Decarboxylative Photoadditions of Heteroatom-substituted Carboxylates to Phthalimides

Abstract

α-Thioalkyl and α-oxoalkyl-substituted potassium carboxylates efficiently decarboxylate in the presence of electronically excited phthalimides. Radical coupling and reduction products result from secondary steps. In contrast, β-thioalkyl-substituted carboxylates are unreactive under the reaction conditions whereas β-oxoalkyl-substituted carboxylates react quantitatively. This behaviour is rationalized by assuming primary photoinduced electron transfer with sulfur oxidation, respectively, and no oxidation of the ether oxygen. In β-thioalkyl-substituted carboxylates, the thioether radical cation serves as hole trap and prevents the carboxylate of oxidative cleavage.