Total Synthesis and Structural Revision of (+)-Yaoshanenolide B.

(+)-Yaoshanenolide B was synthesized employing as a key step an endo- and face-selective Diels-Alder reaction between natural R-(-)-α-phellandrene and the exocyclic double bond of a 5-methylene-2(5H)-furanone. The dienophile furanone was prepared by photooxygenation of a suitably substituted 2-thiophenylfuran followed by dehydration of the resulting γ-hydroxybutenolide. Through this synthesis, the initially proposed structure for (+)-yaoshanenolide B has been revised to the 1R,2S,4R,7R,1″S diastereomer.