To a solution of dimethylamine hydrochloride (49.66 mg, 0.61 mmol) in dichloromethane (50 mL) was added and triethylamine (102 mg, 1.01 mmol) and stirred for 10 min. Then methyl 3-[6-(chlorosulfonyl)-1,2,3,4-tetrahydroquinolin-1-yl]-2-(4-fluorophenyl)quinoxaline-6-carboxylate (260 mg, 0.51 mmol) in dichloromethane (20 mL) was added dropwise with stirring for 30 min at room temperature. The reaction mixture was concentrated under vacuum to give the residue, which was applied onto a silica gel column with 2%-5% ethyl acetate in petroleum ether to afford methyl 3-[6-(dimethylsulfamoyl)-1,2,3,4-tetrahydroquinolin-1-yl]-2-(4-fluorophenyl)quinoxaline-6-carboxylate as a yellow solid (240 mg, 91%).
