A concise formal synthesis of bufogargarizin B

Abstract

A concise and scalable formal synthesis of bufogargarizin B has been achieved by completing the synthesis of the advanced [5–7–6–5] tetracyclic intermediate II in 8 steps with 36 % overall yield from commercially available estrone 8. Key features of the synthesis include stereoselective reduction of the carbonyl group and an oxidative cleavage/transannular aldol cascade reaction to rapidly construct the rearranged A/B ring system and three stereogenic centers. This study presents a new synthetic approach to the unique rearranged framework of bufogargarizin B and related steroids.