Stereochemistry of epoxidation and hydroboration of some 4,4-dimethyl-A-homo-5-cholestene derivatives

Abstract

Stereochemistry of epoxidation and hydroboration of some 3-substituted 4,4-dimethyl-A-homo-5-cholestene derivatives was studied. These reactions afforded predominantly products of addition from the less hindered β-side of the cyclic system. Reduction of the 5β,6β-epoxide ring in the 3β-acetoxy derivative IV led to product of diaxial opening, i.e. the 3β,6β-diol VII, whereas in the case of the 3α-acetoxy derivative XIV the reductive as well as alkaline opening of the 5β,6β-epoxide afforded product of 5(O)n participation of the 3α-substituent, i.e. the 3α,5α-transannular epoxide XV.