163688-23-1

6127-17-9

Compound 5 (2.3 g, 8.12 mmol) was dissolved in dichloromethane (40 mL) under the protection of inert atmosphere and trifluoroacetic acid (7.5 mL) was slowly added under stirring at room temperature. The reaction mixture was stirred continuously at room temperature for 2 h. The reaction progress was monitored by thin layer chromatography (TLC). Upon completion of the reaction, the reaction was quenched with deionized water (40 mL) and subsequently extracted with dichloromethane (2 x 50 mL). The organic phases were combined, washed sequentially with saturated sodium bicarbonate solution (40 mL) and saturated saline (40 mL), dried over anhydrous sodium sulfate, filtered and concentrated under reduced pressure to give the crude product. The crude product was purified by recrystallization from 5% ethyl acetate/hexane mixed solvent to give compound 6 (1 g, 77% yield) as an off-white solid.1H NMR (500 MHz, DMSO-d6) δ: 11.02 (br s, 1H), 7.36 (d, J = 8.0 Hz, 1H), 7.25 (s, 1H), 6.90 (d, J = 8.5 Hz. 1H), 6.11 (s, 1H), 2.34 (s, 3H). Liquid chromatography-mass spectrometry (LC-MS) analysis showed a purity of 93.5% and a measured (M-H)- of 164 (column: XBridge C-18, 50×3.0 mm, 3.5 μm; mobile phase: 5 mM ammonium acetate/acetonitrile; flow rate: 0.8 mL/min).