Stereoselective Total Synthesis of Cladospolide A

Abstract

A simple and highly efficient stereoselective total synthesis of cladospolide A, a polyketide natural product, has been achieved. The synthesis involves stereoselective zinc-mediated allylation, pivotal aldol coupling, and ring-closing metathesis. The pivotal aldol coupling is used for the first time for macrolide construction and provides an effective alternative to Yamaguchi macrolactonization.

Key words

stereoselective synthesis - zinc mediator - allylations - aldol coupling - ring-closing metathesis

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18

Acetyl fragment 16 was synthesized (Scheme  [³] ) from commercially available epoxide 15, which was subjected to copper(I) cyanide promoted regioselective nucleophilic ring opening with allylmagnesium chloride to provide the corresponding alcohol in 87% yield; acetylation of the alcohol by use of acetic anhydride and pyridine yielded 16.

Scheme 3 Reagents and conditions: (a) allyl chloride, Mg, CuCN, THF, 0 ˚C to r.t., overnight; (b) Ac₂O, py, 0-25 ˚C, 3 h, 98%.