Synthesis of the stemodane carbon skeleton: nonstereoselective photoaddition of allene to a cyclopentenone and a novel rearrangement reaction

Abstract

The tetracyclic dione (21), possessing the stemodane carbon skeleton, is obtained via an 8-step synthetic sequence from the tricyclic enone (3); the most interesting steps of the overall conversion involve the nonstereoselective photoaddition of allene to (3), and the transformation of both of the resultant adducts (4) and (5) into a single keto ester (10).