Bisulfite-mediated base-free decarboxylative carbonylsulfination of alkenes: access to β-keto sultines

A straightforward three-component decarboxylative cross-coupling of α-keto acids, alkenes and sodium bisulfite is established for the construction of otherwise challenging-to-access β-keto sultine derivatives. This reaction involves the photoinduced carbonylsulfination of alkenes and utilizes sodium bisulfite as both a sulfur dioxide surrogate and buffer agent for deprotonation of α-keto carboxylic acids. Of note, the practical procedure featured broad substrate scope and group tolerance for diverse biologically important molecules under mild and operationally simple conditions, using an organic photocatalyst. Mechanistic studies indicated that the transformation proceeds an apparent two-pronged radical addition/radical-polar crossover/SO₂ insertion/ionic cyclization relay process, distinct from traditional alkenes bifunctionalization.