General procedure for the synthesis of 4-Boc-1-(5-bromo-2-pyridinyl)piperazine from 2,5-dibromopyridine and N-BOC-piperazine: 2,5-dibromopyridine (2 g, 10.7 mmol), sodium tert-butoxide (1.6 g, 16.6 mmol), xantphos (400 mg, 0.7 mmol) and toluene (100 mL) and purged with argon for 5 min. Subsequently, tert-butyl piperazine-1-carboxylate (3.4 g, 14.30 mmol) and Pd2(dba)3 (200 mg, 0.21 mmol) were added to the reaction system, and the reaction was heated at 80 °C for 4 h (TLC monitoring showed complete consumption of raw materials). Upon completion of the reaction, the reaction mixture was diluted with EtOAc (200 mL), water (100 mL) was added, filtered through a bed of diatomaceous earth, and the filter bed was washed with EtOAc (2 x 30 mL). The organic phases were combined, washed with brine (50 mL), dried over anhydrous Na2SO4 and concentrated under reduced pressure to give the crude product. The crude product was purified by silica gel column chromatography (100-200 mesh, 50 g, 10-20% EtOAc-hexane gradient elution) to give tert-butyl 4-(5-bromo-2-pyridinyl)piperazine-1-carboxylate (3 g, 82%) as a yellow solid.LCMS (ESI+): m/z: 342.57 [M+H]+.
