A ketal Claisen rearrangement for α-ketol isoprene unit elongation: application to a practical synthesis of sarcophytol A intermediate

Abstract

A new ketal Claisen rearrangement using the ketal 10 for the isoprene unit elongation which affords terminal α-ketol terpenoid is presented. Its efficiency is demonstrated by successful transformation of the product of this reaction, the α-ketol 20, into 2, the acyclic precursor of sarcophytol A total synthesis, by two alternative routes via the β,γ-unsaturated aldehyde 24 and the allylic alcohol 28.