Total synthesis of the supposed structure of (-)-sclerophytin A and an improved route to (-)-7-deacetoxyalcyonin acetate.

[reaction: see text]Stereoselective acid-catalyzed rearrangement of 15-->16 is the central step in total syntheses of (-)-7-deacetoxyalcyonin acetate (1) and the compound with the alleged structure of sclerophytin A (2). Since tetracyclic diether 2 is not identical to sclerophytin A, the structure of this antineoplastic marine diterpene must be revised. The conversion of 15-->16 demonstrates for the first time that tetrahydrofurans containing (Z)-1-methylalkenyl side chains can be prepared by Prins-pinacol rearrangements.