Studies Directed toward Synthesis of Quassinoids. III. Selective Hydrolysis of the 3α-Acetate Functional Group of Cholic Acid Derivatives

Abstract

Abstract Selective hydrolysis of the 3α-acetoxy group in 5 β-steroid systems with methanolic HC1 prepared by adding acetyl chloride to absolute CH3OH provides a simple and general method for removing the 3α-acetate ester group in diverse derivatives of cholic acid. This hydrolysis of the 3α-acetoxy group by trans-esterification by methanol is faster than methyl esterification of the 23- or 24-oic acid group. The rate of hydrolysis of various acetate groups is in decreasing order of 3α > 17β > 7α,12α. Applications of this method to hydrolysis of the 3α-acetoxy-δ-lactone 14 results in first ring opening of the δ-lactone system before acetate cleavage and provides additional stereochemical evidence for ring A and C having chair conformations and ring B possessing a boat conformation.