The first transannular [4+3] cycloaddition reaction: synthesis of the ABCD ring structure of cortistatins

A 14-membered macrocycle with an allene and a furan strategically located at across the ring from each other is synthesized using an allene ring closing metathesis reaction. Upon treatment of the macrocycle with a catalytic amount of Pd(OAc)(2) and other additives, the first transannular [4+3] cycloaddition occurred to yield 37% of a tetracyclic compound containing the ABCD ring structure of the natural products cortistatins. (C) 2008 Elsevier Ltd. All rights reserved.