Asymmetric total synthesis of cephanolide B

The asymmetric synthesis of cephanolide B, a complex C18 Cephalotaxus dinorditerpenoid, is presented for the first time. The synthesis relies on the key hexahydrofluorenone core skeleton (A-B-C ring). A remote hydroxyl group directed hydrogenation strategy was developed to selectively reduce the tetra-substituted enone unit. A sequence of modified transformations, including single electron reduction, Barton-McCombie radical deoxygenation, lactonization, and cation mediated Friedel-Crafts cyclization, were efficiently employed to achieve the target.