[CH3:1][N:2]1[CH:6]=[C:5]([C:7]([F:10])([F:9])[F:8])[C:4]([C:11](O)=O)=[CH:3]1.ClS([N:18]=C=O)(=O)=O.CN(C)C=O.O>C(#N)C.C(OCC)(=O)C>[CH3:1][N:2]1[CH:6]=[C:5]([C:7]([F:10])([F:9])[F:8])[C:4]([C:11]#[N:18])=[CH:3]1A mixture of 1-methyl-4-(trifluoromethyl)pyrrole-3-carboxylic acid (1.93 g, 0.01 mol) in acetonitrile at 40°-45° C. is treated dropwise with chlorosulfonylisocyanate (1.41 g, 0.01 mol), heated at 40° C. for 24 hours, cooled to room temperature, treated with dimethylformamide (1.46 g, 0.02 mol), heated at 40° C. for 8 hours, cooled to room temperature, stirred for 48 hours at room temperature and poured into water. The resultant mixture is extracted with ethyl acetate. The extracts are combined, washed sequentially with water and brine, dried (MgSO4) and concentrated in vacuo to afford an oily solid residue. The residue is taken up in ethyl acetate, washed with 1% aqueous sodium hydroxide, dried (MgSO4) and concentrated in vacuo to give a yellow oil residue. Kugelrohr distillation at 100°-110° C./2 mm Hg yields the title product as a white solid, 0.95 g (54%).
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