyleneimidazolidines 3a-f and 4c-f by elimination of methanethiol. The reaction of compounds 2g-j, which contain a more active carbonyl group, with 1a gives 3g-i by elimination of a methylthio group as well as an acyl group, too. 3a,g-i react with esters of α,β-unsaturated acids to afford the corresponding imidazo[1,2-a]pyridines 5,6, and 7 in an addition and cyclocondensation reaction sequence, but with diethyl azodicarboxylate only to give the addition product 8.

Notes: Eine Reihe von Trifluoralkanaminen (9, 26, 35, 38, 45, 56 und 67) wurde dargestellt und diazotiert (Wasser, pH 3.5), um den Einfluß von Trifluormethylgruppen auf die Reaktionsweise aliphatischer Diazonium-Ionen zu untersuchen. Die Produktverteilungen zeigen, daß α-CF3-Gruppen die invertierende Substitution verstärken und Umlagerungen (Wasserstoffverschiebungen) fördern, welche die positive Ladung von der CF3-Gruppe trennen. Die Wanderung der positiven Ladung von der β- zur γ-Position wird weniger stark gefördert als die von α nach β. Aus dem Vergleich mit analogen Alkandiazonium-Ionen lassen sich Beschleunigungsfaktoren von ca. 15 (α → β) und 4 (β → γ) ableiten. In umgekehrter Richtung (β → α) wandert die positive Ladung nicht, abgesehen von einem kleinen Anteil Pinakol-Umlagerung (68 → 7). Eine Ladungsverschiebung von der γ- zur β-Position wurde bei 36 gefunden; im Vergleich zum analogen Butandiazonium-Ion 37 ist sie um den Faktor 10 verringert. Alle Beobachtungen sind im Einklang mit der relativen Stabilität der intermediären Trifluoralkyl-Kationen.

Notes: EHT- und MINDO/3-Rechnungen an endo- und exocyclischen Vierringcarbenen mit 4π (1), 6π (2 und 6) und 8π (8) Elektronen werden vorgestellt. Blitzthermolysen und Photolysen der entsprechenden Carbenvorläufer führen zu den intramolekularen Reaktionsprodukten 18. Intermolekulare Reaktionen liefern 15, 19, 20. Entsprechende Multiplizitäten von 1, 2, 6 und 8 werden erörtert.

Notes: Die im Titel genannten sechsgliedrigen Ringsysteme mit -Gerüst lagern bei höherer Temperatur in fünfgliedrige Ringe mit -Gerüst unter Erhaltung der B—B-Bindung um. In Konkurrenz zu dieser Isomerisierung tritt eine Redoxdisproportionierung, die mit länger werdender C—C-Bindung (vgl. die Reihe 6 〈 8 〈 15) der Isomerisierung den Rang abläuft. Nur eine der beiden Dimethylamino-Gruppen von 2-[Bis-(dimethylamino)boryl]-1,3,2-dithiaborol (7a) kann elektrophil gegen ein Halogenatom substituiert werden.

Notes: Ausgehend von 6-Brom-2-methoxy-1,3-azulendicarbonsäure-diethylester (1) werden Methoden zur Einführung unterschiedlicher Reste in 2- und 6-Position entwickelt. 2-Substitution gelingt durch Grignard-Reaktion oder Austausch der Alkoxygruppe sowie durch Aldol-Kondensation von 2-Methylverbindungen, während 6-Substitution durch nucleophilen Austausch und durch Homo- und Kreuz-Aromaten-Kupplungen erfolgt. Anschließende Dealkoxycarbonylierung erbringt Azulene 20 mit freien 1,3-Stellungen. Die Biazulene 9a-c und 201, 20m, die Styryl- und Bis(styryl)azulene 15-18 und 20i-k sowie der Azulendialdehyd 19 sind Verbindungen, die bisher schwierig oder nicht zugänglich waren.

Notes: Die Synthese und physikalischen Eigenschaften sowie einige mit dem MNDO-Verfahren berechnete Daten der Titelverbindungen vom Typ 5a-e und 8, die zur Klasse der mesoionischen 6π-Hetarene zählen, werden beschrieben.

Notes: Durch Templat-Kondensation von Arylisocyaniden (1) (Ar=C6H5, p-MeC6H4, p-NO2C6H4, p-CH3OC6H4, o-CH3OC6H4) mit Carbenkomplexen (CO)5M=C(OC2H5)R (2) (M=Cr, Mo; R=C6H5, 2-Thienyl, CH3) erhält man die 3-Amino-2-aroyl(bzw. acyl)indole 10, 2-Alkylidenindolenine 16, Pyrazino-diindole 18 oder Azetidine 13. Die Cyclisierung zu Indolen wird durch elektronenreiche, die Bildung von Azetidinen durch elektronenarme Arylisocyanide begünstigt. Entsprechend liefern erstere mit 2 in Gegenwart von Wasser gute Ausbeuten an 10, letztere in Gegenwart von Ethanol hingegen bevorzugt einen offenkettigen Imidsäureester 11 und ein Azetidin 13. In aprotischem Medium fällt 13 als Hauptprodukt an. 13 liegt als Isomerengemisch vor, das unter Rotation um die exo-C=C-Bindung rasch äquilibriert (ΔG≠ = 57.4 kj/mol) und leicht zum Säureamid 20 hydrolysiert. Das C4-Gerüst von 20 baut sich letztlicht aus drei Isocyanid- und einem Carbenkohlenstoff auf. Elektronenreiche Arylisocyanide bilden mit 2 die Pyrazino-diindole 18 durch Dimerisierung eines intermediären 2-Alkylidenindolenins 16. Das 2-Alkylidenindolenin 16e konnte monomer gewonnen werden, da seine Dimerisierung durch den Raumbedarf der 7-OCH3-Gruppe verhindert wird. Alle hier beschriebenen Reaktionen verlaufen über Keteniminkomplexe 3, die Isocyanide am zentralen C-Atom der NCC-Einheit addieren.

Notes: The photohydration of phenylacetylene yields acetophenone enol as a transient primary product which was detected by flash photolysis. The identification of the transient intermediate rests on a quantitative comparison of its decay kinetics with that of authentic acetophenone enol generated by Norrish type-II photoelimination from γ-hydroxybutyrophenone in aqueous HCl and aqueous AcOH buffer solutions.

Notes: With the aim to investigate the influence of structural isomerism on the mesomorphic thermal stability in main chain thermotropic polycondensates, a series of poly(azomethines) and low molecular weight models have been prepared. The model compounds exhibit smectic and/or nematic mesophases whose stabilites are very sensitive to structural modifications. On the basis of the above results, monomers 2, 5, 6, 8, 9, 23, 25, and 26 were selected to synthesize oligomers 27-23. The oligomer 33 obtained from the nonsymmetric diamine 23 has a lower melting point than the symmetric oligomer 28, but a similar liquid crystalline range.

Notes: The syntheses, photolyses, and thermolyses of the α,β-unsaturated silyl ketones (E/Z)-7, (E)-8, and (E)-9 are described. On n,π*-excitation (λ 〉 347 mm), the aforementioned compounds undergo (E/Z)-isomerization followed by γ-H abstraction. The intermediate enols are trapped intermolecularly by siloxycarbenes leading to the dimeric acetals 27A + B, 30A + B, and 31A + B. In addition, the acylsilanes (E/Z)-7 undergo photoisomerization by δ-H abstraction furnishing the acylsilanes 29A + B. Flash vacuum thermolyses (FVT) of (E/Z)-7, (E/Z)-8, and (E)-9 give rise to intramolecular reactions of the siloxycarbene intermediates. Thus, FVT (520°) of (E)- and (Z)-7 selectively leads to the enol silyl ethers 32 and (E)-33, respectively, arising from carbene insertion into an allylic C--H bond. FVT of (E/Z)-8 (560°) and (E)-9 (600°) affords the trienol silyl ethers 34A + B and the cyclic silyl ethers 37A + B, respectively, which are formed by CH insertion of the siloxycarbenes. As further products of (E)-8 and (E)-9, the bicyclic enol ethers 35 and 36 are formed, presumably via siloxycarbene addition to the cyclohexene C=C bond.

Notes: Synthesis of (Methylthio)penam Derivatives via Keten Addition onto 4,5-Dihydro-5-(methylthio)-1,3-thiazolesThe 4,5-dihydro-5-(methylthio)-2-phenyl-1,3-thiazoles 3a and 3b, easily prepared from the corresponding 1,3-thiazol-5(4H)-thiones and MeLi, react with dichloroacetyl chloride (5a) and acidoacetyl chloride (5b) in the presence of Et3N to give (methylthio)penam derivatives 6 (Table 1). The reaction mechanism is either a [2 + 2] cycloaddition of in situ generated ketene or a two-step reaction (Scheme 2). The structure of 6f has been confirmed by X-ray crystallography (Fig. 2). The relative configuration of 6a-e follow from comparison of their 1H-NMR spectra with those of 6f (Fig. 1). The 6-azidopenams 6d and 6f have been reduced to aminopenams 8a and 8b, respectively. Acylation of 8a with phenacetyl chloride yields 9 (Scheme 4).

Notes: Since we found certain structural features of triaziridine (1) obtained by MNDO calculations to be in qualitative agreement with those derived earlier from ab initio calculations, we used the MNDO method to derive properties of formyltriaziridine (2) and 1-formyl-2,3-diisopropyltriaziridine (3) as models for the preparatively known 2,3-dialkyl-triaziridine-1-carboxylates 4 and 5. The main results are: (a) The triaziridine N-atoms with H, alkyl, or formyl as substituents (see 2 and 3) are pyramidal. N(1) carrying the formyl group is flatter than N(2) and N(3) with H or alkyl substitent. Bond lengths and angles at N(2) and N(3) are almost identical with those calculated for the N-atoms of 1. (b) The MNDO inversion barriers at the H-substituted N(2) and N(3) of 2 are higher than those at the formyl-substituted N(1), but similar to the ab initio barriers at the N-atoms of 1. (c) The MNDO inversion barriers at N(1) of 2 and 3 are 53 to 92 kJ/mol, whereas the rotation barriers around the N(1)-C(4) bond are 7 to 23 kJ/mol; thus, the previously observed dynamic NMR phenomena in trans-2,3-diisopropyltriaziridine-carboxylates (5) can now be assigned to the slowing down of N(1) inversion rather than N(1)-C(4) rotation.

Notes: Synthesis and Structure Elucidation of Merucathinone and Synthesis of Cathinone. Constituents of Catha edulis FORSK.Starting from L-alanine, two constituents of Catha edulis FORSK., (S)-4-amino-1-phenylpent-1-en-3-on ((S)-3; merucathinone) and (S)-2-amino-1-phenylpropan-1-on ((S)-1; cathinone) were synthesized.

Notes: The relative configuration of the title compounds has been determined by 1H-NMR measurements at 300 MHz. In contradistinction to prevailing opinion, it was found that 4-oxo derivatives prefer the cis-configuration. While the cis/trans ratio is 82:18 for the parent 1,2,3,4,4a,9,10,10a-octahydrophenanthrene-4,9-dione, the trans-isomers of C(5)-substituted derivatives cannot be detected under the conditions of equilibration. The cis-configuration is retained upon acetalization of the 4-oxo derivative. A warning is issued regarding the assigned configurations of certain intermediates in the Elad-Ginsburg synthesis of morphine.

Notes: The Mediterranean stolonifer Sarcodictyon roseum ( = Rolandia rosea) (Cnidaria, Anthozoa, Alcyonaria, Stolonifera, Clavulariidae) contains the first example of a chiral, optically active prenyl derivative of a reduced benzoquinone, sarcodictyenone (= (+)-(4R*,5R*)-5-geranylgeranyl-4-hydroxy-2-methylcyclohex-2-en-1-one; (+)-1a).

Notes: Nucleophilic Addition of Lithiumorganyles to N,N-Diethyl-10-(trimethylsilyl)-1,6-methano[10]annulene-2-carboxamideReaction of lithiumorganyles with N,N-diethyl-10-(trimethylsilyl)-1,6-methano[10]annulene-2-carboxamide followed by quenching with H2O or MeI yields 2,3-dihydro derivatives of 1,6-methano[10]annulene.

Notes: Synthesis of 3-Nitro-1,1-bis(triisopropylsilyl)-1H-cyclopropabenzene and Derivatives of Azocyclopropabenzene1,1-Bis(triisopropylsilyl)-1H-cyclopropabenzene (4) can be nitrated at C(3) without opening of the three-membered ring. Further functionalized cyclopropabenzenes are available in this way.

Notes: Ab initio calculations of structure, properties, and tautomerization reactions of triazene (1) at the HF/3-21G//3-21G, HF/6-31G*//6-31G*, HF/6-31G**//6-31G*, and MP2/6-31G*//6-31G* levels led to the following conclusions and predictions: (a) Calculations of the ground-state structure of (E)- and (Z)-triazene (1a and 1b, respectively) at various levels of theory show for both isomers C1 geometry with a rather flat pyramidal configuration at N(3), and small energy differences (0.2-7.2 kJ/mol) between C1 and Cs geometry, i.e. inversion at N(3) is a quasi-free process. With all levels of calculations, 1a is found to be of lower energy than 1b by 23-30 kJ/mol. (b) Comparison of vibrational frequencies of (E)-diazene (3) calculated at the HF/3-21G level with experimental values reveals that HF/3-21G calculations are reliable for the prediction of vibrational frequencies of polyaza compounds, if corrected by a factor of 0.91. On this basis, the harmonic vibrational frequencies of 1a and 1b were predicted. (c) For the rotation around the N(2) - N(3) bond of 1a two conceivable transition states, 5a (syn) and 5b (anti) were located (HF/3-21G). The energy differences between 5a or 5b, and 1a are in the order of magnitude of 50-56kJ/mol and show a slight preference for the anti-mode, i.e. energy barriers for the N(2) - N(3) rotation are obtained comparable to those observed experimentally with substituted (E)-triazenes (4). (d) Protonation of 1a at N(1), N(2), or N(3) leads to 6a, 6b, and 6c, respectively -the last one resembling an intermediate of formation of 1 from hydrogendiazonium ion (7) and ammonia (8). Energetically, the conjugate acids of 1a follow the sequence 6a 〈 6c 〈 6b. (e) The preference of N(1) protonation of 1a is also reflected in the relatively high gain of energy in the formation of H-bonded dimers of 1a with H-bonds from N(3) - H to N(1). Calculations of three different H-bonded dimers 9a-c of 1a with the 3-21G basis show that an eight-membered cyclic dimer 9c with two H-bonds from N(3)—H to N(1) is energetically most favoured (67.5 kJ/mol below two separate molecules of 1a). This dimer might well be the starting situation of double intermolecular H-transfer leading to an automeric dimer 9c via an energetically low-lying transition state 12, thus offering a low-energy pathway for the known easy tautomerization of mono- or disubstituted (E)-triazenes. For 9c⇄9c, the activation energy including correction for polarization and correlation effects as well as for vibration zero-point energy is estimated to be ca. 54kJ/mol. (f) A six-membered cyclic dimer 9b of 1a with two H-bonds from N(3)—H to N(2) might be involved for double H-transfer via a transition state 11 to a dimer 10 of (E, Z)-azimine (2). This process, however, turns out to be energetically highly disfavoured (estimated energy barrier for 9b→10: 232 kJ/mol) in contrast to the reverse reaction (10→9b via 11: 4 kJ/mol). This leads to the prediction that azimines bearing an H-atom at N(2) might be kinetically too instable for isolation, being, instead, easily tautomerized to triazenes by bimolecular H-transfer.

Notes: Carbophilic Additions of Organocuprates and 1,3-Thiazole-5(4H)-thionesOrganocuprates and 1,3-thiazole-5(4H)-thiones 1 react in THF at 0° via carbophilic addition onto the C—S bond to give 4,5-dihydro-1,3-thiazole-5-thiols 3 (Scheme 3). This observation is in marked contrast to the previously described reaction of organolithium compounds and 1, which undergo a thiophilic addition onto the exocyclic S-atom. As an exception, treatment of the 1,3-thiazole-5(4H)-thione 1a with tert-butyl cuprate leads to 7a (Scheme 3).

Notes: Cyclometallated complexes of the type cis-bis(2-phenylpyridine)platinum(II) (C22H16N2Pt) and cis-bis(2-(2′-thienyl)pyridine)platinum(II) (C18H12N2S2Pt) undergo thermal or photochemical oxidative addition (TOA or POA) reactions with a number of substrates. TOA (with CH3I, CH3CH2I etc.) yield mixtures of several isomers which rearrange slowly (within ca. one week at room temperature) to one of the possible cis-isomers. CH2Cl2, CHCl3, or (E)—ClCH=CHCl, e.g., do not react thermally. POA yield directly complexes of Pt(IV) with the halide and a σ-bonded C-atom in cis-position. The configuration, as assigned by extensive use of 1H-NMR data, can be characterized for the two chelating ligands C … N and C′ … N′ by C,C′-cis; N,N′-cis and C(chelate), Cl-trans.

Notes: On the Photochemistry of (Z,Z)-2,7-Cyclodecadien-1-one and 4,8-Cyclododecadien-1-one. Synthesis and Properties of Tricyclo[5.3.0.02,8]decane SystemsIrradiation of (Z,Z)-2,7-cyclodecadien-1-one (3) yields (Z,Z)-3,7-cyclodecadien-1-one (12) or tricyclo-[5.3.0.02,8]decan-4-one (16), depending on the reaction conditions. Irradiation of 4,8-cyclododecadien-1-one (28) results also in a light-induced transannular [2 + 2] cycloaddition, yielding tetracyclo[7.3.0.02,1003,6]dodecan-1-one (30). Starting from 16, the preparation of tricyclo[5.3.0.02,8]dec-4-ene (19), tricyclo[5.3.0.02,8]dec-4-ene (21) and tricyclo[5.3.0.02,8]deca-3,5-diene (24) is described. The 1H-NMR and 13C—NMR spectra of the newly prepared compounds are discussed. In the case of 19, 21, and 24, the electronic structure is discussed on hand of their PE spectra.

Notes: Metabolites of 1,5-Dihydroimidazo[2,1-b ]quinazolin-2(3H)-ones. Preparation and Reactions of Some 1,5-Dihydro-3-hydroxyimidazo[2,1-b]quinazolin-2(3H)-onesHydroxylated 1,5-dihydroimidazo[2,1-b]quinazolin-2(3H)-ones 2-4 and 6 were isolated as metabolites of imidazoquinazolinones 1a and 1b, respectively. The synthesis of 1,5-dihydro-3-hydroxy-3-methylimidazo[2,1-b]quinazolin-2(3H)-ones 3, 4, and 6, and the preparation of some derivatives thereof is described.

Notes: Succesive treatment of chiral esters 1 with LiN(i-Pr)2/Me3SiCl and di(tert-butyl) azodicarboxylate/TiCl4/Ti(i-PrO)4 gave N,N′ -di[(tert-butoxy)carbonyl]hydrazino esters 9 which on deacylation, hydrogenolysis, transesterification, and acidic hydrolysis furnished (2S)-α-amino acids 6 in high enantiomeric purity with efficient recovery of the auxiliary alcohol 7.

Notes: The hydroxylation of geraniol (8) by cytochrome P-450 (P-450Cath.) from the subtropical plant Catharanthus roseus (L.) G. DON was optimised to give 8-hydroxygeraniol (9) as the single product in 35% yield. Incubations of different 13C- and 2H-labelled geraniols revealed that H-abstraction is completely regioselective in favour of the CH3 group trans to the chain at C(6) of 8. An intramolecular isotope effect kH/kD = 8.0 was determined, suggesting that H-abstraction is one of the major rate-contributing steps; however, the intermolecular isotope effect was surprisingly inverse at low conversion kH/kD = 0.50, indicating the existence of rate-contributing steps preceding the first irreversible, isotope-sensitive reaction in the sequence.

Notes: Nitrocyclohexene undergoes facile SnCl4-induced, [4 + 2]-cycloadditions with simple cycloalkenes to produce nitronates. The nitronates can be transformed sterospecifically into a number of other functional groups (alcohol, ketone, oxime, amine) by hydrolytic, reductive, and oxidative processes. The mechanism of the [4 + 2]-cycloaddition is believed to involve formation of a zwitterionic intermediate which can collapse via competing pathways to form the observed products. 1,3-Dipolar cycloadditions of the nitronates are described.

Notes: Combined NOE and Decoupling Experiments for the Selective H-NMR Detection: Application to a Stereochemical ProblemThe successful solution of complex stereochemical problems by NMR methods often requires scalar (J) and dipolar (NOE) data. A modern method, improved with respect to sensitivity and selectivity, which yields both scalar and dipolar informations is proposed, and an application to configurational analysis is demonstrated. The method is based on NOE effects for the detection of selected protons and homonuclear decoupling for improved resolution.

Notes: The two tetraazamacrocycle-N,N′,N″,N‴-tetraacetic acids H4dota and H4teta form with Ni2+, Cu2+, and Zn2+ (M2+) mononuclear complexes MLH2 and M′[ML], M′ being an alkaline earth ion. The structures of Ni(H2dota) and Cu(H2dota) have been solved by X-ray structure analysis. The metal ions are in a distorted octahedral geometry coordinated by four amino N-atoms and two carboxylates. In the case of Cu2+, the distortions are more pronounced than for Ni2+ indicating that the Jahn-Teller effect is operating. Starting from these two structures, the coordination geometry of the other complexes is discussed using VIS and IR spectra.

Notes: The solvolysis rates and products of 4- and 5-exo-substituted 2-exo- and 2-endo-norbornyl tosylates 9 and 10, respectively, are reported. The logarithms of the rate constants (log k) correlate linearly with the inductive constants σIq for the substituents. A comparison of the reaction constants p1 for the 4-, 5-, 6-, and 7-substituted 2-exo- and 2-endo-tosylates 9, 10, 1, and 2 respectively, indicates that inductivity is higher for 2-exo-ionization than for 2-endo-ionization in all series. This observation is attributed to the more favorable alignment of neighbouring C-atoms for dorsal participation in exo-ionization, especially, in the case of C(6).

Notes: The He(Iα) PE spectra of the two pairs of 1(Ph)-3 and 2-4 have been recorded and assigned by comparison with spectra of related molecules, or by using simple MO arguments. This analysis shows that the PE spectra are in agreement with the assumption that the twist angles observed in the crystalline state are more or less conserved in the gas phase. The observed first adiabatic ionization energies IIa allow the calculation of the molar reaction enthalpy ΔrHmθ which accompanies the enolization of the radical cations of the title compounds. It is found that ΔrHmθ ≍ --70 kJ mol-1 is roughly the same for both keto/enol pairs, in qualitative and quantitative agreement with expectation. These results complement and correct ionization energies determined previously by mass spectrometric methods and conclusions based on them.

Notes: N-Acetylneuraminic acid (1) can be transformed into the methyl α-D-ketoside 2 which, by reaction with methanesulfonyl chloride, yields the corresponding 4-O-mesylate 3 and the 4,7-di-O-mesylate 4 as a by-product. Compound 3 reacts with Nal giving the 4-deoxy-4-iodo compound 5 with equatorial orientation of the I-atom. As second product, the dihydrooxazole 6 is produced. Catalytic hydrogenation of 5 is followed by ester cleavage and removal of the isopropylidene group yielding the methyl α-D-ketoside 8 which affords the title compound, N-acetyl-4-deoxyneuraminic acid (9), by reaction with fowl plague virus sialidase. Further biochemical activities of 8 and 9 are reported.

Notes: A synthesis of 1,2-cis-configurated, non-isosteric phosphonate analogues of aldose-1-phosphates is described. Treatment of 1-O-acyl-glycoses 1, 7, 13, and 19 with trialkyl phosphite in the presence of trimethylsilyl trifluoromethanesulfonate gave the 1,2-cis-configurated glycosylphosphonates 2, 4, 8, 10, 14, 16, 20, and 22 as the major anomers and the 1,2-trans-configurated glycosylphosphonates 3, 5, 9, 11, 15, 17, 21, and 23 as the minor anomers. The 1,2-cis-configurated phosphonates 4, 10, 16, and 22 were deprotected to give the (β-D-glucopyranosyl)phosphonate 6, the (β-D-mannopyranosyl)phosphonate 12, the (β-D-ribofuranosyl)phosphonate 18, and the (β-D-arabinofuranosyl)phosphonate 24, respectively, in high yields. The preferred formation of 1,2-cis-configurated phosphonates is explained by postulating an equilibrium between the anomeric phosphonium-salt intermediates (such as 25 and 26) and a stabilization of the cis-configurated salts through formation of a pentacoordinated species (such as 28).

Notes: C45-and C50-Carotenoids: Synthesis of (S)-TrisanhydrobacterioruberinThe Synthesis of (S)-trisanhydrobacterioruberin ((S)-1) is reported.

Notes: Optically pure (-)-trans-μ-[(1R,2R,3S,4S,5S,6R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6,7-pentamethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((-)-9), (-)-trans-μ-[(1R,2R,3S,4S,5S,6R,7S)-C,2,3,C-η:C,5,6,C-η-(7-methyl-2,3,5,6-tetramethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((-)-10), and (-)-trans-μ-[(1R,2R,3S,4S,5S,6R,7R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6-tetramethylidene(7D)bicyclo[2.2.2]octane)]bis(tricarbonyliron) ((-)-16) have been prepared. Their CD spectra were solvent- and concentration-independent, but temperature-dependent, in accord with the existence of equilibria between rapidly interconverting diastereoisomeric species which can be interpreted as arising from distortions of the tricarbonyl(diene)iron units from the Cs symmetry.

Notes: The fast-atom-bombardment mass spectra (FAB-MS) of a series of ribo- and deoxyribonucleosides and -nucleotides were examined in both positive-ion and negative-ion modes. Behaviour of cytosine analogs having unnatural bases (2(1H)-pyrimidone, 2(1H)-pyridinone, and 4-amino-2(1H)-pyridinone) was similar to that of compounds having naturally occurring bases. Nucleotides protected by dimethoxytrityl and p-chlorophenyl groups were also investigated using this technique. Use of negative-ion mode reduces interference from positive counter-ions (e.g., Na+) and allows rapid sequence determination of simple di- and trinucleotides.

Notes: The tetra(tert-butyl)[14]annuleno[14]annulene 1 is transformed, via alkali metal reduction, into its radical monoanion, dianion, radical trianion, and tetraanion. The paramagnetic species are characterized by ESR and ENDOR spectroscopy and the diamagnetic species by 1H- and 13C-NMR spectroscopy. Well-resolved ESR and NMR spectra can only be obtained, if the reduction is carefully monitored. For the interpretation of the data, the ions derived from the structurally related [14]- and [22]annulenes 3 and 5 as well from the tetra(tert-butyl)[14]annuleno[18]annulene 2 serve as suitable model compounds. While the behavior of the neutral annulenoannulene 1 is governed by that of the [14]annulene-subunit, the corresponding ionic systems can best be described as macrocyclic perimeters. This outcome can be rationalized by the nodal properties of the frontier MO's.

Notes: The electronic structure of [4.2.2]propella-2,4,7,9-tetraene (1), 2,5-etheno[4.2.2]propella-3,7,9-triene (2), and of several hydrogenated derivatives of 2 has been investigated using He(I) PE spectroscopy and MO calculations. It is found that in 2 the 1,4-cyclohexadiene moiety interacts considerably with the bicyclo[2.2.0]hexadiene unit, while in 1 the interaction between the butadiene fragment and the Dewar benzene unit is minute. The syntheses of 3-5 are reported.

Notes: CO and H2 are photogenerated simultaneously by visible-light irradiation of systems containing a photosensitizer, the [Ru(bpy)3]2+ complex, Co(II) species as homogeneous catalysts, which mediate CO2 and H2O reduction by intermediate formation of Co(I), a tertiary amine as electron donor, which provides the electrons for the reduction, and an organic solvent which also facilitates dissolution of CO2. The efficiency of (CO + H2) gas production and the selectivity CO/H2 markedly depend upon the composition of the medium, the nature of the tertiary amine, the solvent, and the ligand of the Co ions. 2,9-Dimethyl-1,10-phenanthroline is particularly effective in promoting CO and H2 formation, giving a quantum yield of 7.7% in (CO + H2) (1.2% for CO and 6.5% for H2). The process consists of two catalytic cycles: a photocatalytic cycle for the Ru complex and a double dark reaction pathway for the Co species; oxidative and/or reductive quenching of the excited state of the photosensitizer lead to the formation of Co(I) species which reduce either CO2 or H2O to CO or H2, respectively.

Notes: The complexation properties of the open-chain N2S2 ligands 1-4 are described and compared to those of analogous N2S2 macrocycles 5-7. With Cu2+, the open-chain ligands give complexes with the stoichiometry CuL2+ and CuLOH+, the stabilities and absorption spectra of which have been determined. The ligand field exerted by these ligands is relatively constant and independent of the length of the chain. With Cu+, the species CuLH23+, CuLH2+, and CuL+ were identified and their stabilities measured. The redox potentials calculated from the equilibrium constants and measured by cyclic voltammetry agree and lie between 250 and 280 mV against SHE. The comparison between open-chain and cyclic ligands shows that (1) a macrocyclic effect is found for Cu2+ but not for Cu+, (2) the ligand-field strength is very different for the two types of ligands, and (3) the redox potentials span a larger interval for the macrocyclic than for the open-chain complexes.

Notes: The syntheses of 2,3,5-trimethylidenebicyclo[2.2.1]heptane (1) and 2,3,5,6,7-pentamethylidenebicyclo[2.2.2]-octane (2) are reported. The Diels-Alder additions of the diene moieties of these polyenes can be regioselective, probably because of a possible transannular interaction between the homoconjugated methylidene and s-cis-buta-diene groups.

Notes: Regioselective Functionalisation of N,N-Diethyl-1,6-methano[10]annulene-2-carboxamidesLithiation of N,N-diethyl-1,6-methano[10]annulene-2-carboxamide with BuLi followed by quenching with different electrophiles yields 2,10-disubstituted-1,6-methano[10]annulenes.

Notes: A highly regio- and stereoselective Diels-Alder reaction between dienophiles of type I and dienes of type II (Scheme 1) gives rise to Diels-Alder adducts of type III. Upon treatment with BF3.Et2O, these adducts are smoothly converted into the corresponding enones (Scheme 6). Under mild acidic conditions, enone (±)-33 gave bicyclic diketone (±)-34 via an intramolecular Michael-type addition. Diketone (±)-34 has the correct relative configuration and a suitable ketone function at C(6) for further conversion into the hexahydrobenzofuran portion of the avermectins and milbemycins.

Notes: EtAlCl2-promoted additions of organocopper reagents to camphor-derived, conjugated N-enoyl-sultams gave saturated and olefinic β-silylcarboxyl derivatives with high diastereodifferentiation. Nondestructive removal of the chiral auxiliary followed by oxidative Si-C bond cleavage furnished enantiomerically pure acetate-derived aldols and propionate-derived ‘anti’ -aldols (via silyl-directed α-methylation).

Notes: Synthesis of 6,7-Dihydro-2H-pyrimido[6,1-a]isoquinolin-4(3H)-ones and Analogous Compounds and their Activity as Blood-Platelet InhibitorsThe synthesis of 6,7-dihydro-2H-pyrimido[6,1-a]isoquinolin-4(3H)-ones and of analogous compounds is described. These compounds are powerful phosphodiesterase inhibitors and, therefore, inhibit blood-platelet aggregation independent of the agonist. They exhibit, too, cardiac activities. However, there is evidence for selective action. A structure-activity relationship for platelet-aggregation inhibitors is discussed.

Notes: Enantiomerically Pure Pyrrolidine Derivatives from trans-4-Hydroxy-L-proline by Electrochemical Oxidative Decarboxylation and Titanium-Tetrachloride-Mediated Reaction with NucleophilesPreparative electrolysis of N-methoxycarbonyl-O-[(t-butyl)dimethylsilyl]hydroxyproline 4 in MeOH leads to substitution of the COOH by a MeO group (oxidative decarboxylation). The mixture 5 of the two diastereoisomers (ca 1:1) thus obtained was reacted in CH2Cl2 with nucleophilic silylated compounds (such as allylsilane, silyl cyanide and 1-phenyl-1-silyloxyethane) or with trimethyl phosphite in the presence of TiCl4 to give 2-allyl-, 2-cyano-, 2-(2-oxo-2-phenylethyl)- and 2-phosphono-substituted hydroxypyrrolidines, respectively, with high diastereoselectivities (≥ 90%, products 6-12). The configuration of two of the products (6/7 and 8/9) was shown to be cis.

Notes: Cyclophane-Metal Complexes: Synthesis and Crystal Structure of ([3.3]Paracyclophane)gallium(I) Tetrabromogallate(III)[3.3]Paracyclophane forms 1:1 complexes 2a and 2b with both Ga[GaCl4] and Ga[GaBr4]. The crystalline products obtained from toluene solution at room temperature are much less sensitive to air and moisture than most other arene complexes of Ga(I). Solubilities in standard organic solvents are very low, suggesting coordination polymers. The X-ray diffraction analysis of 2b confirms the presence of a two-dimensional network. Both aromatic rings of each cyclophane molecule are η6-coordinated from the outer side to Ga(I)-atoms. The position of these metal cations is 2.75 Å above the ring centres. The arene rings are parallel within each cyclophane, but tilted by 48.5° with respect to those of the neighbouring cyclophane. The coordination sphere of the Ga(I) centres is completed by two Br-atoms of two GaBr4- anions, which link the Ga(I) cations to give … Ga[GaBr4] Ga[GaBr4]Ga … strands. The double interconnection of the Ga(I)-atoms gives rise to a two-dimensional sheet structure, which is thus different from the structure of the previously described Ga[GaBr4] complex of [2.2]paracyclophane, where a three-dimensional network was observed.

Notes: The low-temperature addition of tertiary phosphites to [(allyl)Fe (CO)4]+X- complexes proceeds regio- and stereospecifically and produces metal-coordinated β-olefinic trialkoxyphosphonium ions. These can be converted by various routes into the uncomplexed phosphonium salts or phosphonates. Similar reactions of acyclic [(dienyl)Fe(CO)3]+X- compounds give metal-coordinated (2,4-dien-1-yl)trialkoxyphosphonium salts or dialkyl (2,4-dien-1-yl)phosphonates. The mechanisms and their relationship to the classical Michaelis-Arbuzov reaction are discussed. The new compounds are characterized, if possible, by 1H-, 13C-, and 31P-NMR spectra. The new phosphonium salts and phosphonates, potentially useful for Wittig-Horner reactions, are difficult to obtain by conventional routes.

Notes: The 1,4-endoperoxide, prepared from 3-(4-methylnaphth-1-yl)propanal by photo-oxygenation in CH2Cl2, gave on treatment with Amberlyst-15®, 3,10b-epidioxy-2,3,4a,10b-tetrahydro-6-methyl-1H-naphtho[2,1-b] pyran in 85% yield. Its structure was determined by X-ray crystal structure analysis. The 1,2,4-trioxane moiety is locked in a twist-boat conformation with trans fusion to the parent six-membered ring. The 1,4-endoperoxides of the methyl, butyl, and phenyl ketone analogues of the aforementioned aldehyde underwent similar acid-catalyzed rearrangement to the corresponding bridged bicyclic trioxanes in 94, 47, and 48% yields, respectively.

Notes: Preferred conformation, orientation, and accumulation of substance P on a neutral hydrophilic-hydrophobic interface was estimated and extrapolated to interactions with neutral and anionic lipid bilayer membranes according to our general procedure. Nine residues at the C-terminus were predicted to be transferred to the hydrophobic phase as an α-helical domain, oriented quite perpendicularly on the membrane surface. The N-terminal residues remained in the aqueous phase with their charges exposed to H2O. The molecular amphiphilic moment vector was strong (338 arbitrary units) and pointed its hydrophilic end towards the N-terminus, only 15° away from the helix axis. The molecular electric dipole moment vector was also strong (124 debye) and pointed its positive end towards the N-terminus, only 9° away from the helix axis. Thus, it reinforced the effect of the amphiphilic moment of a peptide intruding into the membrane dipole layer. The estimated dissociation constant for the equilibrium between membrane-bound and free substance P was Kd ≍ 46 mM for neutral membranes, and Kd ≍0.43 mM for anionic membranes with a Gouy-Chapman surface potential of -40 mV. Thus, substance P behaved similarly to dynorphin A and adrenocorticotropin peptides which insert their N-terminal message segments as perpendicularly oriented helical domains into membranes, whereas their C-terminal address segments remain in the aqueous phase as random coils. Substance P is the first instance of a neuropeptide which is expected to insert a C-terminal message into lipid membranes.

Notes: Enantiomerically pure β-necrodol (1) and its 1-epimer 16 have been synthesized starting from aldehyde 5. The two key steps are an asymmetric conjugate addtion/Mannich reaction tandem (10→12) and a type-II-magnesiumene cyclization/oxidation sequence (14→1 + 16).

Notes: Lipophilic neutral carriers were synthesized which show Li+/Na+ selectivities of up to ca. 80 in highly lipophilic liquid membranes. The sensor membranes exhibit improved response times and increased lifetimes as compared to systems described earlier. They allow reliable measurements of Li+ in blood serum within the clinical concentration range. A 1:1 Li+/ionophore complex of one representative (N,N,N′,N′-tetracyclohexyl-5,5-dimethyl-3,7-dioxaazelaamide) has been prepared, and its structure was elucidated by X-ray analysis.

Notes: The polymer-bound heptapeptide H-Glu-His-Pro-Gly-Ser-Gly-PEGM was designed as a ‘single-centre model’ for the active site of α-chymotrypsin. The peptide was synthesized according to the general principles of the liquid-phase method for peptide synthesis, and its conformational properties were investigated by CD and IR spectroscopy in solution and in the solid state. In harmony with empirical prediction codes, experimental and theoretical conformational considerations, the peptide adopts a β-turn conformation stabilized by H-bonds involving the side chains of Glu, His, and Ser. The development of a H-bonded system similar to the active site of α-chymotrypsin leads to implications with respect to a possible catalytic activity of the model peptide.

Notes: The Stereochemistry of the Nucleophilie Opening of the Cyclopropane Ring in the four Diastereoisomeric Lanugons J (Spirocoleons)Methanolysis of the spiro(methylcyclopropane) moiety in the four diastereoisomeric lanugons J 3 (13S, 15R), 4 (13R,15R), 5 (13S,15S), and 6 (13R,15S) is shown to proceed stereospecifically with inversion of the configuration at the attacked C-atom (C(15)). The resulting epimeric 2-methoxypropyl-substituted hydroxy-1,4-benzoquinones (royleanones) 7a/8a (monomethoxy derivatives) and 7b/8b (dimethoxy derivatives) could be separated by HPLC using the recently described ‘Non-Aqueous Cation Exchange System’. Respective pairs of 1H-NMR spectra exhibit minute but significant differences in the ABMX3 part of the 2-methoxypropyl group. The final structure assignment is based on a single-crystal X-ray analysis of the dimethoxyroyleanone 7b, whose absolute configuration was established by chiroptical correlation with known abietanoids. Thus, methanolysis of 3 and 4 ((R)-configuration at the reaction centre) yielded the royleanones 7a and 7b with (S)-configuration, whereas analogous treatment of 5 and 6 ((S)-configuration at the reaction centre) led to the corresponding derivatives 8a and 8b both having the (R)-configuration in the 2-methoxypropyl side chain.

Notes: Hydrogenation of the ketone group in di-O-benzylderivative (8) of the known macrocyclic lactone zeralenone (7) using a novel chiral borane complex 3. BH3, prepared in situ, proceeded at lower temperatures with moderate diastereoselectivity (∼40%, d. e. at -60°). Unsaturated diastereomers 9 and 10 were separated, and 9 converted into zeranol (11), a known anabolic agent. Restricted conformational mobility at lower temperatures is assumed for the intermediate 8 on the basis of the temperature-dependent CD spectra of its acetyl congeners 18 and 19. X-Ray structure analysis of 7-O-acetylderivative (13) of 11 revealed the (R)-configuration at C(7). Two crystallographically independent H2O molecules are involved in the H-bonds, one of them (O(21)) rises the helices of the molecules of 13 along b. Small positive torsional angle [C(16)-]C(161)-C(1) [=O] (+19.3°), transoid(E) conformation of the lactone group, and nearly achiral arrangement of the C(11)-C(12) bond (torsional angle [C(11)-]C(12)-C(121)[C(161)] is -93°) are the main conformational features that differentiate the macrocylic RAL (resorcinic-acid lactone) derivatives from the 6-membered lactone derivative 20, studied earlier by CD. Consequently, the rules developed for the CD effects within conjugation band (around 270 nm), and n→π* band (around 255 nm) of the latter compound, cannot be applied the macrocyclic lactones.

Notes: Results of voltammetric, potentiometric, chronoamperometric, ion transport, and extraction studies on neutral carrier based, plasticized poly(vinyl chloride) membranes are summarized. They unambiguously confirm that such bulk membranes dispose of immobile anionic sites. These fixed sites lead to a Donnan exclusion of other anions from the membrane and thus to a permselectivity for cations. The results are in perfect agreement with the predictions of earlier membrane models. A rigorous Poisson-Boltzmann analysis of macroscopic liquid membranes clearly indicates that space-charge at the membrane/solution interfaces does not influence the electrochemical properties and the ion-selectivity behavior at steady state.

Notes: (R)-3-Hydroxybutyric acid (from the biopolymer PHB) and pivalaldehyde give the crystalline cis - or (R,R)-2-(tert-butyl)-6-methyl-1,3-dioxan-4-one (1a), the enolate of which is stable at low temperature in THF solution and can be alkylated diastereoselectively (→3, 4, 5, and 7). Phenylselenation and subsequent elimination give an enantiomerically pure enol acetal 10 of aceto-acetic acid. Some reactions of 10 have been carried out, such as Michael addition (→11), alkylation on the CH3 substituent (→13), hydrogenation of the C=C bond (→1a) and photochemical cycloaddition (→16). The overall reactions are substitutions on the one stereogenic center of the starting β-hydroxy acid without racemization and without using a chiral auxiliary.

Notes: A synthesis of N-acetylneuraminic acid (1) and of N-acetyl-4-epineuraminic acid (2, R = H) from 2-acetamido-4,6-O-benzylidene-1,2-dideoxy-1-nitro-D-mannopyranose (3) and 2-acetamido-1,2-dideoxy-4,6-O-isopropylidene-1-nitro-D-mannopyranose (4), respectively, is described. Michael addition of 3 and 4 to tert-butyl 2-(bromomethyl)prop-2-enoate (5) and subsequent hydrolytic removal of the NO2 group gave the 4-nonulosonate tautomers 6/7 and 8/9, respectively (Scheme). Stereoselective reduction of 6/7 and 8/9 with NaBH4/AcOH in dioxane/H2O yielded 12/13 (94:6) and 14/15 (92:8), respectively. Reduction of 6/7 and 8/9 in the absence of AcOH or in EtOH gave 12/13 (15:85) and 14/15 (15:85), respectively. Ozonolysis of 12 and 13 followed by hydrolysis gave tert-butyl neuraminate 22 and tert-butyl 4-epineuraminate 24, respectively. Ozonolysis of 14/15, separation of the products 20 and 21, and hydrolytic removal of the isopropylidene groups gave 22 and 24, respectively. The tert-butyl ester 22 was saponified to give 1, which was further characterized as the methyl ester 23. Saponification of 24 gave the crude 4-epimer of 1, which was converted into the stable Na salt 2 and also into the methyl ester 25.

Notes: Novel Heterocycles: Tetrazinodi(heteroarenes), Synthesis and StructureA series of 7 new symmetric tetrazinodi(heteroarenes) is obtained in a two-step synthesis by N-aminating heterocyclic compounds substituted with a leaving group and by treating the latter with an organic or inorganic base. The new compounds are characterized, and the postulated structures are confirmed by X-ray analysis of a representative example.

Notes: Structure and Reactivity of Xanthocorrinoids. C(15) Hydroxylation of the Corrin Chromophore on Reaction of Cyanocob(III)alamin with Udenfriend's ReagentHydroxy-corrinoid 4 represents a new type of corrin derivatives whose chromophore is identical with that of products formed on bacterial degradation of cyanocob(III)alamin (1). In vitro, 4 is obtained by O2 oxidation of 1 in the presence of ascorbic acid and cupric ions.

Notes: Reaction of 3-(Dimethylamino)-2H-azirines with 1,3-Thiazolidine-2-thioneReaction of 3-(dimethylamino)-2H-azirines 1 and 1,3-thiazolidine-2-thione (6) in MeCN at room temperature leads to a mixture of perhydroimidazo[4,3-b]thiazole-5-thiones 7 and N-[1-(4,5-dihydro-1,3-thiazol-2-yl)alkyl]-N′,N′-dimethylthioureas 8 (Scheme 2), whereas, in i-PrOH at ca. 60°, 8 is the only product (Scheme 4). It has been shown that, in polar solvents or under Me2NH catalysis, the primarily formed 7 isomerizes to 8 (Scheme 4). The hydrolysis of 7 and 8 leads to the same 2-thiohydantoine 9 (Scheme 3 and 5). The structure of 7a, 8c, and 9b has been established by X-ray crystallography (Chapt. 4). Reaction mechanisms for the formation and the hydrolysis of 7 and 8 are suggested.

Notes: Three new bidesmosidic saponins 1-3 have been isolated from the berries of Phytolacca dodecandra L′HERIT (Phytolaccaeae). The structures have been established by spectroscopic (1H-NMR, 13C-NMR, FAB-MS, DCI-MS, and GC/MS) and chemical methods (acid, basic, and enzymatic hydrolysis). Saponins 1 and 3 are tetra- and pentaglycosides of oleanolic acid, whereas 2 is a tetraglycoside of bayogenin. The corresponding prosapogenins 1a-3a, obtained by cleavage of a glucose unit esterified at C(28), exhibited strong molluscicidal activity against schistosomiasis-transmitting snails.

Notes: The two bis-macrocycles 4 and 5 in which the tetraaza units are separated by a chain of different length, have been synthesized using 1,4,7-tritosyl-1,4,7,11-tetraazacyclotetradecane as starting compound and bifunctional alkylating agents. The bis-macrocycles give binuclear complexes with Ni2+ and Cu2+, the properties of which have been studied to obtain information about the interaction of the two subunits as a function of the distance. The VIS spectra of the Ni2+ and Cu2+ complexes indicate that both metal ions are in a square-planar geometry as expected from the results of the analogous complexes with 1,4,7,11-tetraazacyclotetradecane 7. Cyclic voltammetry and differential pulse polarography of the binuclear Ni2+complexes in CH3CN show a single two-electron step for ligand 5, whereas two distinct one-electron redox processes can be observed for ligand 4, indicating that the two metal ions interact with each other when the chain length is shorter. Similarly, the EPR studies of frozen solutions of the binuclear Cu2+ complexes clearly show that a magnetic dipolar interaction between the two paramagnetic centers exists, and that the strength of it depends upon the length of the bridge. Finally, from the X-ray structures of the binuclear Ni2+ complexes with 4 and 5, it is seen that the two rings are kept apart as far as possible, the distances between the two metal ions determined in the solid correlate well with the observations in solution.