A solution of 3-(2-nitro-3-piperidin-1-yl-phenyl)-2-oxo-propionic acid ethyl ester (ii) in THF is treated with potassium ethoxide (“KOEt”) (1 eq), followed by bromoethyl pyruvate (1.05 eq), at 0° C. The reaction is allowed to warm to room temperature over 90 min. The reaction is diluted with water and ether, partitioned, and the aqueous layer is washed with ether. The combined organic layers are dried over MgSO4, filtered and concentrated. Chromatography gives 3-(2-nitro-3-piperidin-1-yl-phenyl)-2,5-dioxo-hexanedioic acid di ethyl ester (iii).
