Synthesis of (.+-.)-7,8-Epoxy-4-basmen-6-one by a Transannular Cyclization Strategy

The first synthesis of the cembranoid natural product (±)-7,8-epoxy-4-basmen-6-one (1) is described. Key steps of the synthetic route include the cationic cyclization of the acid chloride from 15 to provide the macrocycle 16, and the photochemical transannular radical cyclization of the ester 41 to form the tricyclic product 50. Product 50 was transformed into 1 in ten steps. Transition-state molecular modeling studies were found to provide accurate predictions of the structural and stereochemical outcomes of cyclization reactions explored experimentally in the development of the synthetic route to 1. These investigations should prove valuable in the development of transannular cyclization as a strategy for synthetic simplification.