Abstract

A series of 6-amino-4-substituted-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles 5(a-j) as a potent anticancer agent were synthesized via one-pot, four-component condensation reaction of aryl aldehydes, ethyl acetoacetate, malononitrile, and hydrazine hydrate in solvent-free conditions using ionic liquid [Et3NH][HSO4] as an efficient, eco-friendly and reusable catalyst. The Multi component coupling reactions (MCRs) indicate a highly appreciated synthetic tool for the establishment of novel and complex molecular scaffold with a minimum number of synthetic steps with the advantage like shorter reaction times, lower costs, high degrees of atom economy etc. From the literature survey it is found that dihydropyrano[2,3-c]pyrazole derivatives posses very important biological activities, including anticancer, antiinflammatory, antimicrobial, inhibitors of human Chk1 kinase, molluscicidal, and insecticidal activities. The solvent used in conventional organic synthesis are suffered by many disadvantage like environmental hazards, toxicity, volatile nature, expensive etc. A new term ‘designer solvents’ referring to Ionic liquids because of their adjustable physical and chemical properties with the change in selected cationic and anionic combination. Ionic liquids have become a promising alternative media for various chemical processes due to their properties including good solvating capability, negligible vapour pressure, non-inflammability, ease of recyclability, controlled miscibility and high thermal stability. Herein we are reporting the use of acidic Bronsted ionic liquid(ABILs) [Et3NH][HSO4] triethyl ammonium sulphate for the synthesis of biologically important scaffold 6-amino-4-(substituted phenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile . Compared to other methods, this new method has advantages, such as excellent yields, a short reaction time, mild reaction conditions and catalyst reusability. The synthesized derivatives 5(a-j) were characterized by FTIR, 1HNMR, 13CNMR and mass spectral data.

Highlights

  • All the final compounds (5a-5j) were synthesised following the procedure depicted in scheme I.Synthesis is carried out in one pot by adding all the reactant at a time with equimolar ratio as substituted aromatic aldehyde(1mmol),malononitrile(1mmol),hydrazine hydrate(1mmol)and ethyl acetoacetate(1mmol) initially, the reaction was carried out in the absence of the catalyst; no product is obtained so catalyst is added increasing amount to determine the appropriateconcentration of the catalyst and solvent [Et3NH][HSO4], we investigated the model reaction atdifferent concentrations of [Et3NH][HSO4], such as 0,5, 10, 15, 20 and 25 mol%

  • The dihydropyrano[2,3-c]pyrazole formed in 0,50,65,70,94 and 85 % yields, respectively(Table 2).The increase in concentration of catalyst from 20 to 25 mol% does not increase the yield of product. This indicates that 20 mol% of [Et3NH] [HSO4] is sufficient forthe reaction by considering the product yield

  • With extreme high literature survey of all available method of multi component one pot cyclo condensation synthesis of 6-amino-4-(substituted phenyl)-3-methyl-2,4-dihydropyrano[2,3-c] pyrazole-5-carbonitrile as far as our genuine knowledge first time we are introducing the use of this green medium i.e. Acid Bronsted

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Summary

Graphical Abstract

The Multicomponent coupling reactions (MCRs) indicate a highly appreciated synthetic tool for the establishment of novel and complex molecular scaffold with a minimum number ofsynthetic steps with the advantage like shorter reaction times, lower costs, high degrees of atom economy etc.With the literature survey it is found that dihydropyrano[2,3c]pyrazole derivatives possess very important biological activities, including anticancer, antiinflammatory, antimicrobial, inhibitors of human Chk kinase, molluscicidal, and insecticidal activities. We are introducing first time the use of acidic Bronsted ionic liquid(ABILs)[Et3NH][HSO4] triethyl ammonium sulphate for the synthesis of biologically important scaffold 6-amino-4-(substituted phenyl)-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitrile,the synthesised derivatives subjected to anticancer activity. This new method consistently has advantages, including excellent yields, a short reaction time, mild reaction conditions and catalyst reusability We are reporting synthesis of 6-amino-4-substituted-3-methyl-2,4-dihydropyrano[2,3-c]pyrazole-5-carbonitriles5(a-j) with excellent yield at room temperature using Ionic liquid [Et3NH][HSO4] as catalyst as well as solvent and introducing one more novel green chemistry protocol in the list of methods of synthesis for pyrano[2,3-c]pyrazole derivatives as important biologically active scaffold

Results and discussion
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