General procedure for the synthesis of tert-butyl 1-tert-butoxycarbonyl-2,5-dihydro-1H-pyrrole-3-boronic acid pinacol ester from tert-butyl 3-(trifluoromethanesulfonyloxy)-2H-pyrrole-1(5H)-carboxylate and pinacol ester of bis(boronic acid): tert-butyl 3-(trifluoromethanesulfonyloxy)-2,5-dihydro-pyrrole-1-carboxylate (2.00 g, 6.3 mmol) was dissolved in 1,4 -dioxane (35 mL) and degassed potassium acetate (1.86 g, 18.9 mmol), Pd(dppf)Cl2-CH2Cl2 (154 mg, 0.19 mmol), dppf (105 mg, 0.19 mmol), and bis(pinacolato)ethylborane (1.92 g, 7.56 mmol) were added sequentially to this solution under nitrogen protection . The reaction mixture was stirred and reacted at 80 °C overnight. Upon completion of the reaction, the crude reaction mixture was concentrated and purified by fast column chromatography on silica gel (15-50% EtOAc/hexane gradient elution) to afford tert-butyl 5-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-2,5-dihydro-pyrrole-1-carboxylate as a white semi-solid (1.50 g, 81% yield).1H NMR (CDCl3, 300 MHz) δ 1.26 (s, 12H), 1.46 (s, 9H), 4.18 (m, 4H), 6.45 (bd, 1H, J = 14.10 Hz); MS (ESI) m/z = 240.2 (MH+ -t-Bu).
