I2/K2S2O8-Promoted ring-opening cyclizations of benzothiazoles and 3-oxo-3-arylpropanenitriles

• An efficient I 2 -catalyzed ring expansion of benzo[ d ]thiazole and 3-oxo-3-arylpropanenitrile is described. • A series of 3-aryl-4 H -benzo[ b ][1,4]thiazine-2-carbonitriles were obtained with good yields. • The method is characterized by good functional group tolerance, broad substrate scope as well as gram-scale synthesis. An efficient I 2 /K 2 S 2 O 8 -promoted ring expansion of benzo[ d ]thiazole and 3-oxo-3-arylpropanenitrile has been developed. A variety of benzo[ d ]thiazole derivatives underwent the ring-opening cyclization smoothly to afford the diverse 3-aryl-4 H -benzo[ b ][1,4]thiazine-2-carbonitriles in moderate to excellent yields. This protocol features metal-free reaction conditions, stable and available starting materials, and good group tolerance. The synthetic utility of this protocol was also demonstrated through gram-scale reaction and product derivatization. Mechanism studies indicate that the reaction may undergo a free radical process.