The general procedure for the synthesis of ethyl (1R,2R)-2-(3,4-difluorophenyl)cyclopropanecarboxylate from triethyl phosphonoacetate and (S)-2-(3,4-difluorophenyl)oxirane was as follows: sodium tert-butoxide (115.2 g, 1.2 mol) and triethyl phosphonoacetate (269.0 g, 1.2 mol) with toluene (150 g) were added to a 2 L three-necked flask and heated to 100 °C. Subsequently, a toluene solution of (S)-2-(3,4-difluorophenyl)oxirane was slowly added dropwise, and the reaction temperature was controlled to be maintained at 100 °C, and the reaction lasted for 4 hours. After completion of the reaction, the reaction mixture was cooled and quenched by addition of water (500 g). The organic phase was separated, dried with anhydrous sodium sulfate and concentrated to afford the target product ethyl (1R,2R)-2-(3,4-difluorophenyl)cyclopropanecarboxylate 203.9 g in 90.6% yield, 99.2% ee value and 99.2% purity.
