ALBERT

Notizen: Aromatic Sigmatropic Hydrogen-Shifts in 2-Vinyl- and 2-Allyl-phenolsIt is shown by deuterium labeling experiments that 2-vinylphenols, on heating at 142,5°, undergo aromatic [1,5]-H-shifts whereby o-quinone methides are formed as intermediates (Scheme 7). Thus, heating of 2-isopropenylphenol (6) in a D2O/dioxane mixture leads to a rapid deuterium incorporation into the methylidene group of the isopropenyl moiety (Table 1) whereas its methyl group shows only a slow uptake of deuterium. The latter exchange process can be attributed to intermolecular reactions (Scheme 8). The quinone methide intermediates (e.g. 26, Scheme 8) can be regarded as vinyl homologues of alkyl ketones. Therefore, 26 can exchange hydrogen in both methyl groups by an acid- and base-catalysed mechanism. Indeed, when 6 is heated in D2O/pyridine or D2O/CH3COOD/dioxane, an almost statistical incorporation of deuterium into the methylidene and the methyl group of the isopropenyl moiety is observed (Table 3).As a consequence of thermally induced [1,5]-H-shifts, 2-(1′-propenyl)-phenols undergo rapid (E,Z) isomerization with first order kinetics on heating above 140° in decane solution. Activation parameters are given in Table 4. The observed primary +++++ H/D isotope effect of 3.3 in the (E,Z) isomerization of phenol 8 is in +++ment with intramolecular H/D-shifts in the rate determing step (Scheme 9 +++ Table 5). As expected aromatic sigmatropic [1,5]-H-shifts in 2-(1′-propenyl)-+++ are much faster than aromatic homosigmatropic [1,5]-H-shifts in 2-(2′-+++++)phenols (Scheme 1 and Table 6). The structurally comparable phenols +++ (Z)-10 and (E)/(Z)-14 (Scheme 3) show k([1,5])/k(homo-[1,5]) ≈ 2300 at ++++A more detailed discussion in English is given in [1]. .

Notizen: On the Formation of Polycyclic Ketones in the Reaction of 5, 6-Dimethylidene-bicyclo[2.2.1]hept-2-ene with Diiron-enneacarbonyl5,6-Dimethylidene-bicyclo[2.2.1]hept-2-ene (4), in the presence of diiron-ennea-carbonyl in boiling hexane, produces the endo-and exo-tricarbonyl-iron complex of 4 (endo- and exo-5). A mixture of numerous tricarbonyl-iron complexes with ligands derived from coupling and carbonylation reactions of 4 are also formed. The endo- and exo-5 compounds as well as two tricarbonyl-iron complexes (7 and 8) of penta-cyclic ketones could be isolated and characterized. After oxidative removal of the tricarbonyl-iron groups in the reaction mixture the three pentacyclic ketones 9, 10 and 11 were separated. Structure and configuration of these ketones were deduced from spectroscopic analyses, especially from their 1H- and 13C-NMR. spectra (see tables 1-4). Whereas the symmetric pentacyclic ketone 11 is of a known type (cf. [1]) the two spiroketone 9 and 10 represent compounds of a new type. Their structure and configuration shows that in ironcarbonyl induced thermal cyclopentanone formations, an exocyclic double bond can also take part.

Notizen: On the Stereochemistry of the Aromatic Claisen Rearrangement. Thermal Rearrangement of erythroid and threoid ortho-Dienones.Erythro- and threo-1-methyl-1-(1′-methyl-2′-propynyl)-2-oxo-1,2-dihydronaph-thalene (erythro- and threo-6) as well as erythro- and threo-2,6-dimethyl-6-(1′-methyl-2′-propynyl)-cyclohexa-2,4-dien-1-one (erythro- and threo-8) were obtained together with the corresponding aromatic ethers 5 and 7 by alkylation of 1-methyl-2-naphthol and 2,6-dimethyl-phenol, respectively in alcoholic potassium hydroxide solution with 1-methyl-2-propynyl p-toluenesulfonate (Scheme 2). The diastereoisomeric dienones 6 and 8 were easily separated by column chromatography on silica gel and its relative configuration at C(1) or C(6) and C(1′) deduced from the chemical shifts in their 1H-NMR.-spectra (Table 1). Hydrogenation of 6 and 8 using Lindlar catalyst yielded the corresponding erythro- and threo-configurated (1′-methyl-2′-propenyl)-dienones 10 and 13, respectively (Scheme 3) the thermal rearrangement of which were studied. The following results were obtained: threo-10 rearranged in benzene at 85-105° preferentially via a chair-like (C) transition state to yield 99,5% (E)- and 0,5% (Z)-(2′-butenyl) 1-methyl-2-naphthyl ether ((E)- and (Z)-14; ΔΔG105,7°≠ (C/B) = -4,0 kcal/mol). On the other hand, erythro-10 when heated at 105-125° in benzene gave 84,7% (E)- and 15,3% (Z)-14, i.e. in this case a boat-like (B) transition state is favoured (G105,7°≠ (C/B) = + 1,3 kcal/mol) (Scheme 5 and Table 2). The thermal rearrangement of dienones 13 led to the corresponding ethers 12 as well as p-allyl-phenols 11. Thus, heating of threo-13 at 20-42° in cyclohexane resulted in the formation of 2,5% of ether 12, consisting of 98% of the (E)- and 2% of the (Z)-isomer, and 97,5% of (E)-11 which contained, at a maximum, 0,5% of the (Z)-isomer, (Scheme 6 and Table 3). This means that both rearrangements occurred with a strong preference of the C transition state (G41,6°≠ (C/B, phenol) = -3,3 kcal/mol). On the contrary, erythro-13 when heated at 42-68° in cyclohexane yielded a 3:2 mixture of ether 12 and phenol 11 (Scheme 6). The ethereal part consisted of 88,0% of the (E)- and 12,0% of the (Z)-isomer which again shows that the B geometry predominated in the erythro transition state leading to the ether (G42,7°≠ (C/B)= + 1,3 kcal/mol). In the phenolic part 36-40% of the (E)-isomer and 64-60% of (Z)-isomer were found which means that in the para-Claisen rearrangement of erythro-13 the C arrangement is only slightly favoured (ΔΔG42,7°≠ (C/B)= -0,36 kcal/mol).

Notizen: Tetracarbonyliron Complexes of trans-Cycloalkenes and trans-CycloalkadienesRelatively stable olefin tetracarbonyliron complexes were obtained by reaction of Fe2(CO)9 with trans-cyclooctene (t-1), trans-cyclononene (t-2) and trans-cyclodecene (t-3) (Scheme 2) in pentane solution at room temperature. Furthermore, trans,cis-cycloocta-1,5- and -1,3-diene (t,c-7 and t,c-8) as well as trans,trans,cis-2,8,12-trans-bicyclo[8.4.0]tetradecatriene (t,t,c-9) gave stable complexes only with the trans-configurated double bond (Scheme 3).An olefin tetracarbonyliron complex was also obtained with bicyclo[4.3.1]deca-7,9-diene (10) which reacted only at the strained bridge-head double bond. The IR. spectra of the new complexes are in agreement with an equatorial position of the olefinic ligands in the trigonal bipyramide of the iron.

Notizen: Thermal (E), (Z)-Isomerizations of Substituted PropenylbenzenesThe thermal isomerizations of (E)- and (Z)-3,5-dimethyl-2-(1′-propenyl)phenol ((E)- and (Z)-3), (E)- and (Z)-N-methyl-2-(1′-propenyl)anilin ((E)- and (Z)-4), (E)- and (Z)-3,5-dimethyl-2-(1′-propenyl)anilin ((E)- and (Z)-5, (E)- and (Z)-2-(1′-propenyl)mesitylene ((E)- and (Z-6), (E)- and (Z)-2-(1′-propenyl)mesitylene ((E)- and (Z)-7), (E)- and (Z)-2-(1′-propenyl)toluene ((E)- and (Z)-8), (E)- and (Z)-4-(1′-propenyl)toulene ((E)- and (Z)-9) as well as of (E)- and (Z)-2-(2′-butenyl)-mesitylene ((E)- and (Z)-10) in decane solution were studied (Scheme 2). Whereas the isomerization of the 2-propenylphenols (E)- and (Z)-3 occurs already between 130 and 150° (cf. Table 1), the isomerization of the 2-propenylanilins 4 and 5 takes place only at temperatures between 220 and 250° (cf. Tables 2 and 3). The activation values and the experiments using N-deuterated 4 (cf. Scheme 4) show that 2-propenylphenols and -anilins isomerize via sigmatropic [1,5]-hydrogen-shifts. For the isomerization of the methyl-substituted propenylbenzenes temperatures 〉 360° are required (cf. Tables 4 and 5). The activation values of the isomerization of (E)- and (Z)-6 and (E)- and (Z)-9 are in accord with those of other (E), (Z)-isomerizations which occur via vibrationally excited singlet biradicals (cf. Table 7). Nevertheless, thermal isomerization of 2′-d-(Z)-8 (cf. Scheme 6) demonstrates that during the reaction deuterium is partially transfered into the ortho-methyl group, i.e. 1,5-hydrogen-shifts must have participated in isomerization of (E)- and (Z)-8 (cf. Scheme 8). Under the equilibrium conditions 2,4,6-trimethylindan (17) is formed slowly at 368° from (E)- and (Z)-6, very probably via a radical 1,4-hydrogen-shift (cf. Scheme 9). In a similar way 2-ethyl-4,6-dimethylindan (19; cf. Table 6) arises from (E)- and (Z)-7. Thermolysis of (E)- and (Z)-10 in decane solution at 367° results in almost no (E),(Z)-isomerization. At prolonged heating 19 and 2,5,7-trimethyl-1,2,3,4-tetrahydronaphthalene (20) are formed; these two products arise very likely from an intermolecular radical process (cf. Scheme 10).

Notizen: Dimethylborazid entsteht aus Dimethylborbromid und Tri-n-butylsilylazid als explosive Flüssigkeit, Sdp. 54°C/720 Torr. Aus den 1H- und 11B - NMR-Signalen der Substanz geht hervor, daß sie einem temperaturabhängigen Assoziationsgleichgewicht unterliegt. Die im Bereich 33-4000 cm-1 gemessenen IR-Banden lassen sich einem Strukturmodell der Punktgruppe Cs zuordnen. Einige Aminate von Dimethylborazid werden beschrieben. Beim Zerfall von Dimethylborazid-Pyridin bei 210-220°C entstehen mehr als 30 Verbindungen, darunter in 21proz. Ausbeute als Hauptprodukt Hexamethylborazol.

Notizen: Photochemical Synthesis of 4-Phenyl-3-oxazolin-5-ones and their Thermal Dimerization.Irradiation of 3-phenyl-2H-azirines affords reactive benzonitrilemethylide intermediates, which can be trapped by carbon dioxide to yield 4-phenyl-3-oxazolin-5-ones (Scheme 1). The first section of the paper deals with the experimental description of this reaction, which already has been preliminarily communicated. Upon irradiation the 3-oxazolin-5-ones undergo photoextrusion of carbon dioxide to reform the corresponding benzonitrile-methylides, which can be trapped by dimethyl acetylenedicarboxylate.In the second section of the paper, reactions of 2-methyl-4-phenyl-3-oxazolin-5-one (3c) are described. Upon heating to 130°, this compound is partially converted to 2-methyl-4-phenyl-2-oxazolin-5-one (azlactone 4e). Prolonged heating of 3c affords the dimer 7 (Scheme 3) as well as the imidazole derivative 9 (Scheme 4). Compound 7 is related to the ‘Rügheimer compound’ C18H14N2O4, formed from hippuric acid methylester. The structure of 7 was determined by X-ray crystallography and this supports the formula assigned earlier to the ‘Rügheimer compound’ (12) and related pyrrolidin-2,4-diones. The possible mechanism of the thermal formation of 7, which is also base catalysed, is represented in Scheme 3, the one for the formation of the imidazol 9 in Scheme 4.Under the influence of oxygen the 2,4-diphenyl-3-oxazolin-5-one (3b) undergoes a dehydrodimerization to yield compound 16 (Scheme 7). Section three contains the structure elucidation of compound 16 and a mechanistic proposal for the formation of the pyrazine 19 upon thermolysis of 2,4-diphenyl-2-oxazolin-5-on (4b, Scheme 7).

Notizen: Exo- and endo-Tricarbonyliron Complexes of Bicyclic 2,3-Dimethylidene Compounds.The preparation of exo- and endo-tricarbonyliron complexes (exo- and endo-5, -6, -8, and 9) of 2,3-dimethylidene-5-bicyclo[2.2.1]heptene(1), -bicyclo[2.2.1]-heptane (2), -5-bicyclo[2.2.2]octene (3) and -bicyclo[2.2.2]octane (4) is described. The complexes are obtained by thermal reaction of the bicyclic butadienes with di-ironenneacarbonyl in hexane solution. exo- and endo-5 are also formed photochemically from ironpentacarbonyl and 1 in pentane solution at -35°. The structural assignment of exo- and endo-5 and -6 is based on their mass-spectra and on coordination shifts in 1H- and 13C-NMR.-spectra exo- and endo-6 are correlated with exo- and endo-5, respectively, by hydrogenation. Hydrogenation of the uncomplexed double bond in exo- and endo-5 occurs in both complexes from the exo side as shown by deuteration experiments. The free ligand 1 reacts in the same stereospecific manner.

Notizen: Photochemical Cyclization of o-, m-, p-Allylanisoles and o-AllylanilinesThe compounds irradiated are summarized in Scheme 1. 2-Allylaniline and N-Alkyl Derivatives. Irradiation (ca. 3 h) of compounds 1-3 with a high pressure mercury lamp in benzene solution under argon (quartz vessel) gave in 40-80% yield the corresponding 2-methylindolines 20, 22 and 25, respectively (Scheme 3). Tetrahydroquinolines (23, 26) were formed only in minor amounts (0,5%). Irradiation in methanol solution yielded in addition to the indolines the 2-(2′-methoxypropyl)-anilines 21,24 and 27, respectively, in a ratio of ca. 0.3, 1.5 and 1.0 with respect to the indolines (Scheme 3). Similar results were obtained in ethanol solution. The observation that the photoreactions in benzene or methanol are not quenched by (E)-piperylene or sensitized by acetone suggests that the transformation starts from the singlet manifold of the aniline chromophor. As outlined in Scheme 11 it is proposed that the excited molecules undergo an intramolecular electron transfer to give an acceptor(olefinic side chain)/donor(aniline part) complex (EDA complex; see [28]) of type {a,b} in which the positive charge is mainly located at the nitrogen atom and the negative charge at C(3′) of the allyl substituent. That the negative charge resides predominantly at C (3′) - independently of alkyl substitution at C (3′) (see experiments cited in [26]) - may be due to electrostatic attraction of the charges. Thus, the following H-transfer occurs almost regiospecifically to give the singlet diradical c which cyclizes directly or via the spirocyclopropane derivative d to the indoline derivative 22. Intermediate d is also responsible for the formation of the 2′-methoxypropyl compounds: It is suggested that in the polar solvent methanol d is partially converted to the zwitterion e, the immediate precursor of 24. Experiments with the deuteriated reactants N-d-2 and 2′-d1-2 (Scheme 3) are in agreement with the proposed mechanism.N, N-Dialkyl-2-allylanilines and Allylanisoles. Upon irradiation in methanol or benzene, these aniline derivatives undergo cyclization to give as the only products the corresponding 2-cyclopropylanilines in 50-70% yield (Scheme 4). 2-, 3- and 4- allylated anisoles behave in the same way on irradiation (Schemes 6-8) as long as the allyl group carries no substituent (CH3, Cl) at the double bond (Schemes 9, 10). No photolytic cyclopropane ring formation is observed with the naphthalene derivatives 7, 8, 17 or 18 (Scheme 1). Experiments with the deuteriated compounds 2′-d1-4 and 1′, 1′-d2-11 - synthesized according to Scheme 2 - indicate that in all cases the cyclopropane formation occurs with concomitant 1,2 aryl migration (Schemes 5, 6) which characterizes the reaction as an aromatic di-π-methane rearrangement (Scheme 14). In contrast to the photoreactions described above the cyclopropane ring formation can be sensitized by acetone or quenched totally by (E)-piperylene. A comparison of the triplet energies (ET) of the aromatic and olefinic chromophor of the reactants (cf. Table 4) shows that the di-π-methane rearrangement is only effective when ET of the aryl part is lower than that of the olefinic part, but not by more than 20 kcal/mol. In substrates carrying substituents at the olefinic double bond the energy of T1 of the allyl group drops beneath that of the aryl part. In these cases no di-π-methane rearrangement is observed because an effective deactivation of T1 of the aryl part occurs by (E)/(Z) isomerization of the side chain as is demonstrated by the photochemical behaviour of compound 10 (Scheme 10). This concept seems to be of general significance for related di-π-methane rearrangements in cyclic systems (cf. Scheme 16; further examples: Scheme 15).