Photochemical cyclization of thioformanilides by chloranil: An approach to 2-substituted benzothiazoles

2-Substituted benzothiazoles were efficiently synthesized by radical cyclization of thioformanilides induced by chloranil under irradiation in 1,2-dichloroethane and toluene at 80 °C. Hydrogen atom abstraction from thiobenzamide by triplet chloranil was the key step of the mechanism, as confirmed by LFP experiments. The methodology developed is simple and afforded the easily isolated products from moderate to good yield.