Step 5: Synthesis of tert-butyl 5-methyl-(pyrrolidin-3-one)-1-carboxylate
1-Benzyl-5-methylpyrrolidin-3-one (2 g, 10.57 mmol) and di-tert-butyl dicarbonate (Boc2O, 2.77 g, 12.98 mmol) were dissolved in ethanol (EtOH, 20 mL) and palladium/carbon (Pd/C, 0.3 g) was added as a catalyst. The reaction mixture was stirred overnight under hydrogen (H2, 40 psi) atmosphere. The progress of the reaction was monitored by thin layer chromatography (TLC) and after confirming the completion of the reaction, the catalyst was removed by filtration and the filtrate was concentrated. The residue was purified by column chromatography (eluent ratio petroleum ether/ethyl acetate = 9:1) to afford tert-butyl 5-methyl-(pyrrolidin-3-one)-1-carboxylate (1.4 g, 66.5% yield) as a colorless oil.
Product characterization data: 1H NMR (400 MHz, CDCl3) δ ppm 7.33-7.23 (m, 5H), 4.18-4.15 (d, J=13.2 Hz, 1H), 3.29-3.14 (m, 1H), 2.99-2.93 (m, 1H), 2.65-2.60 (m, 1H), 2.51-2.45 (m , 1H), 2.16-2.08 (m, 1H), 1.34-1.32 (m, 3H); no ionization signal was detected by ES-LCMS.
