Ethyl bromoacetate → Tert-butyl 2-(2-ethoxy-2-oxoethyl)hydrazine-1-carboxylate

Triethylamine (13.94 ml., 0.1 mol.) was added to a solution of hydrazine carboxylic acid, 1,1-dimethylethyl ester (13.216 g., 0.1 mole) in benzene (100 ml.), followed by the addition of ethyl bromoacetate (11.09 ml., 0.1 mol.). The reaction mixture was refluxed (oil bath, 95°-100° C.) for 14 hours, after which triethylamine (1.4 ml., 0.01 mol.) was added followed by ethyl bromoacetate (1.1 ml., 0.01 mole). After refluxing for an additional 8 hours, triethylamine (2 ml., 0.015 mol.) and ethyl bromoacetate (1.4 ml., 0.013 mole) were added. The mixture was allowed to reflux for another 14 hours (total 36 hours). After cooling to room temperature, the reaction mixture was filtered and the solid triethylamine, hydrochloride salt was washed with ethyl acetate/hexane (1:1). The combined filtrate was diluted with ethyl acetate, washed with saturated sodium bicarbonate, water, brine, dried (sodium sulfate) and filtered. The filtrate was concentrated in vacuo to afford 19.38 g. of crude product as a yellow syrup which was used for the next reaction without purification.