Stereochemical aspects in the 4-vinylcyclohexene biotransformation with rat liver microsomes and purified cytochrome P450s: diepoxide formation and hydrolysis.

The stereochemical course of the biotransformation of 1,2-monoepoxides of 4-vinylcyclohexene (2 and 3) by liver microsomes from control and induced rats and by purified P4502B1 and P4502E1 has been determined. The epoxidation of monoexpodies cis-4-vinylcyclohexene 1,2-epoxide (2) and trans-4-vinylcyclohexene 1,2-epoxide (3) gives the corresponding eight isomeric diepoxides cis-4-vinylcyclohexene diepoxide (9) and trans-4-vinylcyclohexene diepoxide (10). The stereoselectivity of this process is affected by P450 induction.

Reactivity of homoallylic substituted adamantylideneadamantanes with bromine. Substituent effects on the stability of the ionic and nonionic intermediates.

Sterically congested adamantylideneadamantanes (1b-g) (X = Br, Cl, F, OH, OEt, OCOCH(3)), homoallylically substituted with equatorial groups (X), react with bromine in 1,2-dichloroethane to give a stable bromonium ion intermediate or a substitution product depending on the nature of the substituent and on the bromine concentration. The nature of the substituent markedly affects the formation constant of the 1:1 pi-complexes, as well as of the formation constant and reactivity of bromonium ion intermediates. The different reactivity of the ionic intermediates, which depends on the nature of substituents, is attributed to bromonium or bromocarbenium character of the intermediate, with the support of theoretical investigations.

Strain and reactivity: electrophilic addition of bromine and tribromide salts to cyclic allenes.

The kinetics and the products of the bromination of several cyclic allenes, from C(9) to C(13) (1 a-e), with tetrabutylammonium tribromide (TBAT) and Br(2) have been investigated in 1,2-dichloroethane (DCE) and methanol. The first product of the interaction between the allene and Br(2) is a 1:1 pi complex. The stability constant of this complex, determined at 25 degrees C for allene 1 a, is 7.