Visible Light-Induced Energy Transfer Mediated Regioselective C-3 Thiolation of Imidazoheterocycles using Bunte Salts.

Abstract

An external-photocatalyst-free visible light-induced regioselective C-3 sulfenylation of imidazo[1,2-a]pyridines using Bunte salts has been accomplished via C(sp2)-H functionalization. This protocol allows the coupling of a wide range of imidazoheterocycles with alkyl-, benzyl-, and aryl Bunte salts under ambient air as the sole oxidant. The radical scavenging, UV-visible spectroscopic studies, and Stern‒Volmer experiments revealed that the reaction occurs through energy transfer followed by a radical SET pathway. In this work, the dual role of imidazopyridines as photoexciting species and as energy transfer vehicle is proposed. Activation of the triplet oxygen as a result of energy transfer, which acts on somophlic Bunte salts to generate thiyl radical, eventually resulting in the C(sp2)-H functionalization.