General procedure for the synthesis of tert-butyl 4-aminothiocarbonyltetrahydropyridine-1(2H)-carboxylate from tert-butyl 4-carbamoylpiperidine-1-carboxylate: tert-butyl 4-carbamoylpiperidine-1-carboxylate (2.65 g, 11.62 mmol) was dissolved in a solvent mixture of DME/DCM (2:1, 78 mL), followed by addition of Lawesson reagent (2.35 g, 5.81 mmol, 0.5 equiv). The reaction mixture was stirred at room temperature overnight. After completion of the reaction, the solvent was removed under reduced pressure and the residue was dissolved in ethyl acetate and washed with saturated aqueous K2CO3 solution. The organic layer was separated, dried with anhydrous Na2SO4, filtered and concentrated to dryness. The obtained residue was ground with ether and dried to give tert-butyl 4-aminothiocarbonyltetrahydropyridine-1(2H)-carboxylate (2.65 g, 92% yield) as a white solid. The product was analyzed by HPLC showing a retention time (Rt) of 5.06 min. 1H NMR (401 MHz, DMSO-d6) δ ppm: 9.39 (br.s., 1H), 9.09 (br.s., 1H), 4.00 (d, J=12.6 Hz, 2H), 2.77-2.61 (m, 3H), 1.71-1.51 (m , 4H), 1.39 (br.s., 9H).
