C[O:2][C:3](=[O:15])[C:4]1[CH:9]=[C:8]([O:10][CH2:11][CH3:12])[C:7]([Cl:13])=[C:6]([NH2:14])[CH:5]=1.[CH:16]([S:18]([CH:21]=[CH2:22])(=[O:20])=[O:19])=[CH2:17].O>P(=O)(O)(O)O>[Cl:13][C:7]1[C:8]([O:10][CH2:11][CH3:12])=[CH:9][C:4]([C:3]([OH:2])=[O:15])=[CH:5][C:6]=1[N:14]1[CH2:22][CH2:21][S:18](=[O:20])(=[O:19])[CH2:16][CH2:17]1A mixture of 3-amino-4-chloro-5-ethoxy-benzoic acid methyl ester (1.0 g, 4.35 mmol, 1.0 equiv) and divinylsulfone (0.44 mL, 0.51 g, 4.35 mmol, 1.0 equiv) in phosphoric acid 85% (25 mL) was heated to 140° C. overnight. The reaction mixture was poured into water (50 mL) and extracted with dichloromethane (3×50 mL). The combined organic phases were dried over MgSO4, the solvent removed by evaporation under reduced pressure and the crude material purified with column chromatography on silica eluting with heptane/ethyl acetate (1:1+1% acetic acid) yielding 0.18 g (12%) of the title compound. 1H NMR (300 MHz, CDCl3): δ 1.51 (t, J=7.0 Hz, 3H), 3.25-3.29 (m, 4H), 3.57-3.60 (m, 4H), 4.19 (q, J=7.0 Hz, 2H), 7.44 (d, J=1.7 Hz, 1H), 7.47 (d, J=1.7 Hz, 1H). MS (ISN): 332.1 [M−H]−.
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