Transition-Metal-Free and Photocatalyst-Free Sulfenylation of Halopyrazolamines under Visible-Light Irradiation via Electron Donor–Acceptor Complexes

Abstract

AbstractA new approach was developed for the thiolation of halogenated pyrazole-5-amines under blue LED irradiation in metal-free conditions. This efficient and practical approach enabled the generation of thiolated pyrazol-5-amine building blocks of medicinal significance. This straightforward technique permits photochemical thiolation by an electron donor–acceptor by two distinct processes; formation of a charge-transfer complex through a halogen bond or π–π interaction based on various halogenated pyrazolamines, depending on the HOMO–LUMO energy gap of the C–X bond. The reaction of halogenated pyrazol-5-amines with thiophenol derivatives proceeded in good to excellent yields. The formation of a π–π complex or halogen bonding between the halopyrazolamine and the thiolate anion was confirmed by UV/visible spectroscopy.