Synthesis of tert-butyl 3-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-1H-pyrazol-1-yl)azetidine-1-carboxylate (2-8): tert-butyl 3-(4-bromo-1H-pyrazol-1-yl)azetidine-1-carboxylate (2-8) was synthesized by dissolving compound 3-(4-bromo-1H-pyrazol-1-yl)tert-butyl azetidine-1-carboxylate (2-8) (225 mg, 0.74 mmol), biboronic acid pinacol ester (2-7) (227 mg, 0.89 mmol) and potassium acetate (247 mg, 2.52 mmol) were dissolved in 3 mL of dimethyl sulfoxide (DMSO) and the reaction mixture was purged with nitrogen for 15 min. Subsequently, dichlorobis(1,1'-bis(diphenylphosphino)ferrocene)palladium(II) (PdCl2(dppf)2-CH2Cl2) (30 mg, 2.52 mmol) was added. The resulting mixture was stirred at 80 °C overnight under nitrogen protection. After completion of the reaction, it was cooled to room temperature and the mixture was filtered through a diatomaceous earth pad and washed well with ethyl acetate. The filtrate was washed sequentially with water (2 x 50 mL) and brine (50 mL). The organic layer was dried with anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by silica gel column chromatography with the eluent being petroleum ether: ethyl acetate (3:2). The filtrate was concentrated under reduced pressure to give 250 mg of the target product 2-8 as a clear oil (97% yield).1H NMR (400 MHz, chloroform-d) δ ppm 1.18-1.27 (m, 9H), 1.28-1.34 (m, 6H), 1.41-1.49 (m, 6H), 4.22-4.33 (m, 2H), 4.36 (t, J = 8.59 Hz, 2H), 4.98-5.13 (m, 1H), 7.83 (s, 2H).
