Ethyl formate → Benzyl 2-chloro-3-oxopropanoate

To potassium tert-butoxide (141 mL, 141 mmol) at 0° C. was added dropwise a solution of benzyl 2-chloroacetate (26.8 g, 141 mmol) and ethyl formate (11.6 mL, 141 mmol) in Et2O (45 mL). The reaction was warmed to ambient temperature and stirred for 16 hours. The reaction mixture was filtered and washed with cold ether (100 mL). The potassium salt was dissolved in H2O (50 mL) and the solution was acidified with concentrated HCl to pH=4 in a cold bath. The solution was extracted with ether and the organic phase was dried (MgSO4) and concentrated to give the crude product. A lower boiling point impurity was removed by vacuum distillation (90° C., 5 mm Hg) and the residue was taken directly to the next step.