Studies of neodolastanes — Synthesis of the tricyclic core of the trichoaurantianolides

Abstract

Studies toward the synthesis of trichoaurantianolide C (5) are described. Stille cross-coupling reactions of (E)- and (Z)-β-stannyl-α,β-unsaturated esters with allylic acetate 32 provide for the stereocontrolled formation of nonconjugated 2,5-diene-1-ols. Studies of the asymmetric Sharpless epoxidation are utilized to establish diastereofacial selectivity for the preparation of a crucial C2 tertiary allylic alcohol for subsequent esterification and ring-closing metathesis. SmI2 reductive cyclization of the key butenolide precursor 49 led to formation of the central seven-membered ring of the tricyclic core of the natural product.