An efficient formal synthesis of hyphodermin B 1, a metabolite of Hyphoderma radula, has been completed in 15% overall yield. The tricyclic carbon skeleton 3 was rapidly assembled from a novel vinyl enone via a Diels-Alder reaction, followed by dehydrogenation and anhydride formation. Selective reduction of anhydride 3 with LiAlH(t-BuO)3 gave hyphodermin B 1 in 99% yield. The structure of hyphodermin B 1 was confirmed by X-ray crystallographic analysis. The anhydride 3, bearing a ?-carbonyl group, displayed unexpected reactivity with the anhydride carbonyl closest to the ?-ketone being the most electrophilic site. This was confirmed by HF/6-31G* calculations. In the presence of base, 3 underwent a rearrangement to the novel lactone 16.