trifluoroacetic acid 2.5 h; Ambient temperature;

Multi-step reaction with 4 steps 1: 68 percent / diethyl cyanophosphonate, Et3N / dimethylformamide / 0.5 h / 0 °C2: 86 percent / (COCl)2, (CH3)2SO / CH2Cl2 / 0.33 h / -78 °C3: 69 percent / lithium bis(trimethylsilyl)amide / tetrahydrofuran / 2.5 h / 0 °C4: 100 percent / 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), H2O / CH2Cl2 / 0.5 h / Ambient temperature  

Multi-step reaction with 2 steps 1: 69 percent / lithium bis(trimethylsilyl)amide / tetrahydrofuran / 2.5 h / 0 °C2: 100 percent / 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), H2O / CH2Cl2 / 0.5 h / Ambient temperature