Diels–Alder Reactions of γ-Hydroxybutenolides: Approach to the Himbacine Tricyclic Core

The Diels–Alder reaction of γ-hydroxybutenolides with dienes gave good yields of cycloadducts under thermal and Lewis acid catalyzed conditions. The application of this methodology to a more complex system was demonstrated by the synthesis of a model system for the tricyclic himbacine core. The stereo- and regioselective Diels–Alder reaction established three of the stereogenic centers, with the fourth stereogenic center secured by diastereoselective alkylation of the cycloadduct.