To a solution of (R)-tert-butyl 3-aminopiperidine-1-carboxylate (1.53 g, 7.6 mmol) in DMF (76 mL) was added Et3N (22 mmol) stirred for 15 min. 2-6-Dichloro pyrazine (1.14 g, 76 mmol) was added at RT and the reaction mixture was stirred at 100° C. overnight. The resulting reaction mixture was quenched with ice cold water and precipitate was formed. The precipitate was collected by filtration, washed with ice cold water and dried to obtain (R)-tert-butyl 3-(6-chloropyrazin-2-ylamino)piperidine-1-carboxylate (1.1 g, 43%). MS (ESI, pos. ion) m/z: 313 (M+1). To a solution of tributyltin hydride (1.39 g, 4.8 mmol) in THF (25 mL) at 0° C. was added LDA (1.8 M; 0.5 mL, 4.8 mmol) and stirred at the same temperature for 10 min. (R)-tert-butyl 3-(6-chloropyrazin-2-ylamino)piperidine-1-carboxylate (1.1 g) was added at 0° C. and the reaction mixture was stirred at RT for an additional 3 h. The resulting mixture was quenched with 10% KF aqueous solution and extracted with EtOAc. The organic layer was separated, dried over Na2SO4 and concentrated to dryness. The crude product was purified by column chromatography, using basic alumina, and eluting with 10% EtOAc/hexane to obtain pure (R)-tert-butyl 3-(6-(tributylstannyl)pyrazin-2-ylamino)piperidine-1-carboxylate (0.8 g, 48%). MS (ESI, pos. ion) m/z: 569.2 (M+1).
