Epoxide Ring Opening by Dianions Derived from β-Ketosulphones. Synthetic Studies on the 7-Hydroxy-4-oxopropenoate System and Medium-Ring Lactones

Abstract

The nucleophilic ring opening of an epoxide by the dianion derived from a β-ketosulphone is examined. Alkylation of the anion derived from the β-ketosulphone product with ethyl bromoacetate, followed by elimination of sulphinic acid with 1,8-diazabicyclo[5.4.0]undec-7-ene then leads to trans-7-hydroxy-4-oxopropenoates. Utility of this approach to the preparation of natural product systems is illustrated by a formal synthesis of (±)-pyrenophorin. Preparation of the β-ketosulphone intermediates via reaction of the α,α-dilithiodianion derived from phenyl methyl sulphone with various lactones is also examined. This approach is extended to the preparation of 8-, 9-, and 10-ring lactones possessing cis-7-, -8-, and -9-hydroxy-4-oxopropenoate moieties, respectively, by the intramolecular alkylation of β-ketosulphones containing a bromoacetoxy group.