A mixture of 7-nitro-3,4-dihydro-2H-benzo[b][1,4]thiazine (1 g, 5.10 mmol), 1-(2-chloroethyl)piperidine hydrochloride (1.876 g, 10.19 mmol), and tetrabutylammonium bromide (0.082 g, 0.255 mmol) in dichloromethane (10 mL) and 50% NaOH solution (10 mL) was stirred at room temperature overnight (16 hours). The mixture was diluted with dichloromethane (5 mL) and water (20 mL), and the mixture was then transferred to a separatory funnel. The organic layer was removed, and the aqueous layer was extracted in dichloromethane (2×10 mL). The combined organic layers were dried (Na2SO4), filtered, and concentrated. The red crude material was subjected to column chromatography on silica gel using the Biotage purification system (80 g silicycle column; solvent gradient: dichloromethane 3CV, ramp to 6:94 (2M NH3 in methanol):CH2Cl2 over 15CV; 254 nm monitoring wavelength; flow=45 mL/minute), to give an orange solid (0.937 g, 59.8%). 1H-NMR (DMSO-d6) δ 7.85-7.81 (m, 2H), 6.82 (d, J=9.0 Hz, 1H), 3.82-3.79 (m, 2H), 3.58 (t, J=6.9 Hz, 2H), 3.08-3.04 (m, 2H), 2.50-2.45 (m, 2H), 2.44-2.34 (m, 4H), 1.49-1.46 (m, 4H), 1.40-1.37 (m, 2H); ESI-MS (m/z, %): 308 (MH+, 100).
