The general procedure for the synthesis of tert-butyl 4-(((trifluoromethyl)sulfonyl)oxy)-5,6-dihydropyridine-1(2H)-carboxylate from N-phenylbis(trifluoromethylsulfonyl)imide was as follows: diisopropylamine (22 ml) was dissolved in anhydrous THF (125 ml) and the solution was cooled down to -78 °C. Slowly add n-butyllithium (62.5 ml, 2.5 M hexane solution). After stirring for 15 min, a solution of tert-butyl 4-oxopiperidine-1-carboxylate (28.32 g) in THF (100 ml) was added dropwise. The reaction mixture was continued to be stirred at -78 °C for 1 h followed by dropwise addition of THF (150 ml) solution of N-phenyl trifluoromethanesulfonimide (53.8 g). The reaction mixture was stirred at -78 °C for 2 h. The mixture was slowly warmed to room temperature and stirred overnight. After completion of the reaction, the mixture was concentrated in vacuum and the residue was dissolved in ether (1000 ml). The organic layer was washed sequentially with water (500 ml), 2M sodium hydroxide solution (3 x 500 ml), water (500 ml) and brine (500 ml), then dried with magnesium sulfate, and concentrated to give tert-butyl 4-(((trifluoromethyl)sulfonyl)oxy)-5,6-dihydropyridine-1(2H)-carboxylate as a light brown oil (45.38 g, 96% yield). It could be used in the subsequent reaction without further purification. The product was confirmed by 1H NMR (CDCl3): δ1.48 (9H, s), 2.44 (2H, m), 3.63 (2H, t), 4.00 (2H, q), 5.70 (1H, br).
