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  • Wiley-Blackwell  (120)
  • National Academy of Sciences  (26)
  • 2020-2022  (5)
  • 1995-1999  (73)
  • 1975-1979  (66)
  • 1940-1944  (2)
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  • 1
    Electronic Resource
    Electronic Resource
    Protonenresonanz-Spektroskopie ungesättigter Ringsysteme, XXI. Überbrückte [14]Annulene mit Anthracenperimeter (1975)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 108 (1975), S. 640-656 
    Details
    ISSN: 0009-2940
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Proton Resonance Spectroscopy of Unsaturated Ring Systems, XXI. Bridged[14]Annulenes With Anthracene PerimeterThe 1H n.m.r. spectra of bridged [14]annulenes with anthracene perimeter have been analysed. The H, H coupling constants obtained show all systems to possess a delocalised 14-π electron system. The increased shielding of the perimeter 1H resonances in α- and β-position as well as the simultanous deshielding of the bridge protons observed with increasing number of links in the bridge is attributable to geometric factors. No indications for a significant reduction of cyclic π-electron delocalisation and, as a consequence, of the diamagnetic ring current effect are found. In the case of 1, 6:8, 13-pentanediylidene-[14]annulene a conformational mobility of the bridge was detected for the first time in this series of compounds. For the assumed inversion process ΔH≠ = 13.7 kcal/mole and ΔS≠ = -0.5 e. u. were determined by lineshape analysis at different temperatures. PPP-type calculations with variable resonance integral β allow satisfactory predictions of the perimeter CC bond length, if transannular interactions of β (1, 6) = -1.1 eV for the [10]annulene and β(1,6) = β(8, 13) = -0.3 eV for the [14]annulene are considered.
    Notes: Die 1H-NMR-Spektren überbrückter [14]Annulene mit Anthracenperimeter wurden analysiert. Nach den ermittelten H, H-Kopplungskonstanten besitzen alle Systeme ein delokalisiertes 14-π-Elektronensystem. Die mit zunehmender Brückengliederzahl eintretende Abschirmung der Perimeter-1H-Resonanzen in α- und β-Position und die gleichzeitig zu beobachtende Entschirmung der Brückenprotonen kann auf geometrische Faktoren zurückgeführt werden. Für eine signifikante Beeinträchtigung der cyclischen π-Elektronendelokalisation und damit des diamagnetischen Ringstromeffekts ergeben sich keine Hinweise. Bei 1,6:8,13-Pentandiyliden-[14]annulen wird erstmals für diese Verbindungsklasse eine konformative Beweglichkeit der Brücke festgestellt. Für den angenommenen Inversionsprozeß findet man durch Linienformanalyse bei verschiedenen Temperaturen ΔH≠ = 13.7 kcal/mol und ΔS≠ = -0.5 Clausius. PPP-Rechnungen mit variablem Resonanzintegral β gestatten eine gute Vorhersage der Perimeter-CC-Bindungslängen, wenn für die transannulare Wechselwirkung β (1,6) = -1.1 eV im [10]Annulen und β (1,6) = β (8,13) = -0.3 eV im [14]Annulen angenommen wird.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19751080230
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  • 2
    Electronic Resource
    Electronic Resource
    Reduction of 5,6-Dimethylidene-exo-2,3-epoxynorbornane with Metal Hydrides. Efficient syntheses of 6-methyl-5-methylidene-anti-3- nortricyclanol and of 2,3-dimethylidene-anti-7-norbornanol (1978)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 61 (1978), S. 732-740 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: 5,6-Dimethylidene-exo-2,3-epoxynorbornane (1) is reduced slowly by LiAlH4 in boiling tetrahydrofuran (THF) and furnishes a mixture of 5,6-dimethylidene-exo-2-norbornanol (2), 2,3-dimethylidene-anti-7-norbornanol (3) and principally 6-methyl-5-methylidene-anti-3-nortricyclanol (4). The yield of 4 is the highest for low initial concentrations of LiAlH4; it decreases in favour of alcohols 2 and 3 at high concentration of LiAlH4. The reduction of 1 with AlH3 in THF yields 3 as the major product, thus revealing an efficient synthesis of 7-substituted-2, 3-dimethyl-idenenorbornane derivatives. No alcohol 2could be isolated by LiEt3BH reduction of 1. LiAlD4 reduces 1 into the monodeuterated alcohols 2-d, 3-d and 4-d. The deuterium label is found in the endo-position at C (3) in 2-d, in the exo-position at C(5) in 3-d and in the methyl group of the tricyclic alcohol 4-d. Mechanistic limits for the formation of 2, 3 and 4 are discussed briefly.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19780610221
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  • 3
    Electronic Resource
    Electronic Resource
    Selective Hydrogen Chloride Elimination from Primary Chlorides Induced by the Fluoride Anion. Anchimeric participation of the chloromethyl group in the heterolytic opening of an epoxide. Stereospecific syntheses of 5,6-bis (methylidene)-syn-2-norbornen-7-ol and 5,6-bis (methylidene)-endo-3-chloro-exo-2-norbornanolPart of this work was presented at the autumn meeting of the «Societé Suisse de Chimie» in Bern, Oct. 7, 1977.Dedicated to Professor H. Dahn on his 60th anniversary (1979)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 62 (1979), S. 511-524 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Syntheses of the alcohols 10 and 18, and the corresponding ketones 11 and 19 are presented. Endo-5, exo-6-bis (chloromethyl)-endo-3-chloro-exo-2-norbornanol (16) and endo-5-(bromomethyl)-exo-6-(chloromethyl)-endo-3-chloro-exo-2-norbornanol (17) were obtained by HCl- and, respectively, HBr-addition to endo-5, exo-6-bis (chloromethyl)-exo-2, 3-epoxynorbornane (5). The Wagner-Meerwein rearrangement was precluded in these reactions probably because of the formation of a relatively stable chloronium ion 15 arising from the participation of the 1,4-chlorine atom of the endo-5-chloromethyl group in the heterolytic ring opening of the epoxide 5.The ‘naked’ fluoride anion (excess CsF in DMF or KF in DMF with 18-crown-6-ether) permitted the selective elimination of 2 equivalents of HCl from 16 and yielded the chlorohydrin-diene 18.
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19790620218
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  • 4
    Electronic Resource
    Electronic Resource
    Synthesis of Polypropionate Fragments Containing Tertiary-Alcohol Moieties. Cross-aldolisations with lithium enolates of 7-oxabicyclo[2.2.1]heptan-2-one derivativesFor a preliminary report, see [1]. Part of the Ph.D. thesis of Ph. K., Ecole Polytechnique Fédérale de Lausanne, 1994. (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 301-324 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Diels-Alder adduct of 2,4-dimethylfuran to 1-cyanovinyl (1′R)-camphanate ((+)-(1R,2S,4R)-2-exo-cyano-1,5-dimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl (1′R)-camphanate ((+)-1)) was converted into (+)-2,7-dideoxy-2,4-di-C-methyl-L-glycero- ((+)-6) and -D-glycero-L-altro-heptono-1,4-lactone ((+)-7), into (-)-(3R,4R,5R,6S)-3,4:5,7-bis(isopropylidenedioxy)-4,6-dimethylheptan-2-one ((-)-22), and into (+)-(2R,3R,4R,5S,6S)-3,4:5,6-bis(isopropylidenedioxy)-2,4-dimethylheptanal ((+)-34). Condensation of ((+)-34 with the lithium enolate of (-)-(1R,4R,5S,6R)-6-exo-[(tert-butyl)dimethylsilyloxy]-1,5-endo-dimethyl-7-oxabicyclo[2.2.1] heptan-2-one ((-)-38; derived from (+)-1) gave a 3:2 mixture of aldols (+)-39 and (+)-40 (mismatched pairs of a α-methyl-substituted aldehyde and (E)-enolate) whereas the reaction of (±)-34 with (±)-38 gave a 10:1 mixture of aldols (±)-41 and (±)-39. A single aldol, (-)-44, was obtained to condensing (+)-34 with the lithium enolate of (+)-(1S,4S,5S,6S)-5-exo-(benzyloxy)-1,5-endo-dimethyl-7-oxabicyclo[2.2.1]heptan-2-one ((+)-43; derived from (-)-(1S,2R,4S)-2-exo-cyano-1,5-dimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl (1′S)-camphanate ((-)-3)). All these cross-aldolisations are highly exo-face selective for the bicyclic ketones. The best stereochemical matching is obtained when the lithium enolates and α-methyl-substituted aldehydes can realize a ‘chelated transition state’ that obeys the Cram and Felkin-Anh models (steric effects). Polypropionate fragments containing eleven contiguous stereogenic centres and tertiary-alcohol moieties are thus prepared with high stereoselectivity in a convergent fashion. The chiral auxiliaries ((1R)- and (1S)-camphanic acid) are recovered at the beginning of the syntheses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780205
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  • 5
    Electronic Resource
    Electronic Resource
    Stereoselective Synthesis of 2,4,6-Trimethylcyclohex-4-ene-1,3-diol Derivatives and of polypropionate fragments with four contiguous stereogenic centersFor a preliminary report, see [1]. (1995)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 78 (1995), S. 325-343 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The Diels-Alder adduct (±)-3 of 2,4-dimethylfuran and 1-cyanovinyl acetate was converted stereoselectively into benzyl 6-(4-chlorophenylsulfonyl)-1,3-exo,5-trimethyl-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl (26) and -2-endo-yl ether (36). Addition of LiAlH4 to the latter led to the 3-O-benzyl derivatives 28 and 37 of (1RS,2SR,3SR,6SR)- and (1RS,2SR,3RS,6SR)-5-(4-chlorophenylsulfonyl)-2,4,6-trimethylcyclohex-4-ene-1,3-diol, respectively. Methylenation of 6-exo-(4-chlorophenylthio)-1-methyl-5-methylidene-7-oxabicyclo[2.2.1]heptan-2-one (16), obtained by reaction of (±)-3 with 4-Cl-C6H4SCl and saponification gave, 6-exo-(4-chlorophenylthio)-1-methyl-3,5-dimethylidene-7-oxabicyclo [2.2.1]heptan-2-one (43), the reduction of which with K-Selectride afforded 6-exo-(4-chlorophenylthio)-1,3-endo-dimethyl-5-methylidene-7-oxabicyclo[2.2.1]heptan-2-endo-ol (44). The 3-O-benzyl derivative 48 of (1RS,2RS,3RS,6SR)-5-(4-chlorophenylsulfonyl)- 2,4,6-trimethylcyclohex-4-ene-1,3-diol was derived from 44 via based-induced oxa-ring opening of benzyl 6-endo-(4-chlorophenylsulfonyl)-1,3-endo-5-endo-trimethyl-7-oxabicyclo[2.2.1]hept-2-endo-yl ether (49). Benzylation of 28, followed by reductive desulfonylation and oxidative cleavage of the cyclohexene moiety afforded (2RS,3SR,4RS,5RS)-3,5-bis(benzyloxy)-2,4-dimethyl-6-oxoheptanal (32).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19950780206
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  • 6
    Electronic Resource
    Electronic Resource
    A New Approach to the Synthesis of Long-Chain Polypropionates Based on the Diels-Alder Monoadditions of 2,2′-Ethylidenebis[3,5-dimethylfuran]Part of the Ph.D. thesis of J.A., University of Lausanne, 1995. (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1393-1414 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Acidic condensation of 2,4-dimethylfuran with acetaldehyde provided 2,2′-ethylidenebis[3,5-dimethylfuran] (7) which added 1 equiv. of methyl bromopropynoate to give a major adduct 8. Regio- and stereoselective hydroboration of the latter 7-oxanorbornadiene derivative followed by alcohol protection and methanolysis of its β-bromoacrylate moiety gave (1RS,2RS,4RS,5SR,6SR,1′RS)-methyl 4-[1′-(3″,5″-dimethylfuran-2″-yl)ethyl]-3,3-dimethoxy-6-exo-[(2-methoxy)ethoxy]-1,5-endo-dimethyl-7-oxabicyclo[2.2.1]heptane-2-endo-carboxylate (24) (Schemes 2 and 3). Reduction of 24 with LiAlH4, followed by H2O and MeOH elimination gave the 3-methyl-idene-7-oxanorbornan-2-one derivative 26 which underwent 7-oxa ring opening through a SN2′ type of reaction with Me2CuLi (Scheme 4). Stereoselective hydrogenation and ketone reduction provided (1RS, 2SR,3RS,4RS,5RS,6RS,1′SR)-1- [1″-(3 ″,5″-dimethylfuran-2″-yl)]-c-3-ethyl-c-5-[(2-methoxyethoxy)m e-c-ethyl-c-c-5-(2-methoxyethoxy)methoxy]-t-4,t-6-dimethyl-cyclohexane-r-1,c-2-diol (32), the oxidative cleavage of which with Pb(OAc)4 generated a 6-oxo-aldehyde 33 (Schemes 4 and 5). Chemoselective protection of 33 and chemo- and stereoselective reductions generated (2RS,3RS,4SR,5SR,6SR,7RS)-7-(3′,5″-dimethylfuran-2′-yl)-2-ethyl-6-hydroxy-4-[(2-methoxyethoxy)methoxy]-3,5-dimethyloct-1-yl pivaloate (36) and its 4-hydroxy 6-epimer 40 (12 and 13 steps, resp., from adduct 8; Scheme 5). Oxidation of the furan ring of 36 led to a (2RS,3SR,4RS,5SR,6RS,7RS)-7-ethyl-3,5,8-trihydroxy-2,4,6-trimethyl-octanoic acid derivative 44, a polypropionate fragment with six contiguous stereogenic centres (Scheme 6).
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790513
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  • 7
    Electronic Resource
    Electronic Resource
    The Effects of Homoconjugated Cyclopropane and Oxirane Rings on the Diels-Alder Reactivity of 2,3-bis (methylidene)norbornane‘Interaction between non-conjugated chromophores’, part 9; part 8 [1], part 7 [2], part 6 [3], part 5 [4], part 4 [5], part 3 [6], part 2 [7], part 1 [8].This work has been presented to the fall meeting of the ‘Société suisse de chimie’, Bern, oct. 1978.Dedicated to Professor Dr. Edgardo Giovannini on his 70th anniversary (1979)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 62 (1979), S. 2341-2349 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Preparation of 6exo, 7exo-bis (methylidene)-tricyclo[3.2.1.02,4]octane (6) is described. The reactivity of 6 towards tetracyanoethylene is evaluated and compared with that of exo-2,3-epoxy-5,6-bis (methylidene)norbornane (5), 2,3-bis-(methylidene)norbornane (1) and other related dienes. The cyclopropane group in 6 exerts an unsignificant rate retardation effect on the Diels-Alder reactivity of this diene relative to that of 1, whereas a relatively important rate retardation effect is caused by the exo-oxirane ring in 5. The observed effects are probably due to electronic factors (through-space and through-bond interactions).
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19790620731
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  • 8
    Electronic Resource
    Electronic Resource
    The Diels-Alder Reactivity of 2,2′-Ethylidenebis[3,5-dimethylfuran] and Exploratory Chemistry of the Mono-adducts (1996)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 79 (1996), S. 1415-1427 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In the presence of Me3Al, 1-cyanovinyl acetate added to 2,2′-ethylidenebis[3,5-dimethylfuran] (1) to give a 20:10:1:1 mixture of mono-adducts 4,5,6, and 7 resulting from the same regiocontrol (‘para’ orienting effect of the 5-methyl substituent in 1). The additions of a second equiv. of dienophile to 4-7 were very slow reactions. The major mono-adducts 4 (solid) and 5 (liquid) have 2-exo-carbonitrile groups. The molecular structure of 4(1RS,1′RS,2SR,4SR)-2-exo-cyano-4-[1-(3,5-dimethylfuran-2-yl)ethyl-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl acetate) was determined by X-ray single-crystal radiocrystallography. Mono-adducts 4 and 5 were saponified into the corresponding 7-oxanorbornenones 8 and 9 which were converted with high stereoselectivity into (1RS,1′SR,4RS,5RS,6RS)-4-[1-(3,5-dimethyl furan-2-yl)ethyl]-6-exo-methoxy-1,5-endo-dimethyl-7-oxabicyclo [2.2.1]heptan-2-one dimethyl acetal (12) and its (1′RS-stereoisomer 12a, respectively. Acetal hydrolysis of 12a followed by treatment with (t-Bu)Me2SiOSO2CF3 led to silylation and pinacol rearrangement with the formation of (1RS,1′RS,5RS,6RS)-4-[(tert-butyl)dimethy lsilyloxy]-1-(3,5-dimethylfuran-2-yl)ethyl]-5-methoxy-6-methyl-3-methylidene- 2-oxabicyclo[2.2.1]heptane (16). In the presence of Me3Al, dimethyl acetylenedicarboxylate added to 12 giving a major adduct 19 which was hydroborated and oxidized into (1RS,1′RS,2″RS,3″RS,4SR,4″RS,5 SR,6SR)-dimethyl 5-exo-hydroxy-4,6-endo-dimethyl-1-[1-(3-exo,5,5-trimeth oxy-2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-2-yl)ethyl]-7-oxabicyclo [2.2.1]hept-2-ene-2,3-dicarboxylate (20). Acetylation of alcohol 20 followed by C=C bond cleavage afforded (1′RS,1″SR,2RS,2′″SR,3RS, 3″SR,4RS,4″SR,5RS)-dimethyl {3-acetoxy-2,3,4,5-tetrahydro-2,4-dimethyl-5-[1-(3-exo,5,5-trimethoxy -2-endo,4-dimethyl-7-oxabicyclo[2.2.1]hept-1-yl)-ethyl]furan-2,5-diyl} bis[glyoxylate] (24).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19960790514
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  • 9
    Electronic Resource
    Electronic Resource
    Long-Distance Effect on One-Bond C—C Scalar couplings upon introduction of a double bond in bicyclic systems (1997)
    New York, NY : Wiley-Blackwell
    Helvetica Chimica Acta 80 (1997), S. 59-64 
    Details
    ISSN: 0018-019X
    Keywords: Chemistry ; Organic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Anomalous variations of one-bond C—C scalar coupling constants are observed in going from trinorbornane-to trinorbornene-like structures. Most notably, a 10-Hz increase is observed in the coupling constant involving the C-atoms of the ethano branch facing the C=C bond. An effect of about half the size is characteristic of higher homologues (bicyclo[2.2.2]octenes), but no such effect is observed for monocyclic molecules.
    Additional Material: 2 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/hlca.19970800105
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  • 10
    Electronic Resource
    Electronic Resource
    Reaktionen des Tripod-Co-Templats CH3C(CH2PPh2)3Co(II) mit funktionalisierten HydrazinenMax Herberhold zum 60. Geburtstag gewidmet. (1996)
    Weinheim : Wiley-Blackwell
    Berichte der deutschen chemischen Gesellschaft 129 (1996), S. 1107-1113 
    Details
    ISSN: 0009-2940
    Keywords: Tripod ligands ; Hydrazines, substituted ; Diazenes ; Cobalt(III), fivefold coordination of ; Cobalt(II), fivefold coordination of ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The coordination behaviour of ligands having the same basic constitution RN=NC(=X)R′ (X = O, NR″, S) in their tripod cobalt derivatives has been analyzed. The ligands themselves may be considered as neutral heterodiene compounds and are in this respect vinylogues to diazenes RN=NRy′. Two- electron reduction of these neutral species results in dianionic heterosubstituted heteroolefins RN- -N=C(X-)R′. Due to their redox ambiguity the oxidation state of the metal M in chelate complexes is not a priori evident. Compounds tripod [5: X, R′ = O, Ph; 6; (X, R′) = (py); 7: X, R′ = S, NH2] are best described as containing low-spin Co(III) and dianionic ligands. Co(II) species are obtained with diethyl azodicarboxylate EtOOCN=NCOOEt as the ligand. In the mononuclear compound, with only one nitrogen and one carbonyl oxygen of the ligand acting as donor groups, the neutral ligand is coordinated to give the high-spin cobalt(II) species tripod (8). In the dinuclear compound 9 with both of the nitrogen atoms and carbonyl groups involved in coordination the dianionic ligand bridges two high-spin cobalt(II) centers to give tripod (9) as a derivative with two fused five-membered chelate rings. In addition to the conventional analytical techniques X-ray structure analyses, cyclovoltametric measurements, magnetic susceptibility and ESR data are used to characterize the compounds.
    Additional Material: 3 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cber.19961290921
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