A cyclic diamine, 1-methyl-4-(trifluoromethylthio)piperazine (MTTP, 1), prepared by a one-step reaction from commercial materials, is a shelf-stable and powerful electrophilic trifluoromethylthiolating (CF3S) reagent with wide reactivity profile. Activation of 1 with triflic acid (TfOH) yields two reactive species A and B, depending on the molar ratios of TfOH/1. B showed unprecedented high reactivity, making possible the trifluoromethylthiolation of electron-deficient aromatic systems. In addition, B accomplished the trifluoromethylthiolation of active methylene compounds under acidic conditions.