A solution of compound 3 (10.85 g; 29 mmol) in dry THF (100 mL) kept in an ice bath was treated with a solution of 1M lithium hydroxide (100 mL) and stirred for 4 h at 0° C. until the starting material disappeared (as shown by TLC). The solvent was removed and the residue was diluted with water (25 mL). The pH of the aqueous solution was adjusted to ˜2 with 5% HCl and the solution was extracted with ethyl acetate (2×250 mL) and washed with brine (100 mL). The organic extract was dried over anhydrous sodium sulfate, filtered and concentrated, yielding a crude product which was purified by flash chromatography (silica gel; hexane/ethyl acetate 50:50) to give 4 as a white solid (8.8 g; 84% yield). 1H NMR (DMSO-d6) δ 8.1 (s, 1H), 7.5 (s, 1H), 7.3 (m, 5H), 5.0 (s, 2H), 4.4 (m, 1H), 4.2 (m, 1H), 2.8 (s, 1H), 2.5 (m, 1H), 2.4 (m, 1H), 1.6 (m, 2H), 1.4 (m, 1H), 0.8 (d, 6H)
