A Serendipitous Synthesis of (+)-Gregatin B, Second Structure Revisions of the Aspertetronins, Gregatins, and Graminin A, Structure Revision of the Penicilliols

A (DHQN)(2)AQN-promoted asymmetric dihydroxylation (92% ee) of the allyl chloride derived from enynol (E)-13 and an 8-step sequence provided access to the hydroxyethylated furanone (R)-21. Oxidation with MnO(2) furnished 50% furanone (+)-(R)-2a and 2.7% isomeric furanone (+)-(R)-3a. (R)-2a possesses the accepted constitution of (+)-gregatin B but its spectra are different. Surprisingly, (+)-(R)-3a equals the natural product. Analogous structure reassignments are due for the gregatins A and C-E, the aspertetronins A-B, graminin A, and the penicilliols A and B.