Chiral 1,4-dicarbonyl-2,3-O-isopropylidene derivatives. Rapid racemizationon standing

1,4-Dicarbonyl-2,3-chiral derivatives are useful synthetic precursors for t he preparation of carbocyclic rings but, in many cases, losses of optical p urity have been reported, 1-Deoxy-3,4-O-isopropylidene-6-O-trityl-D-erythro -hexo-2,5-diulose and 1-deoxy-3,4-O-isopropylidene-6-O-(tert-butyldiphenyls ilyl)-D-erythro-hexo-2,5-diulose were synthesized from D-ribono-1,4-lactone . These compounds were selected to study the epimerizability of 2,3-O-isopr opylidene-1,4-dicarbonyl derivatives. It was found that both compounds smoo thly epimerize and partially racemize on standing. (C) 1999 Elsevier Scienc e Ltd. All rights reserved.