Total Synthesis of (−)-Angiopterlactone B

An enantioselective total synthesis of (−)-angiopterlactone B has been accomplished in four steps. The synthesis features a proposed biomimetic domino ring-contraction/oxa-Michael/Michael dimerization sequence, forming three new bonds, two new rings, and three new contiguous stereogenic centers in a single step. It has been determined that the originally proposed absolute configuration of natural (+)-angiopterlactone B needs revision. This reveals that angiopteroside, a known glycoside natural product, is the likely biosynthetic precursor to (+)-angiopterlactone B.