1: diethoxyphosphoryl-acetic acid ethyl ester With sodium hydride in tetrahydrofuran T=20°C; 0.5 h; 2: 1,1,5,5-tetraethyl-1,5-diaza-3-fluoro-2,4-pentadienium iodide in tetrahydrofuran T=20°C; 3 h; Further stages.;