High speed synthesis of pyrazolones using microwave-assisted neat reaction technology

a high speed, solvent-free, and practical synthesis of pyrazolones under microwave irradiation is described. this greener synthetic methodology involves the reaction of β-keto ester with substituted or unsubstituted hydrazine and provides a simple and straightforward one-pot approach for the synthesis of a variety of pyrazolone derivatives with high regioselectivity. these pyrazolones can exist in different tautomeric forms in solution and the aryl ring of 2-aryl pyrazol-3-ones remain twisted with respect to the pyrazole plane in the crystal state. mechanism of the reaction accounting the regioselectivity has been proposed. one of the pyrazolones obtained via this process was utilized to prepare a spirocyclohexanone derivative of potential biological significance.