Use of Molecular Oxygen as a Reoxidant in the Synthesis of 2-Substituted Benzothiazoles via Palladium-Catalyzed CH Functionalization/Intramolecular CS Bond Formation

Molecular oxygen (O2) was successfully employed as a reoxidant in cyclizations of thiobenzanilides 1a–s through a palladium‐catalyzed CH functionalization/intramolecular CS bond formation process, leading to an efficient, green method for the synthesis of 2‐arylbenzothiazoles 2a–s. Addition of cesium fluoride (CsF) greatly enhanced the reactions, which produced variously substituted 2‐arylbenzothiazoles with good functional group tolerance. Thioureas 4a–j were also found to be suitable substrates for the cyclization process using a palladium/O2 catalyst system, thus generating 2‐aminobenzothiazoles 5a–j. One‐pot syntheses of 2‐aminobenzothiazoles 5a–j from aryl isothiocyanates 6 and amines 7 were also successful.