Triterpenoid 2,3-ketols, diols and their acetates: Preparation and conformation of the ring A

Abstract

19β,28-Epoxy-18α-oleanane derivatives I-III were converted into hydroxy ketones IV, VIII and X, acetoxy ketones V, VII, IX and XI, diols and their mono- and diacetates XII-XXV. Seven of the eight possible isomeric 2,3-diol monoacetates were obtained. Conformation of the ring A in these compounds has been derived from the 1H NMR and IR spectra. In 2β-acetoxy-3-ketone VII, 3α-hydroxy- and 3α-acetoxy-2-ketones VIII and IX, and in 2β,3α-diol monoacetates XVIII and XIX the ring A exists predominantly in a boat conformation.