Asymmetric synthesis of polyacetate derived building blocks with alpha-oxyanion functionality. Lewis acid catalyzed opening of 2,9-dioxabicyclo[3.3.1]nonan-3-ones

All four stereoisomeric cyclic 3,5,7-trihydroxyheptanoic acid equivalents o f the polyacetate aldol type (Scheme 1) are obtainable from 8-oxabicyclo[3. 2.1]octd-en-3-one which functions as a meso-configurated 4-way optical swit ch. Lewis acid assisted nucleophilic ring opening of anomeric [3.3.1] oxabi cyclic lactones is a key step. The utility of the methodology is exemplifie d by a 6 step synthesis of the C17-C23 fragment of spongistatin (altohyrtin ) and C-glycoside analogues. (C) 1999 Elsevier Science Ltd. All rights rese rved.