1: diiodomethane With diethylzinc; trifluoroacetic acid in hexane; dichloromethane T=-5 - 0°C; 0.833333 h; 2: 2,2-difluoro-4-pentenoic acid ethyl ester in hexane; dichloromethane 16.42 h; CoolingReflux; Product distribution / selectivity;