Phorboxazole Synthetic Studies. 1. Construction of a C(3−19) Subtarget Exploiting an Extension of the Petasis−Ferrier Rearrangement

Abstract
In this, the first of two Letters, we outline our overall strategy for the total synthesis of phorboxazoles A (1) and B (2), rare oxazole-containing macrolides possessing extraordinary antimitotic activity, and describe the assembly of a C(3−19) subtarget (−)-5 for the total synthesis of phorboxazole A. The synthesis of (−)-5 was achieved in 15 linear steps (12% overall yield), exploiting a modification of the Petasis−Ferrier rearrangement to construct the C(11−15) cis-tetrahydropyran. Dimethylaluminum chloride (Me2AlCl) proved to be the Lewis acid of choice for the Petasis−Ferrier rearrangement.