To a stirred solution of compound 3 (0.800 g, 2.86 mmol, 1.00 equiv) in methanol (7.2 mL) was added zinc powder (0.930 g, 14.3 mmol, 5.00 equiv) followed by ammonium chloride solution (0.760 g, 14.3 mmol, 5.00 equiv) dropwise. After being stirred at RT for 5 h, DIPEA (0.460 g, 3.58 mmol, 1.25 equiv) and ethyl chloroformate (0.310 g, 2.87 mmol, 1.00 equiv) were added to reaction mixture at 10° C. and the stirring was continued for another 3 h at RT. After consumption of the starting material (by TLC), the reaction mixture was diluted with water (24 mL) and stirred for 1 h to give the solid. The obtained solid was filtered, dissolved in EtOAc (15 mL) and again filtered the un-dissolved solid. The filtrate was evaporated and recrystallized using n-hexane to afford compound 1A (0.250 g, 27.0%) as brown solid. TLC: 50% EtOAc/Hexane (Rf: 0.20) 1H NMR (500 MHz, CDCl3): δ 7.31 (t, J=7.5 Hz, 2H), 7.02 (t, J=6.8 Hz, 2H), 6.75 (d, J=6.8 Hz, 1H), 6.07 (t, J=6.8 Hz, 1H), 4.31 (s, 2H), 4.22-4.18 (m, 3H), 3.84 (br s, 2H, Exc), 1.29 (t, J=5.6 Hz, 3H); UPLC purity: 91.0%; LC-MS: m/z=322 (M+-1) at RT 3.37 (82.8%)
