Methanolysis of 1-aryl-1,2-epoxycyclohexanes in the condensed and in the gas phase: importance of the substituent for the reaction mechanism

The stereoselectivity of a series of 1-aryl-1,2-epoxycyclohexanes substituted on the phenyl group was determined in acid methanolysis in the condensed phase (0.2N H2SO4-MeOH) and in the reaction with MeOH in the gas phase under catalysis by a gaseous Bronsted acid (D-3(+)). The results obtained show the presence of a clear Hammett-type dependence of the syn/anti adduct ratio on the Brown sigma(+) of the substituent on the phenyl group, thus continuing the validity of the ion-dipole pair mechanism in order to rationalize the stereochemical behavior of 2-aryloxiranes in opening reactions under acidic conditions. Only in the cases of the p-OMe- and p-NO2-substituted epoxides, does an S(N)1 and an S(N)2 process, respectively, appear to be involved. Copyright (c) 2004 John Wiley T Sons, Ltd.