To a mixture of 4-(5-bromo-3-methylpyridin-2-yl)piperazine-1-carboxylic acid tert-butyl ester (3.6 g), bis(tricyclohexylphosphine)palladium(II)dichloride (396 mg), tripotassium phosphate (12 g) and cyclopropylboronic acid (2.1 g) were added toluene (30 mL) and water (1.5 mL), and the mixture was stirred with heating under reflux for 8 hr. The reaction mixture was cooled, water was added, and the mixture was extracted with ethyl acetate. The organic layer was washed with saturated brine, and the solvent was evaporated. The obtained residue was purified by column chromatography (chloroform) to give 4-(5-cyclopropyl-3-methylpyridin-2-yl)piperazine-1-carboxylic acid tert-butyl ester (2.2 g). The obtained 4-(5-cyclopropyl-3-methylpyridin-2-yl)piperazine-1-carboxylic acid tert-butyl ester (2.2 g) was dissolved in chloroform (5 mL), 4N hydrogen chloride/ethyl acetate (5 mL) was added, and the mixture was stirred at room temperature overnight. To the reaction mixture was added ethyl acetate (20 mL), and the precipitate was collected by filtration to give the title compound (1.3 g).
