Steric inhibition of resonance and regio- and stereoselectivity in the ring opening of 1-arylsubstituted epoxides : Reactions of 1-phenyl-2,2-dimethyl-7-oxabicyclo[4.1.0]heptane under acidic conditions

The results of the ring opening of 1-phenyl-2,2-dimethyl-7-oxabicyclo4.1.0]heptane (2) under acidic conditions show a marked diminution in the regioselectivity and in the cis stereoselectivity with respect to the corresponding non-methylated epoxide. The percentage composition of the reaction products of epoxide 2 varies significantly with the solvent medium employed. Possible explanations of the observed stereochemical results, particularly with respect to the steric inhibition of resonance of the intermediate carbocation and to the solvent effects, are discussed.