[NH:1]([C:3]1[CH:8]=[N:7][CH:6]=[CH:5][N:4]=1)N.[Cl:9][C:10]1[CH:15]=[C:14]([C:16](=O)[CH2:17][C:18]2[CH:23]=[CH:22][C:21]([F:24])=[CH:20][CH:19]=2)[CH:13]=[CH:12][N:11]=1.O.C1(C)C=CC(S(O)(=O)=O)=CC=1.O>C1C=CC=CC=1>[Cl:9][C:10]1[CH:15]=[C:14]([C:16]2[NH:1][C:3]3=[N:4][CH:5]=[CH:6][N:7]=[C:8]3[C:17]=2[C:18]2[CH:19]=[CH:20][C:21]([F:24])=[CH:22][CH:23]=2)[CH:13]=[CH:12][N:11]=1Hydrazinopyrazine (6.2 g, 57 mmol) and 1-(2-chloropyridin-4-yl)-2-(4-fluorophenyl)ethanone (14 g, 57 mmol) were suspended in benzene (250 ml) and p-toluenesulfonic acid monohydrate (0.68 g) was added. The reaction mixture was then refluxed with azeotropic removal of water via Dean Stark trap. After 2 h, the benzene was removed in vacuo and di-ethylene glycol was added. The reaction mixture was heated at reflux. After 2 h, the reaction mixture was poured into ether with vigorous stirring. Water was added and the product was extracted into ether. The organic layer was dried over magnesium sulfate, filtered and concentrated in vacuo. Methanol was added and the solid was filtered off to give 6-(2-chloropyridin-4-yl)-7-(4-fluorophenyl)-5H-pyrrolo[2,3-b]pyrazine (4.9 g) as a solid.
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