Visible-light-promoted Construction Of C(sp~2)-S Bonds

The C-S bond formation plays an important role in natural products,drug molecules and functional materials.In recent years,much attention has been paid to the visible-light-promoted formation of C-S bonds.The exogenous photosensitizer-,metal-,and base-free visible-light-promoted C(sp2)-H thiolation and visible-light-induced aerobic C(sp2)-H thiocyanation enabled by the in-situ formed copper photocatalysis have been developed.Visible-light-driven,intramolecular C(sp2)-H thiolation has been achieved without addition of a photosensitizer,metal catalyst,or base.This reaction induces the cyclization of thiobenzanilides to benzothiazoles.This cyclization is compatible with a wide range of functional groups.The substrate absorbs visible light,and its excited state undergoes a reverse hydrogen-atom transfer(RHAT)with 2,2,6,6-tetramethylpiperidine N-oxyl to form a sulfur radical.The addition of the sulfur radical to the benzene ring gives an aryl radical,which then rearomatizes to benzothiazole via RHAT.An exogenous photosensitizer free visible-light-mediated oxidative C(sp2)-H thiocyanation of(hetero)arenes in the presence of CuCl2·2H2O using molecular oxygen as the terminal oxidant has been developed.The thiocyanation reaction works for a variety of indoles,anilines and phenols and is suitable for the gram-scale reaction.Mechanism investigation indicates that the formation of a visible light responsive complex[Cu(NCS)2]-is responsible for the occurrence of the aerobic C(sp2)-H thiocyanation.