O.[NH2:2]N.[Cl:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][C:6]=1[C:11](=O)[CH:12]=[CH:13][N:14](C)C>C(O)C>[Cl:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][C:6]=1[C:11]1[CH:12]=[CH:13][NH:14][N:2]=17 g (0.0540 mol) of hydrazine hydrate are added, slowly and at room temperature, to a solution of 10.5 g (0.050 mol) of 1-(2-chlorophenyl)-3-dimethylamino-2-propen-1-one, prepared in Example 1, in 60 ml of ethanol. The reaction mixture is stirred for 5 hours at room temperature then left standing for 12 hours before being concentrated to dryness. The residue is recrystallised from a heptane/ethyl acetate mixture. 6.9 g (0.0386 mol) of 3-(2'-chlorophenyl)-1H-pyrazole are obtained, which melts at 93° C. (yield 77%) (compound 60).
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