The rearrangement of isothiochroman sulphonium ylides via a thermal ylide exchange reaction

Abstract

The copper-bronze-catalysed decomposition of ethyl diazoacetate in isothiochroman (1) yields mainly ethyl isothiochroman-1-ylacetate (2). The formation of the ester (2) is rationalized in terms of a thermal ylide exchange reaction of the unstable sulphonium ylide initially formed, prior to a Stevens-type rearrangement. Thermal decomposition of the stable bis(ethoxycarbonyl)(isothiochroman-2-io)methanide (6) yields diethyl isothiochroman-1-ylmalonate (8), in support of the above mechanism.