Approaches to the Synthesis of Triterpenoids. II. Some Tetracyclic Precursors Suitable for Conversion into Pentacyclic Triterpenoids

Abstract

The stereoselective total synthesis of several partially reduced chrysene derivatives, suitable as precursors for a variety of triterpenoids, is described. The key reaction in the most efficient route involves the highly stereoselective reductive alkylation of a cyclic α,β-unsaturated ketone with allyl bromide in lithium–ammonia, using water as a proton donor.