The chemistry of spiroacetals. Preparation of a chiral disubstituted lactone derivative; a key intermediate for synthesis of the spiroacetal moieties of the avermectins and milbemycins

Abstract

A synthesis of two diprotected (4S, 6S)-4-hydroxy-6-hydroxymethyltetrahydropyran-2-ones has been developed from laevoglucosan; reaction of these lactones with a substituted lithium acetylide derivative followed by hydrogenation and acid catalysed cyclisation has led to formation of the spiroacetal moiety of milbemycin β1 and β3.