Acetolytic cleavage of the epimeric 2- and 6-methoxy-5α-cholestanes involving a 1,2-hydride shift to C-2

Abstract

Acetolytic cleavage of 2β-methoxy-5α-cholestane with boron trifluoride in acetic anhydride followed by hydrolysis gave 5α-cholestan-3α-ol as the major non-olefinic product along with some of the epimeric 2-ols. 2α-Methoxy-5α-cholestane gave 5α-cholestan-2α-ol as the major non-olefinic product, with some 2β-ol and the rearrangement product, 5α-cholestan-3α-ol. Deuterium exchange studies showed that hydride shifts of both 3α- and 3β-hydrogen atoms were involved in the formation of 5α-cholestan-3α-ol from both ethers.

Similar cleavage of 6α-methoxy-5α-cholestane gave only 5α-cholestan-6α-ol, probably formed by nucleophilic attack at the methoxy carbon atom. 6β-Methoxy-5α-cholestane gave only cholest-5-ene.