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Compound 208 (350 mg, 1.09 mmol) was stirred with a 1:1 mixture of acetic acid glacial and conc. HCl in a 100° C. oil bath for 2.5 h. Ethyl acetate (100 mL) and ice water (30 mL) were added. The ethyl acetate layer was separated, washed with ice water, dried over Na2SO4 and concentrated. The resulting syrup was crystallized with ether to afford compound 211 as red crystals (253 mg, 79%); mp 157° C.; 1H NMR (DMSO-d6) δ 8.04-7.96 (m, 1H), 7.91-7.74 (m, 3H), 5.43 (dd, J=5.1 Hz, J=9.6 Hz, 1H), 2.42-2.33 (m, 2H), 2.30-2.26 (m, 2H); MS (DEI) m/z 293 (M); HRMS (DEI) calcd. for C13H11NO5S 293.0358 (M+). found 293.0363; Anal. (C13H11NO5S) H, N; C: calcd, 53.24. found, 53.88.

1. customThe ethyl acetate layer was separated
2. washwashed with ice water
3. dry with materialdried over Na2SO4
4. concentrationconcentrated
5. customThe resulting syrup was crystallized with ether