Microwave-Accelerated Facile Synthesis of 1H-Pyrazolo[1,2-b]Phthalazine-5,10-Dione Derivatives Catalyzed by WEMPA

Synthesis of bioactive scaffolds catalyzed by agro-waste-based solvent medium

The backbone of synthetic organic chemistry is the formation of carbon–carbon and carbon–heteroatom bonds. Scientists are actively working to develop new methods of bond-forming reactions because it is one of the most useful tools for the development of structurally diverse molecular entities. On the other hand, scientists are constantly discovering chemical processes to make them more sustainable in order to avoid the ever-increasing chemical emission associated with hazards to the environment. Thus, the development of greener catalytic reactions demonstrated a massive uptick in the ability to carry out carbon–carbon and carbon–heteroatom bond-forming reactions under environmentally friendly and simple reaction conditions. Various approaches are demonstrated, namely, solvent-free, microwave irradiation, ionic liquids, ball milling, ultrasound, one-pot, and aqueous-mediated methods under green chemistry protocol. Agro-waste is the postharvest part or agricultural residues derived from various agricultural activities, which has diverse scope and applications. The use of this agro-waste is an eco-friendly and cost-effective process of waste management. Appropriate and optimal utilization of these waste by-products is one of the major challenges in the present days. The recent trend around the globe is to transform waste into wealth concepts to achieve various applications. Agro-waste-derived ashes and extracted medium are successfully studied recently as a heterogeneous- or homogenous-based catalyst in various organic transformations. Agro-waste-derived catalysts are easily available, cost-effective, simple to prepare, nontoxic, easy to handle, biodegradable, and more environmentally benign. This article focuses more on a few instances of agro-waste-based homogeneous and heterogeneous organic synthesis, especially those used in the construction of bioactive molecule synthesis via C–C and C–X bond formation reactions are discussed. The compiled literature in this article is based on keywords used in the search engine on “agro-waste-based catalyst for organic transformations”, and review articles published on this topic, future scope, and summary are discussed.

Superparamagnetic Polyaniline-co-m-phenylenediamine@Fe3O4 Nanocomposite as an Efficient Heterogeneous Catalyst for the Synthesis of 1H-pyrazolo [1,2- a]pyridazine-5,8-diones & 1H-pyrazolo[1,2-b]phthalazine-5, 10-diones" Instead of 1H-pyrazolo[1,2-b] Phthalazinedione Derivatives

BACKGROUND

The use of polymer-based catalysts has increased because of their high potential application as an effective catalyst in organic reactions. They have benefits such as high efficiency and reactivity, simple separation, and safety compared to other heterogeneous catalysts.

AIM AND OBJECTIVE

The objective of the current research is to prepare solid polymer-based catalysts, poly(aniline-co- m-phenylenediamine) (PAmPDA), and its superparamagnetic nanocomposite. Then, the catalytic activity of the resulting superparamagnetic nanocomposite was investigated in the synthesis of 1H-pyrazolo[1,2-b]phetalazine-5,10-diones and 1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives. A series of some 1H-pyrazolo[1,2-b]phetalazine-5,10-diones and 1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives was tested for its antibacterial properties against the Staphylococcus aureus and E.coli bacteria.

MATERIALS AND METHODS

PAmPDA copolymer was synthesized in a 1:2 molar ratio of Ani to mPDA via radical oxidative polymerization at room temperature. Superparamagnetic PAmPDA@Fe3O4 nanocomposite was synthesized from a mixture of Fe(II), Fe(III) solution, and PAmPDA copolymer via the in-situ co-precipitation technique. 1H-pyrazolo[1,2-b]phetalazine-5,10-diones were synthesized via one-pot three-component condensation reaction of Phthalhydrazide, aromatic aldehyde derivatives, and malononitrile in the presence of PAmPDA under solvent-free conditions at 80 °C. The synthesis of 1Hpyrazolo[1,2-a]pyridazine-5,8-dione derivatives was carried out via a one-pot three-component condensation reaction of maleic hydrazide, aromatic aldehyde derivatives, and malononitrile in the presence of PAmPDA under reflux conditions at EtOH/H2O 1:1. The antibacterial activity of some derivatives was tested against Gram-positive and Gram-negative bacteria.

RESULTS

First, superparamagnetic PAmPDA@Fe3O4 nanocomposite was synthesized and characterized successfully, and then the resulting nanocatalyst was used for the synthesis of pyrazolo[1,2-b]phthalazine and pyrazolo[1,2-a]pyridazine. We obtained the maximum yield of the desired 1H-pyrazolo[1,2- b]phthalazine-5,10 dione derivatives with 0.05 g of catalyst at 80°C, under solvent free conditions, whereby the reaction was complete within 30 min. A wide range of 1H-pyrazolo[1,2-b]phthalazine-5,10 dione derivatives were synthesized in good to excellent yield. On the other hand, pyrazolo[1,2- a]pyridazine derivative was synthesized successfully in high yield using PAmPDA as a nanocatalyst. The antibacterial activity of some derivatives, according to the data (inhibition zone%), showed good activity against Staphylococcus aureus and E.coli.

CONCLUSION

In this research, PAmPDA was used for mild preparation of 1H-pyrazolo [1,2-a]pyridazine5,8-diones & 1H-pyrazolo[1,2-b]phetalazine-5,10-diones derivatives with excellent yields and short reaction times. The attractive features of this protocol are simple procedure, cleaner reaction, and the use of recyclable nanocatalyst. Satisfactory yields of products and easy workup make this a useful protocol for the green synthesis of this class of compounds. The antibacterial activity of some derivatives, according to the data (inhibition zone%), showed good activity against Staphylococcus aureus and E.coli.