1- Acylpyrazoles acids

A-Acylpyrazoles are even weaker bases than the parent pyrazoles they form picrates and perchlorates,217,218,720 but do not dissolve in dilute acids. As mentioned above, the 1-acyl groups are quite labile. Transacylation by aminolysis is readily accomplished by treating various A-acylpyrazoles with strong amines.683, 96,728... 

The iV-acyl group is easily removed in weakly acidic or basic media, especially from those 1 -acylpyrazoles with electron-withdrawing substituents. The kinetics of hydrolysis and aminolysis of variously substituted acylpyrazoles was studied in great detail by Hiittel,102 using ultraviolet spectroscopy. Rate constants were found for both reactions, and an attempt was made to apply Hammett s equation to substituted pyrazoles. 

The ideas for delocalization of nitrogen lone pair electron density into an aromatic or heteroaromatic system were pursued through reduction of acylated pyrazoles and imidazoles to aldehydes in high yield. 3,5-Dimethyl-A -acylpyrazoles are easy to prepare and afford 77-96% yields of aldehydes with LiAlH4 in diethyl ether at 0 Further examples of this reaction have appeared.Although these later publications commented unfavorably on the ability of LiAlH4 to reduce acyl imidazoles to aldehydes (low yields), other workers have demonstrated that yields of 60-80% could be attained at temperatures of -20 to 4-20 °C in diethyl ether.It was considered that the earlier failure may have been caused by the presence of impurities in the acyl imidazoles. The latter are easy to prepare from the parent carboxylic acid and A jV -carbonyldiimidazole. 

Allyl ketones. Reaction of acid chlorides or 1-acylpyrazoles with allylindium bromide in water is a convenient method for synthesis of allyl ketones. The divergent... 

Subst. carboxylic acid amides from 1-acylpyrazoles GON <... 

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