Current Microwave Chemistry - Volume 8, Issue 3, 2021

Background: Microwave-assisted domino cyclization reactions have attracted great interest for researchers to synthesize complex compounds in shorter times with increased yields. The domino reactions were used in various synthetic approaches and many drug deliveries in medicinal chemistry with microwave-assisted approaches. Methods: Microwave irradiation has been applied for various domino reactions. The research related to microwave-assisted domino cyclization was reviewed and the important methodologies were collected from 2011-2021. Results: Only those methodologies that involve microwave-assisted domino cyclization reactions during synthesis in a related manner have been reviewed. Along with some recent syntheses that are microwave-assisted regarding new heterocyclic moieties are summarized. Conclusion: Microwave-assisted domino cyclization reactions can be employed to quickly explore and increase molecular diversity in synthetic chemistry. We hope that this review will be helpful to find out complex molecule synthesis by microwave-assisted domino cyclization reactions. This review aimed to explain the applications of microwaves for the domino reactions from 2011- 2021. In this respect, microwave-mediated methods help researchers to make helpful studies.

Organocatalysis is a term used to describe small organic molecules that exclusively include carbon, hydrogen, oxygen, nitrogen, sulphur, and phosphorus atoms that are used to speed up chemical reactions. The researchers demonstrated a large area of applications in various organic transformations catalysed by the organocatalysts due to their lower moisture sensitivity in air, easy abundance, less polluting nature, noninterference with the final product, and costeffectiveness. This highlights high demand and direct benefits in pharmaceutical intermediate and fine chemical manufacturing compared to other conventional transition metal and enzyme catalysts. This review article intends to compile literature-reported applications of the microwave accelerated organocatalyzed carbon-carbon and carbon-heteroatom bond formation reactions.

The synthesis of heterocyclic compounds via carbon-nitrogen (C-N) bond formation reaction is considered an emerging and efficient protocol in the field of synthetic chemistry. The C– N bond-forming reactions can proceed through condensation, coupling, ring-opening, cyclization, or ring closure process, etc. The reactivity pattern of these reactions mainly depends upon the reaction conditions, as well as the type of catalysts and reacting substances that are associated with the synthesis of heterocyclic compounds containing the C-N system, including pyrazole, imidazole, pyridine, pyrimidine, thiazole, tetrazole, isoxazole, benzothiazine, and benzimidazole, etc. Further, the technique of microwave-induced synthesis becomes an alternative strategy for the sustainable production of structurally diverse organic compounds. This method provides a cleaner reaction, faster reaction rate, atom economy, and energy-efficiency. Therefore, the utilization of microwave radiation in organic synthesis becomes resource-friendly and eco-friendly proces. It follows the green chemistry approach by using safer solvents, renewable starting materials, and green catalysts. The unique feature of this method is to generate various types of bioactive or medicinal agents.

Background: Schiff bases play a key role in the generation of a large number of biologically active compounds via cycloaddition, replacement, and ring closure reactions. Objective: The objective of this study is to optimize the purity and yield of the product, improve the reaction time, and make the reaction more eco-friendly with the help of microwave-assisted organic synthesis. Methods: New series of Schiff’s bases of triazole derivatives were achieved via multicomponent reactions. The starting material benzohydrazide 1 was obtained by esterification of benzoyl chloride with methanol in the presence of concentrated sulphuric acid, followed by the reaction with hydrazine hydrate. Benzohydrazide was allowed to react with carbon disulphide in ethanolic potassium hydroxide solution to yield potassium dithiocarbazinate 2, which undergoes cyclization by reacting with hydrazine hydrate to afford 4-[amino]-5-phenyl-4H-1,2,4-triazole-3-thiol (3). Further, various Schiff’s bases, 4a-f, were obtained by reacting 1,2,4-triazole-3-thiol with different substituted benzaldehydes under microwave irradiations as a green and eco-friendly energy source. Results: The structures of the newly synthesized compounds were elucidated in accordance with their spectral data and elemental analysis. Conclusion: The obtained compounds exhibited significant in vivo anti-diabetic activity as compared to the standard drug Metformin. The anti-diabetic effect was investigated by using the Alloxan-induced diabetic model.