Neighbouring group effects. Part 2. Effect of epoxide on the hydrolysis of adjacent acetate groups

Abstract

The presence of an epoxide at the 4,5-position of a steroid accelerates the hydrolysis of an acetate group at the 3β- or 6β-positions. This effect is also observed for a 1α-acetoxy-2β,3β-epoxide. A suitable fixed dipole–dipole orientation between the ester group and the adjacent polar group may be an important factor in the rate acceleration, since this neighbouring effect does not occur when a non-rigid side chain is present. Fluorine or bromine substitution at the 5α-position also enhances the rate of hydrolysis of a 6β-acetoxy-group.