The general procedure for the synthesis of tert-butyl 1-N-tert-butoxycarbonyl-4-(bromomethylene)piperidine from 4-(dibromomethylene)piperidine-1-carboxylate was carried out as follows: tert-butyl 4-(dibromomethylene)piperidine-1-carboxylate (12 g, 33.8 mmol) was dissolved in methanol (80 ml) under nitrogen protection and cooled to 0°C. Subsequently, tetrahydrofuran (40 ml) and ammonium chloride (14.46 g, 270 mmol) were added. The reaction mixture was stirred at 0°C for 30 min and then zinc powder (8.85 g, 135 mmol) was added. The reaction mixture was gradually warmed to room temperature and stirring was continued for 4 hours. After completion of the reaction, the mixture was filtered and the solid was washed with methanol. The filtrate was concentrated under reduced pressure to give a white solid. The solid was dissolved in a mixture of ethyl acetate and water to separate the organic and aqueous layers. The organic layer was dried with magnesium sulfate and concentrated under reduced pressure to give tert-butyl 4-(bromomethylene)piperidine-1-carboxylate (9 g, 96% yield). The product was confirmed by 1H NMR (400 MHz, DMSO-d6): δ 6.26 (s, 1H), 3.19-3.43 (m, 4H), 2.15-2.35 (m, 4H), 1.41 (s, 9H). The mass spectrum (ES+) showed molecular ion peaks of 220 and 222.
