Methyl chloroformate → Methyl (3S)-3-(hydroxymethyl)piperazine-1-carboxylate

A solution of the product of stage (ii) (0.080 g) in dry acetonitrile (10 ml) was treated with a solution of methyl chloroformate (71 mg; 0.75 mmol) in dry acetonitrile (3 ml) over a 5 min period. The mixture was stirred at ambient temperature for 30 min and aqueous sodium carbonate solution (1 ml) was added. The solvent was removed in vacuo and the aqueous residue was extracted with dichloromethane (3×25 ml) and chloroform (3×25 ml). The extract was washed with aqueous sodium carbonate solution (5 ml: 1M), and the combined extracts were dried and evaporated in vacuo to give the title compound as an oil (0.1 g).