A 100-mL single-neck round-bottomed flask equipped with a magnetic stirrer and a reflux condenser was charged with 1,4-dioxane (40 mL), (S)-tert-butyl 4-(6-amino pyridin-3-yl)-3-methylpiperazine-1-carboxylate 105b (2.04 g, 7.0 mmol), 3-bromo-5-chloro-2-methoxypyridine (2.8 g, 12.6 mmol), Pd2(dba)3 (640 mg, 0.70 mmol), XantPhos (404.6 mg, 0.70 mmol), and cesium carbonate (4.56 g, 14.0 mmol). After three cycles of vacuum/argon flush, the mixture was heated at 100° C. for 4 h. After this time the reaction was cooled to room temperature. It was then filtered and the filtrate was evaporated under reduced pressure. The residue was purified by silica-gel column chromatography eluting with 1:3 ethyl acetate/petroleum ether to afford 138a (1.7 g, 57%) as a yellow solid. MS-ESI: [M+H]+ 434.2
