Stereocontrolled Preparation of the C1-C14 Polyene Fragment of Benzenic Ansamycin Antibiotics Ansatrienin A and B

Abstract

A practical synthesis of the C1-C14 polyene unit 5 in ansatrienin A (mycotrien I), 1a, and other ansamycin antibiotics is described which involves elaboration of the chiral unsaturated aldehyde 6 and phosphonate 7, followed by coupling of the building blocks by Horner-Emmons-olefination and Duthaler's aldolation. The synthesis of 6 successfully applies two consecutive Evans-aldol reactions for constructing the carbon backbone.