Chemoenzymatic Total Syntheses of Ribisins A, B, and D, Polyoxygenated Benzofuran Derivatives Displaying NGF-Potentiating Properties

Total syntheses of the structures, 1, 2, and 4, assigned to the biologically active natural products ribisins A, B, and D, respectively, have been achieved using the microbially derived and enantiomerically pure cis-1,2-dihydrocatechol 5 as starting material. Key steps include Suzuki–Miyaura cross-coupling, intramolecular Mitsunobu, and tandem epoxidation/rearrangement reactions. As a result of these studies, the structures of ribisins A and D have been confirmed while that of congener B was shown to be represented by 31 rather than 2.