Abstract A general and efficient room-temperature procedure is developed for high-yield synthesis of 2H-benzo[b][1,4]thiazin-3(4H)-onederivatives in one pot from the reaction of 2-aminothiophenols with 2-bromoalkanoates in ionicliquid [bmim]NO3 without the use of any catalyst, base, or additive. Products were obtained in good yields by simple extraction with Et2O followed by evaporation of the volatile