Synthesis of spiroepoxynucleosides

Abstract

The first syntheses of spiroepoxyhexopyranosyl-purines and -pyrimidines are reported. The spiro epoxy group was introduced at C-2′ by treatment of 2′-keto-β-L-nucleosides with dimethylsulphoxonium methylide. Addition of the sulphur ylide generated from Me₃SOCI and NaH afforded β-L-talo- and β-L-galacto-spironucleosides. Interestingly, when trimethylsulphoxonium chloride was activated with butyl-lithium, an inversion took place at C-1′ leading exclusively to an α-L-galacto-spironucleoside.