Sulfur Betaines from S-Propargyl XanthatesUnusual Chemistry from a Simple Functional Group

S-Propargyl xanthates undergo upon heating a [3,3] sigmatropic rearrangement followed by a reversible ring closure into a novel betaine. This betaine can be implicated in carbon-carbon bond forming processes, in the synthesis of esters, in the inversion of secondary alcohols, in the formation of alkenes, for the generation of rigid, cisoid dienes that are highly reactive in both inter- and intra-molecular Diels-Alder cycloadditions, and in various other synthetically useful transformations. 1 Introduction 2 An Unexpected Transformation 3 Evidence for the Betaine Intermediate 4 A Method for the Synthesis of Esters and for the Inversion of Secondary Alcohols 5 A General Alkylation Process 6 The Case of Carbon Acids 7 A Synthesis of Alkenes 8 Further Trapping Experiments. Concerted or Not Concerted? 9 Rigid Cisoid Dienes 10 Propargyl Radicals 11 Concluding Remarks.