To a solution of compound 3f (6.6 g, 20 mmol) in dry THF (100 mL) was added NaH (60%, 960 mg, 24 mmol) in small portions at 0° C. and stirred for 1 hr. Then compound 3b (5 g, 22 mmol) in THF (50 mL) was added dropwise, and the reaction mixture was allowed to stir at rt overnight. The reaction was quenched with water and extracted with EA (2×100 mL). The combined organic extracts were dried over anhydrous Na2SO4 and concentrated under reduced pressure. The residue was purified by CC eluting with PE:EA=9:1 to give 3g as a white solid (3.2 g, 34% yield).
