Thionation reactions of diacylketene thioacetals with the Lawesson reagent and analogues

Abstract

Attempted thionation of diacylketene thioacetals derived from dimedone with dithiadiphosphetane disulphides (the Lawesson reagent and analogues) led to the expected monothioacylketene thioacetals only when the thioacetal sulphur atoms formed part of a dithiolane or dithiane ring. Acyclic analogues readily underwent dealkylation and further reactions, giving a 1,2-dithiole-3-thione derivative as the main isolated product. Reaction of an acyclic ketene thioacetal with P₄S₁₀–Et₃N in acetonitrile at –30 °C permitted the isolation of the primary dealkylation product, a dimedonedithiocarboxylate, in 44% yield. A phenoxaphosphorine derivative was isolated as a by-product in the synthesis of bis(phenoxyphenyl)dithiaphosphetane disulphide.