Approach to the synthesis of spiroiridal-type triterpenoids via an Ireland-Claisen rearrangement

Abstract

The formation of carbon-carbon bonds in an asymmetric manner is a central goal of modern synthetic chemistry. Many methods have been developed to form a variety of linkages and substitutions, however the asymmetric formation of quaternary carbons of spirocycles is still a formidable challenge. These compounds represent special challenges because of the requirement of double ring formation together with the control of facial selectivity during the formation of a quaternary carbon centre. The present work demonstrates our efforts towards establishing a strategy based on the Ireland-Claisen rearrangement as the key step for the synthesis of the quaternary spiro-fused ring system such as those found in iridal triterpenoids. 28-Deacetylbelamcandal, a spiroiridal-type triterpenoid, is a representative compound found in iridaceous plants and shows important biological activities in tumor promotion. The synthesis of this compound has been planned from the methodology currently in progress in our group.