- ETUDE DE L'HYDROGENATION DE L'α-TERPINENE ET DU DIHYDRO-2,3 ANISOLE CATALYSEE PAR LE PHENANTHRENE CHROME TRICARBONYLE
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The hydrogenation of α-terpinene and 2,3-dihydroanisole catalysed by phenanthrenechromium tricarbonyl in cyclohexane is described.The catalytic reaction is accelerated when small amount of ketone are added to the solution.Attempts to induce asymmetric syn
- Maux, P.Le,Dabard, R.,Simonneaux, G.
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- Direct evidence for anchimeric assistance in alcohol elimination from gas-phase MH+ ions of 1,4-dialkoxycyclohexanes under chemical ionisation. Experiment and theory
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trans-1,4-Dialkoxycyclohexanes afford very abundant [MH - ROH]+ ions upon chemical ionisation (CI), in contrast to the cis-isomers, suggesting anchimeric assistance in the alcohol elimination from the MH+ ions of the trans-diethers. Collision induced dissociation (CID) measurements of the [MH - ROH]+ ions, obtained from various suitably deuterium labelled stereoisomeric 1-ethoxy-4-methoxycyclohexanes, indicated fromation of symmetrical bicyclic ethyl and methyl oxonium ions by an anchimerically assisted alcohol elimination from the trans-diethers. On the other hand these measurements suggest that the cis-isomers afford isomeric monocyclic O-protonated 4-alkoxycyclohexene cations, in which the hydrogens at positions 2 and 3 (as well as those at positions 5 and 6, and 1 and 4) are not equivalent. The two results, namely the symmetrical bicyclic structure and the high abundance of the [MH - ROH]+ ions in the CI mass spectra of the trans-diethers, in contrast to the non-symmetrical monocyclic structure and low abundance of these ions in the cis-isomers, are suggested to be direct evidence for anchimeric assistance in a gas-phase ion dissociation process. Ab initio calculations at the MP3/6-31G*//6-31G* level support the anchimerically assisted elimination mechanism observed in trans-1-ethoxy-4-methoxycyclohexane, but also show that the energy difference between the anchimerically assisted and non-assisted elimination mechanisms is small (ca. 2-3 kcal mol-1)(1 cal = 4.184 J).
- Shvily, Ronit,Mueller, Thomas,Apeloig, Yitzhak,Mandelbaum, Asher
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p. 1221 - 1234
(2007/10/03)
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- Three Component Reactions. XX. Methoxymercuration of Cyclohexa-1,4-dienes
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The methoxymercuration of several cyclohexa-1,4-dienes leads to insoluble mixtures of mono- and bismercuricompounds 2-4 and 5-7.After reduction with NaBH4/NaOH mixtures of methoxycyclohexenes and bismethoxycyclohexanes result.The result of capillary gaschromatographic analyses and n.m.r. spectra allows a semiquantitative evaluation of the reaction pathways.
- Beger, J.,Thomas, B.,Vogel, T.,Lang, R.
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p. 447 - 453
(2007/10/02)
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- Deamination Reactions, 51. - Decomposition of Bicyclohexane-exo-6-diazonium Ions
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The nitrous acid deamination of the amine 13, the copper(II)-induced cleavage of the nitrosourea 19, and the thermolysis of the nitrosoamide 20 were used to generate the diazonium ion 7.In contrast to previous work, performed in the presence of base, the neutral to weakly acidic conditions of the present study afforded substantial fractions (30-40percent) of bicyclohex-exo-6-yl products (15).Small quantities of bicyclohex-endo-6-yl (14), bicyclohex-2-yl (25, 26) and 3-cyclohexen-1-yl (27) derivatives were also detected, the latter arising by a 1,3-hydride shift.These results, unprecedented with higher homologs of 7, suggest a largely "classical" bicyclohex-6-yl cation (21) as the initially formed intermediate.Capture of 21 is thought to compete with disrotatory transformation to the cyclohexenyl cation 12. - Keywords: Bicyclohex-6-yl derivatives/ Diazonium ions/ Electrocyclic reactions/ Nucleophilic displacement
- Kirmse, Wolfgang,Hellwig, Georg
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p. 389 - 392
(2007/10/02)
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- Factors Influencing Conformational Preferences in Cyclohexenes
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Conformational preferences have been measured for the first time for 4-substituted cyclohexenes in a solvent of low polarity.Measurements were made for the substituents Cl, Br, I, OH, OSiMe3, and CN and were compared with conformational preferences in cyclohexyl and exo-methylenecyclohex-3-yl.In the nearly nonpolar solvent CF2Cl2, in which intramolecular interactions are maximized, there is a much larger axial population for cyclohexen-4-yl than in cyclohexyl or exo-methylenecyclohex-3-yl.In particular, the dipolar interaction of the endocyclic double bond is reduced from that of the exocyclic double bond.This observation is confirmed by the almost negligible effect of symmetrizing the endocyclic double bond through 1,2-dimethyl substitution, in contrast with the large effect of symmetrizing the exocyclic double bond through 7,7-dimethyl substitution.Polar solvents increase the proportion of the axial conformer to a smaller extent for the endocyclic than for the exocyclic system, again in agreement with a lower dipolar effect in the endocyclic case.These results emphasize the anisotropic nature of the steric effects of double bonds.
- Lambert, Joseph B.,Marko, Dale E.
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p. 7978 - 7982
(2007/10/02)
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- CATALYTIC HYDROGENATION OF α-TERPINENE AND 2,3-DIHYDROANISOLE BY A PHENANTHERENECHROMIUM TRICARBONYL COMPLEX
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The hydrogenation of α-terpinene and 2,3-dihydroanisole catalysed by phenanthrenechromium tricarbonyl is described and discussed.
- Maux, Paul Le,Simonneaux, Gerard
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p. C24 - C26
(2007/10/02)
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