General procedure for the synthesis of 1-Boc-5-ethyl-2,4-dioxopiperidine from tert-butyl 2,4-dioxopiperidine-1-carboxylate and ethyl iodide: tert-butyl-2,4-dioxopiperidine-1-carboxylate (1.92 g, 9.0 mmol) was dissolved in anhydrous tetrahydrofuran (THF, 65 mL) under nitrogen protection, and cooled to -20°C. The reaction was carried out under nitrogen protection. Lithium bis(trimethylmethylsilyl)amide (LiHMDS, 1 M THF solution, 27 mL) was added slowly and dropwise. After stirring the reaction mixture for 20 minutes, ethyl iodide (2.53 mL, 4.9 g, 31.3 mmol) was added and stirring was continued at -20 °C for 2 hours. After completion of the reaction, the mixture was poured into 5% aqueous potassium bisulfate (KHSO4) and extracted with dichloromethane (DCM, 2×). The organic layers were combined, washed with water, dried over anhydrous sodium sulfate (Na2SO4) and concentrated under reduced pressure. The residue was purified by column chromatography (hexane/ethyl acetate, 1:1) to give 1.4 g of the target product (5.8 mmol, 64% yield). Electrospray ionization mass spectrometry (ESI-MS) showed m/z 242 ([M+H]+).
