Synthesis of a Lactone Diastereomer of the Cembranolide Uprolide D

A convergent stereoselective synthesis of a C1/C14 bis-epimer of uprolide D is described in which an intramolecular Barbier-type reaction was employed for macrocyclization with concomitant introduction of the C1 and C14 stereocenters of a fused α-methylene lactone ring through an anti-Felkin−Anh transition state. Unlike previous examples of allyl chromium additions, none of the Felkin−Anh derived adduct could be detected.