Step 4: Preparation of tert-butyl {3-[4-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]oxetan-3-yl}carbamate. Tert-butyl (3-(4-bromophenyl)oxetan-3-yl)carbamate (193 mg), pinacol ester of bis(boronic acid) (179 mg), and potassium acetate (173 mg) were dissolved in dimethyl sulfoxide (3 mL), PdCl2(dppf)CH2Cl2 (14 mg) was added, and degassed for 5 min. Subsequently, the reaction mixture was stirred at 80 °C for 5 hours. After completion of the reaction, the reaction mixture was diluted with ethyl acetate and filtered. The filtrate was washed with brine (5 times) and the organic phase was dried with anhydrous sodium sulfate and concentrated under reduced pressure. Purification by column chromatography (eluent: 0-20% hexane solution of ethyl acetate) afforded the target product (189 mg, 86% yield).1H NMR (CDCl3, 400 MHz) δ: 7.85 (d, J = 8.3 Hz, 2H), 7.55 (d, J = 8.3 Hz, 2H), 5.29 (br s, 1H), 5.08-4.74 (m, 4H), 1.49-1.18 (m, 9H), 1.35 (s, 12H).LCMS: 376 [M + H].
