Ultrasonic-accelerated rapid protocol for the improved synthesis of pyrazoles

Abstract

A simple, catalyst-free, green synthetic protocol is described for the one-pot synthesis of pyrazoles via multicomponent reaction of aromatic aldehydes, hydrazine monohydrate and ethyl acetoacetate and malononitrile/ammonium acetate in water under ultrasound irradiation. This protocol avoids traditional chromatography and purification steps and it affords highly selective conversion with no byproducts.

Nano-CuCr2O4: An Efficient Catalyst for a One-Pot Synthesis of Tetrahydrodipyrazolopyridine

“…Our method is shown in Scheme 1 which shows the ratios of reactants used. (Incidentally, we were able to compare our results with those of a recent report, 21 in which a similar series of dipyrazolodihydropyridine derivatives were synthesised using the same set of reactants, but ultrasound was used instead of a catalyst. )…”

A convenient synthesis of pyrandione derivatives using P-toluenesulfonic acid as catalyst under ultrasound irradiation

“…In the literature, it is shown that increase in yield is observed upon condensation reaction using ultrasounds. A large number of reactions can be carried out in higher yield [6,[16][17][18][19][20][21][22]. Consequently, we chose to examine the effect thereof on the synthesis of Schiff bases.…”

An Efficient and Eco‐Friendly One‐Pot Synthesis of Pyrazolopyridines Mediated by Choline Chloride/Urea Eutectic Mixture

“…The construction of the pyrazolopyridine nucleus is mainly performed by a 1,3‐dipolar cycloaddition reaction of azomethine imines and alkynes, or by cyclocondensation of aminoazoles and aminoazines with several carbonyl compounds including α,β‐unsaturated ketones, β‐halovinyl aldehydes, 1,3‐diketones among others . Recently some authors have described the synthesis of tetrahydrodipyrazolopyridine derivatives via multicomponent reaction (MCR) of ethyl acetoacetate, hydrazine, aromatic aldehydes and ammonium acetate under catalyst free, and ultrasound conditions, and also employing homogeneous and heterogeneous catalysts . Despite the diverse synthetic efforts toward the obtention of this heterocycle, some methodologies are associated with limitations like a laborious preparation of catalyst, moderate yields and longer reaction times.…”