PPh₃·HBr-DMSO mediated expedient synthesis of γ-substituted β,γ-unsaturated α-ketomethylthioesters and α-bromo enals: Application to the synthesis of 2-methylsulfanyl-3(2 H)-furanones

An efficient chemoselective general procedure for the synthesis of γ-substituted β,γ-unsaturated α-ketomethylthioesters from α,β-unsaturated ketones has been achieved through an unprecedented PPh₃·HBr-DMSO mediated oxidative bromination and Kornblum oxidation sequence. The newly developed reagent system serves admirably for the synthesis of α-bromoenals from enals. Furthermore, AuCl ₃-catalyzed efficient access to 3(2H)-furanones from the above intermediates under extremely mild conditions are described.