Short Approach toward the Nonracemic A,B,E Tricyclic Core of Calyciphylline B-Type Alkaloids.

A suitably functionalized tricyclic adduct containing the common A,B,E rings found in calyciphylline B-type alkaloids was obtained in nine linear steps. The key transformation features an efficient one-pot sequence of intramolecular Vilsmeier–Haack cyclization and azomethine ylide 1,3-dipolar cycloaddition in which three cycles, three new carbon–carbon bonds, and three stereocenters are formed, one being fully substituted. This work also demonstrates the first use of a chiral, nonracemic cyclic enol ether as an internal carbon nucleophile.