Steric and Electronic Control in the Addition of Hydrazine and Phenylhydrazine to α-[(Dimethylamino)methylene]-β-oxoarylpropanenitriles

Reaction of hydrazine with α-[(dimethylamino)methylene]-β-oxoarylpropanenitriles 2 gives a mixture of the 4-aroyl-5-aminopyrazoles 3 and the 5-aryl-4-cyanopyrazoles 4. Similarly reaction of 2 with phenylhydrazine gives rise to the 5-amino-4-aroyl-1-phenylpyrazoles 5 and 5-aryl-4-cyano-1-phenylpyrazoles 6. The regioselectivity of addition has been investigated with respect to the electronic nature and steric requirements of the aromatic substitution. The ratio of products was found to be independent of the electronic nature of the substituent. The outcome of the reaction was however very sensitive to steric factors. Substituents in the para- and meta-positions favoured formation of the pyrazole-nitrile products 4 and 6, whereas sterically demanding ortho-substituents favoured the pyrazole-amino ketones 3 and 5.

The regioselectivity of addition of hydrazines to α-[(dimethylamino)methylene]-β-oxoarylpropane nitriles is under steric rather than electronic control