To a solution of (E)-ethyl 2-(4-(2-(3-(diethoxyphosphoryl)-3,3-difluoropropoxy)ethoxy)-2-methoxybenzylidene)-3-oxobutanoate (1 equiv.) in MeOH (0.20 M) was added guanidine carbonate (1.1 equiv.) and the reaction mixture was heated to 80° C. for 3 h. At this point the reaction mixture was allowed to cool to room temperature and it was then diluted with water and EtOAc. The resulting mixture was transferred to a separatory funnel and washed with EtOAc three times. The combined organic layers were dried over anhydrous Na2SO4 and the volatiles were removed in vacuo. The resulting residue was purified by a COMBIFLASH™ system using a gradient of 0-10% MeOH/DCM to provide the title compound (15%) as a solid.
