An Approach Toward the Total Synthesis of C16 Tetranorditerpenoids Norcrassin A and Norcrocrassinone: Synthesis of the BC-Ring System

Abstract

Norcrassin A and norcrocrassinone are C16 tetranorditerpenoids featuring unique polycyclic frameworks. Herein, we detail a seven-step synthesis of the BC-bicyclic lactone common to both natural products. Key reactions include a SO3-mediated allylic alcohol transposition, Johnson–Claisen rearrangement, and an epoxide ring-opening/lactonization sequence.