- Hydrocarbures arylaliphatiques. Partie VIII. Etude cinetique de la protodesilylation de benzocyclenes tricycliques
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A kinetic study of the protodesilylation of silylated derivatives of hemimellitene, 2a,3,4,5 tetrahydro acenaphthene and 1H 2,2a,3,4,5,6 hexahydro benzo(c,d)azulene is described.These results complete those published previously and which are related to the influence of the ring size of alicyclic systems pericondensed to a benzene nucleus on the reactivity of the nucleus to acetylation or bromination.The silylated derivatives were prepared from the corresponding bromo compounds.The synthesis of the bromo compounds, some of which were described in an earlier study, is completed here by using a synthetic pathway which allows the preparation of the β isomers starting from the ortho bromo derivatives.The kinetic results show a deactivation of the β position of the hemimellitene.A little deactivation of ortho α position of the five membered ring in the tricyclic compounds is also observed.This last result, significant in the case of bromination, seems to be related to the Mills-Nixon effect and can be explained by using Streitwieser's hybridization for the ? skeleton.
- Gruber, Rene,Kirsch, Gilbert,Cagniant, Denise
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p. 498 - 504
(2007/10/02)
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- "1,4" Alkyl Migrations in Fischer Indole Cyclizations
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The product from Fisher indole cyclization and dehydrogenation of cyclohexanone 2,4,6-trimethylphenylhydrazone (1) was determined to be 2,3,4-trimethylcarbazole (3) resulting from a formal 1,4-methyl migration, as previously proposed.To determine the destinations of migrating groups in these rearrangements, the Fischer indole cyclization and dehydrogenation of cyclohexanone 2-ethyl-6-methylphenylhydrazone (17) were studied.The products obtained were 1-ethylcarbazole, 1-methylcarbazole, 2-ethyl-1-methylcarbazole (18), and an apparent mixture of 1-ethyl-4-methylcarbazole (21) and 4-ethyl-1-methylcarbazole (22).However, no 1-ethyl-2-methylcarbazole (19), which would have been obtained by a "1,4"-methyl migration, was obtained.Analysis of the product ratios suggested that the apparent ethyl shift in formation of 18 actually proceeded by a formal shift of either an ethyl or a methyl group, followed by a ethyl shift.Cyclization of 3-pentanone 2,4,6-trimethylphenylhydrazone (26) proceeded to give the product of "1,4" methyl migration, demonstrating that such reactions can occur with phenylhydrazones of ketones other than cyclohexanone.It is proposed that steric factors play a major role in determining whether migrating groups undergo or "1,4" shifts during Fischer indole cyclizations.
- Miller, Bernard,Matjeka, Edward R.
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p. 4772 - 4780
(2007/10/02)
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