27.2 g of 4-[(diethoxyphosphoryl)methyl]benzoic acid was suspended in a mixture of 60 ml of dichloromethane and 2 ml of DMF. 13.1 g of thionyl chloride was added, and the resulting mixture was refluxed for 1 hour. After completion of reaction, the reaction mixture was allowed to cool and then slowly added dropwise, with ice-cooling and stirring, to a solution of 18.5 g of 2-(N-methylcarbamoyl)-5-chloroaniline in a mixture of 50 ml of pyridine and 30 ml of dichloromethane. After completion of addition, the resulting mixture was stirred at room temperature for 48 hours. Then, 50 ml of water was added to the reaction mixture to precipitate crystals. The crystals were then collected by filtration, fully washed with water and dried, giving 23.6 g of diethyl 4-{[5-chloro-2-(N-methylcarbamoyl)phenyl]carbamoyl}benzylphosphonate.
