To a anhydrous THF (22 mL) solution of the carboxylic acid 55 (2.97 g, 4.28 mmol) was added 1,1′-carbonyl diimidazole (800 mg, 4.93 mmol) at room temperature. In separate flask, nitromethane (0.92 mL, 17.12 mmol) was added to a THF (9 mL) solution of NaH (200 mg, 4.93 mmol). The resulting white suspension was stirred at room temperature for 3 h. Then the prepared acyl imidazole solution was added to the suspension through a cannula at room temperature. After the transfer, the mixture was heated to 50° C. for 1.5 h. It was cooled to room temperature and quenched with 1.0 M HCl. The organic layer was extracted with ethyl acetate, dried over anhydrous MgSO4, filtered and concentrated in vacuo. The residue was purified by silica column chromatography to provide the titled compound (3.13 g, 99%).
