An efficient solvent-free synthesis of NH-pyrazoles from β-dimethylaminovinylketones and hydrazine on grinding

A series of NH-pyrazoles was efficiently synthesized from the reaction of β-dimethylaminovinylketones ([R1C(O)C(R2)CHN(Me2)], where R1 = Me, Ph, 3-MeO-Ph, 4-Me-Ph, 4-MeO-Ph, 4-F-Ph, 4-Cl-Ph, 4-Br-Ph, 4-O2N-Ph, fur-2-yl, thien-2-yl; R2 = H, 2-MeO-Ph; R1, R2 = –(CH2)3C(O)–) and hydrazine sulfate in solid state on grinding in the presence of p-toluenesulfonic acid (PTSA). Most of the reactions proceeded smoothly at room temperature under solvent-free conditions. In comparison with the classical reaction conditions, which employ molecular solvent (ethanol), this new synthetic method has the advantages of shorter times, higher yields, mild reaction conditions as well as being environmentally friendly.