Tetracyclic triterpenes. Part 15. Ring expansion of steroidal acyloins: 3-acetyl-3-hydroxy-14α-methyl-4-nor-5α- and -5β-cholest-8-ene

Abstract

The base- and acid-catalysed ring A expansion of steroidal acyloins, 3-acetyl-3-hydroxy-14α-methyl-4-nor-5α- and -5β-cholest-8-ene, gave 3,14-dimethyl-4-oxo-5α- and -5β-cholestane derivatives. The regioselective migration of the secondary carbon atom C-3 is explained by the steric factors and conformational preference for the formation of the chair-like transition state.