A3-Pyrazolines

The electrochemical oxidation of 4-dimethylaminoantipyrine (4-dimethyl-amino-2,3-dimethyl-l-phenyl-A3-pyrazolin-5-one) has been investigated in CH3CN-NaC104 at a glassy carbon electrode.421 The first step is a quasi-reversible electron transfer from the lone-pair electrons on the 4-dimethyl-amino nitrogen to form the radical-cation. The second-order disappearance of the radical-cation is presumably due to a disproportionation reaction. The oxidation at the potential of the plateau of the first wave gave the protonated 4-dimethylaminoantipyrine in 60% yield, but other products were not identified. 

Reduction of one or two double bonds in the azole ring gives nonaromatic systems. Historically, these derivatives have been described as azolines and azolidines, as illustrated by the pyrazole derivatives 25 and 26. In 3-pyrazoline 25 the 3 indicates the first ring atom associated with the double bond . In the older literature the position of the double bond is indicated by An, where n is the number of the first ring atom associated with the double bond, e.g., A3-pyrazoline 25. Alternatively, they are named as dihydro or tetrahydro derivatives of the parent azole (e.g., 2,5-dihydropyrazole 25) and this nomenclature is IUPAC-preferred nomenclature for rings with more than two heteroatoms . 

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