Step 1. 4-Piperidone monohydrate hydrochloride (5 g, 0.033 mol) was mixed with tert-butyl bromoacetate (6.98 g, 0.037 mol) and potassium carbonate (13.65 g, 0.099 mol) in dimethylformamide (100 ml) and reacted for 24 hours at 100 °C. After completion of the reaction, the mixture was cooled and concentrated in vacuum. The residue was partitioned between saturated potassium carbonate solution and ether (2 x 50 ml). The organic layers were combined, dried over anhydrous sodium sulfate, filtered and evaporated to dryness to give 7.36 g of tert-butyl 2-(4-oxopiperidin-1-yl)acetate in 94% yield. The product was characterized by 1H NMR (CDCl3): δ 1.45 (9H, s), 2.45 (4H, t, J=7Hz), 2.3-2.4 (4H, m), 3.29 (2H, s).
