[C:1]1([CH3:20])[CH:6]=[CH:5][C:4]([S:7]([N:10]2[CH:14]=[CH:13][C:12](/[CH:15]=[CH:16]/[C:17](O)=[O:18])=[CH:11]2)(=[O:9])=[O:8])=[CH:3][CH:2]=1.C(Cl)(=O)C(Cl)=O.C[Si](C)(C)[O:29][NH2:30].Cl>ClCCl.CN(C)C=O>[OH:29][NH:30][C:17](=[O:18])/[CH:16]=[CH:15]/[C:12]1[CH:13]=[CH:14][N:10]([S:7]([C:4]2[CH:5]=[CH:6][C:1]([CH3:20])=[CH:2][CH:3]=2)(=[O:9])=[O:8])[CH:11]=1
0.231 g of (E)-3-[1-(toluene-4-sulfonyl)-1H-pyrrol-3-yl]-acrylic acid (compound A1) are dissolved in 8 ml of dichloromethane at room temperature. Then 50 μl of N,N-dimethylformamide (DMF) are added, 0.275 g of oxalic acid chloride dissolved in 2 ml of dichloromethane are added dropwise and stirred for 1.5 hour. To the solution are added 0.439 g of O-(trimethylsilyl)hydroxylamine and stirred for 15 minutes. Then 20 ml of aqueous hydrochloric acid (1 M strength) are added and extracted with ethyl acetate. The combined organic phase is dried over sodium sulfate. Afterwards it is filtered and evaporated under vacuo. The crude product is purified by silica gel flash chromatography using a gradient of dichloromethane and methanol from 98:2 to 6:4 to yield 0.050 g of the title compound as a white solid.
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