Enantioselective Synthesis of the Hydroazulene Core of 3α‐Hydroxy‐15‐rippertene

Abstract

Abstract As part of a project directed toward the total synthesis of the tetracyclic diterpene 3α‐hydroxy‐15‐rippertene, a constituent of the defense secretion of higher termites, a fast access to two advanced hydroazulene key intermediates has been achieved by starting from (–)‐isopulegol. A regio‐ and diastereoselective formal hydromethallylation and a regioselective ring expansion served as the key steps in the formation of the seven‐membered ring. Completion of the bicyclic title compounds was then achieved by cyclopentene annulation through diastereoselective conjugate addition of organocuprates and subsequent intramolecular aldol condensations.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)