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

Abstract

Under blue LED irradiation and metal-free conditions, a new approach for the thiolation of halogenated pyrazole-5-amine was developed. This efficient and practical approach enabled the generation of thiolated pyrazole-5-amine building blocks of medicinal significance. This straightforward technique reveals photochemical thiolation by an EDA complex via two distinct processes. The formation of the charge transfer complex via a halogen bond or a π-π interaction is based on various halogenated pyrazole amines following the HOMO-LUMO energy gap of the C-X bond. The scope of reaction with halogenated pyrazole-5-amines and thiophenol derivatives obtained in good to excellent yields. The formation of the π-π complex or halogen bonding between halo-pyrazole amine and thiolate anion was confirmed by UV-visible spectroscopy measurements