Diethyl (cyanomethyl)phosphonate → Tert-butyl 3-(3-cyanoallyl)azetidine-1-carboxylate

To a solution of potassium tert-butoxide, 1M in tetrahydrofuran (3694 μl, 3.69 mmol) at 0° C. was added dropwise by syringe a solution of diethyl cyanomethylphosphonate (570 μl, 3.52 mmol) in 5 ml tetrahydrofuran. The reaction mixture was warmed to room temperature and then cooled to 0° C. again. This solution was treated with tert-butyl 3-(2-oxoethyl)azetidine-1-carboxylate (701 mg, 3.52 mmol) in 2 ml tetrahydrofuran dropwise by syringe and then allowed to warm to room temperature. After stirring overnight the gelatinous mixture was quenched with water (20 ml) and extracted with ethyl acetate (2×20 ml); the organic layers were washed with brine (20 ml), dried with magnesium sulfate, filtered and concentrated. The liquid residue was flash chromatographed to give the title compound as a 1:1 mixture of E/Z isomers.