Formal synthesis of (+)-brefeldin A: application of a zinc-mediated ring expansion reaction.

An efficient formal synthesis of (+)-brefeldin A was accomplished through a synthetic approach that relied upon three keys steps. The five-membered ring was generated in a stereocontrolled fashion through application of a tandem conjugate addition-intramolecular cyclization method developed by Toru. Ring-closing metathesis provided access to a twelve-membered beta-keto lactone, which was ring-expanded to the alpha,beta-unsaturated-gamma-keto lactone through a zinc carbenoid-mediated reaction. Conversion of this lactone to (+)-brefeldin A has been reported previously.