a) To a solution of ethyl 2-cyclohexanone carboxylate (18.9 mL, 118 mmol) in methanol (120 mL) was added ammonium carbamate (9.20 g, 118 mmol). The reaction mixture was stirred at room temperature for 1 hour until the ammonium carbamate was completely dissolved. After continuing to stir the reaction mixture for 1 h, the volatile solvent was removed by distillation under reduced pressure to afford ethyl 2-amino-1-cyclohexene-1-carboxylate as a white to pale yellow solid (19.9 g, quantitative yield). The product was characterized by 1H NMR (400 MHz, CDCl3): δ 1.28 (t, J = 7.2 Hz, 3H), 1.57-1.71 (m, 4H), 2.21 (t, J = 6.1 Hz, 2H), 2.26 (t, J = 6.1 Hz, 2H), 4.15 (q, J = 7.2 Hz, 2H), 6.06 (br s, 2H) .
