General procedure for the synthesis of N-(3,4-dichlorobenzyl)-N-methylamine from 3,4-dichlorobenzaldehyde and methylamine: 3,4-dichlorobenzaldehyde (600 mg, 3.43 mmol, 1.0 eq.) was mixed with methylamine (0.64 mL, 5.14 mmol, 8.03 M in ethanol, 1.5 eq.) in anhydrous 1,2-dichloroethane (12 mL) and stirred under nitrogen protection for 3 hours. Subsequently, sodium triacetoxyborohydride (1.02 g, 4.81 mmol, 1.4 eq.) was added and the reaction mixture continued to be stirred at room temperature for 18 hours. Upon completion of the reaction, the mixture was poured into 2 M aqueous sodium carbonate solution and extracted with ethyl acetate (3 x 10 mL). The organic phases were combined, dried with anhydrous magnesium sulfate and concentrated under reduced pressure. Finally, the product was purified by silica gel column chromatography with the eluent methanol:methanol:dichloromethane containing 7N ammonia (the ratio was gradually changed from 1:5:94 to 1:10:89 and finally 1:15:84) to give a light yellow oily product (455 mg, 70% yield).
