General procedure for the synthesis of (2-aminopyridin-4-yl)boronic acid from 2-amino-4-chloropyridine: 2-amino-4-chloropyridine (3 g, 23.34 mmol), bis(pinacolato)diboron (17.78 g, 70.1 mmol), 2-dicyclohexylphosphino-2',6'-dimethoxybiphenyl (0.38 g, 0.93 mmol), tris( dibenzylideneacetone) dipalladium(0) (0.21 g, 0.23 mmol) and potassium acetate (3.89 g, 39.67 mmol) were mixed in 1,4-dioxane (78 mL) under nitrogen atmosphere. The reaction mixture was stirred at 100 °C for 3 hours. Upon completion of the reaction, the hot reaction mixture was filtered through diatomaceous earth and washed with ethyl acetate (EtOAc). The organic layer was concentrated under vacuum and the residue was precipitated with diisopropyl ether (DIPE) to afford the intermediate compound 1-24 ((2-aminopyridin-4-yl)boronic acid) as a white solid (5.84 g, quantitative yield), which could be used in the next reaction without further purification.
