Total Synthesis and the Confirmation of the Revised Structures of Botcinins A and B

The stereoselective total syntheses of botcinins A (1) and B (2), and homobotcinin E (4), a homologue of botcinin E (3), have been achieved starting from a polyoxygenated tetrahydropyran intermediate 15 via formation of botcinic acid (12) and botcineric acid (13). Through the total syntheses, three actual relationships are revealed, that is, (i) the structure of botcinin A (1) is identical with the revised structure of the natural compound, which was formerly assumed to be 3-O-acetyl-2-epibotcinolide (5), (ii) the structure of botcinin B (2) is identical with the revised structure of the natural compound, which was supposed to be 3-O-acetyl-2-epihomobotcinolide (6), and (iii) the structure of the natural compound formerly assumed to be 2-epihomobotcinolide (8) must be revised to that of homobotcinin E (4).