Synthetic Studies on the Bryostatins:  Preparation of a Truncated BC-Ring Intermediate by Pyran Annulation

A synthesis of a potential BC-ring subunit (C₉−C₂₇) for bryostatin 1, a remarkably potent anticancer agent, has been developed in 16 steps and 18% overall yield. The key features of this route include a BITIP-catalyzed asymmetric allylation reaction, chelation-controlled allylations, a hydroformylation reaction, and a pyran annulation reaction.