Under inert gas, 7.00 g of C-(3-bromophenyl)-N-(2,4-dimethoxybenzyl)methanesulfonamide were initially charged in 120 ml of THF, and then, at a temperature of −78° C., 25.14 ml of a 1.6 N methyllithium solution in diethyl ether were added dropwise and the mixture was stirred at constant temperature for 10 minutes. Subsequently, 7 ml of acetone were added. After stirring for 5 minutes, the reaction solution was admixed with 5 ml of acetic acid and stirred for a further 5 minutes, and 100 ml of ethyl acetate were added to the mixture, which was washed with 1×100 ml and 1×50 ml of a saturated aqueous sodium hydrogencarbonate solution and 2×50 ml of a saturated aqueous sodium chloride solution. The organic phase was dried over MgSO4 and concentrated by rotary evaporation. The residue (8.63 g) was used in the next reaction without further purification.
