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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).

The α-hydroxy-α-methyl-β-hydroxy units are enantioselectively prepared by way of asymmetric aldol reactions between both achiral β,β- disubstituted silyl enolates and aldehydes. (-)-2-C-Methyl-D-threono-1,4-lactone is conveniently synthesized by using this reaction