Pyrazole condensation with carbonyl groups

The formation of 4-cyano p3rrazole derivatives 3 can be rationalized as the acid protonated nitrogen of dimethylamino group and was replaced by hydrazine and then NH2 of the hydrazine condenses with carbonyl carbon to form pyrazole ring. When the condensation of 3-dimethylarnino-2-bezoyl-propenenitrile la and N-methyl ester of hydrazine was carried out, the ester group has been hydrolyzed and decarboxylated to give IH-pyrazole derivative 3f. 

Scheme 4 shows in a general manner cyclocondensations considered to involve reaction mechanisms in which nucleophilic heteroatoms condense with electrophilic carbonyl groups in a 1,3-relationship to each other. The standard method of preparation of pyrazoles involves such condensations (see Chapter 4.04). With hydrazine itself the question of regiospecificity in the condensation does not occur. However, with a monosubstituted hydrazine such as methylhydrazine and 4,4-dimethoxybutan-2-one (105) two products were obtained the 1,3-dimethylpyrazole (106) and the 1,5-dimethylpyrazole (107). Although Scheme 4 represents this type of reaction as a relatively straightforward process, it is considerably more complex and an appreciable effort has been expended on its study (77BSF1163). Details of these reactions and the possible variations of the procedure may be found in Chapter 4.04. 

Here the other product 4-cyano pyrazole was not formed in the basic medimn. The benzoyl carbonyl is less reactive, and there is no chance for the condensation of hydrazine with it. The H NMR spectra (Table No. 2), IR of the compoimd 4(a-f) characterizes all these 5-aminopyr-azole derivatives. The elemental analysis was in agreement with the proposed structure. IR spectra 4 show absorption bands at 3370 and 3320 cm due to NH2 group and at 1748 cm" due to the presence of carbonyl group. The H NMR of 4 in CDCI3 showed that the NH2 split into two singlets at 6 7.57 and 7.76 exchangeable with D2O. The 4-aromatic p-substituted... 

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