1: cyanomethyl-phosphonic acid diethyl ester With sodium hydride in tetrahydrofuran; mineral oil T=0 - 20°C; 2: 3-oxo-azetidine-1-carboxylic acid tert-butyl ester in tetrahydrofuran; mineral oil Product distribution / selectivity;

1: diethyl cyanomethyl phosphate With potassium tert-butylate in tetrahydrofuran T=-14 - 5°C; 3 h; 2: 3-oxo-azetidine-1-carboxylic acid tert-butyl ester in tetrahydrofuran T=-10 - 20°C;

1.1: triethylamine; dimethyl sulfoxide; sulfur trioxide pyridine complex / dichloromethane / 3 h / 0 °C 2.1: sodium hydride / tetrahydrofuran; mineral oil / 1.58 h / 3 - 18.2 °C / Inert atmosphere 2.2: 24 h View Scheme