Minimizing Side Reactions in Classical Pyrazole Synthesis from β - Oxonitriles: The Use of Acetylhydrazine

A new two-step, one-pot alternative protocol for preparation of 1H-pyrazole-5-amines from 3-oxoalkanenitriles utilizing readily available acetylhydrazine has been developed. Typical by-products formed in traditional reactions of 3- oxoalkanenitriles with hydrazine are not formed when the present method is used, thus facilitating purification on a large scale. The method was used to prepare a medicinally important heterocycle on a kilogram scale.