Total Synthesis of Cochlearol B via Intramolecular [2+2] Photocycloaddition.

Herein, we describe the first total synthesis of cochlearol B, a meroterpenoid natural product featuring a 4/5/6/6/6-fused pentacyclic structure. Key steps, oxidative cyclization and subsequent intramolecular [2+2] photocycloaddition, which constructed the pentacyclic structure in highly stereoselective manner, allowed efficient access to cochlearol B with the longest linear sequence of 16 steps, and in 9 % overall yield. Single-crystal X-ray crystallographic analysis clearly confirmed the stereochemistry of cochlearol B.