Current Microwave Chemistry - Volume 5, Issue 3, 2018

Background: Microwave heating has been shown to be an invaluable technology for medicinal chemistry and drug discovery applications. Recently, it has been used for heterocyclic synthesis increasingly. This review article shows a work on the synthesis of coumarin derivatives by microwave- assisted heating. Methods: Microwave-assisted heating has been used for the synthesis of coumarin derivatives. There are some useful methods to obtain coumarin derivatives. The Knoevenagel condensation is the most prominent one with microwave heating. The other one is the microwave-assisted Vilsmeier-Haack reaction. Another one is microwave assisted convenient one-pot synthesis of coumarin derivatives via Pechmann condensation catalyzed by FeF3 under solvent-free conditions. In addition to these, Perkin condensation can also be used for the synthesis of coumarin derivatives under microwave heating conditions. Results: Coumarin derivatives have a pharmacological importance in drug discovery and dyes. Microwave irradiation is an effective method for the synthesis of coumarin derivatives and when compared to the conventional heating, it has many advantages. Conclusion: This review aimed to demonstrate the applications of microwave heating for the synthesis of coumarin derivatives from 2007 to 2018. It may be helpful to synthesize new coumarin derivatives as an alternative method that enables you to gain time and a new perspective.

Microwave-assisted solvothermal synthesis (MASS) has emerged as an effective method for the preparation of targeted organic molecules, coordination clusters and infinite networks and minerals. Different types of coordination clusters, one dimensional (1D) chains, two-dimensional (2D) layers and three-dimensional (3D) frameworks have recently been synthesized – in high yields, short reaction times, and improved uniformity. The success is due to uniform heating by the microwave radiation. In this minireview, we intend to demonstrate the advantages of MASS compared to solvothermal synthesis using traditional heating ovens in the preparation of disk and cube coordination clusters as typical examples. There is great variability for the key peripheral ligands as well as inner bridges in the formation of disk and cube clusters, which affect not only the symmetry, weak interaction, packing mode of the clusters, but also the effectiveness of microwave synthesis. In addition, the success in the preparation of several novel polynuclear clusters broadens the practicability of microwave assisted reactions.

Background: This paper describes the synthesis of four novel fused heterocycles from the condensation reaction of chalcone derivatives with amino derivatives. Herein we describe the synthesis of twelve compounds by both conventional and microwave method. The synthesized compounds are excellent in utilizing microwave irradiation rather than conventional heating. Methods: Synthesis of substituted heterocycles was carried out under microwave radiation and conventional heating. Results: The comparison study between the microwave and conventional synthesis proved that microwave synthesis is the best and it is a current lead in Organic synthesis. In anti-convulsant evaluation, compounds IIa, IIIa, IVa produced a significant activity by the abolition of extensor phase. In the anti-inflammatory evaluation, compounds IIb and IIc produced a significant activity due to the presence of the pyrazoline nucleus. Conclusion: In an experimental procedure, 4- acetamido phenol was reacted with an aromatic aldehyde to give chalcones. These chalcones on cyclization and condensation with hydrazine hydrate, thiourea, guanidine nitrate gave pyrazolines, aminopyrimidines, and pyrimidine thiones, respectively The compounds were subjected to anti-convulsant and anti-inflammatory evaluation.

Background: Currently, new chemical entities developed as anticancer agents against tubulin as a protein target. The present work, a quinazoline derivatives were used to design and synthesized by microwave irradiation as an anticancer agent through selective inhibitors of colchicinebinding site of tubulin by the molecular docking of quinazoline derivatives using Schrödinger, LLC, New York, NY, 2017. Methods: Seven of quinazoline derivatives were docked into colchicine-binding site of tubulin with PDB code 5OSK. Results: The interaction was evaluated based on the re-ranked score comparison between quinazoline derivatives with 3,4-dihydroquinazolin-2(1H)-one. The title compounds show similar type of hydrogen bond interaction; however, the compound 4a with good binding energy and RMSD interacted with THR: A179 and LYS B: 352 through NH and CO of acetamido group.

Background: Agro-waste derived extracts such as Water Extract of Banana (WEB), Water Extract of Rice Straw Ash (WERSA), and Water Extract of Papaya Bark Ash (WEPBA) have been recently demonstrated to be green method syntheses of some important bioorganic molecules. Such a green method terminated the use of the expensive, pollution-causing, hazardous, and toxic materials during the reaction. Coumarin-3-carboxylic acid represents a class of naturally/synthetic occurring compound with a wide range of pharmacological applications. In this paper, we demonstrated a novel and easy Knoevenagel condensation product by the reaction of salicylaldehyde (1) and Meldrum’s acid (2) catalyzed by Water Extract of Lemon Fruit Shell Ash (WELFSA) as a greener method under microwave irradiation. The reaction was completed in 2-6 min giving a final product isolation by simple workup in excellent yield with column chromatography free pure form. The product was characterized by FT-IR, 1H-, 13C-NMR and mass spectrometry techniques. Methods: Agro-waste extract as a greener reagent was used for the synthesis of 2-oxo-2H-chromene- 3-carboxylic acid under microwave irradiation method. Results: Knoevenagel condensation of salicylaldehyde (1) and Meldrum’s acid (2) was conducted catalyzed by WELFSA acting as a natural base. Firstly, the catalyst was capable to extract acidic proton from Meldrum’s acid followed by nucleophilic substitution on salicylaldehyde carbonyl group. Further, the elimination of water and acetone took place and by ring closure, resulted in a target product coumarin-3-carboxylic acid. Conclusion: We have demonstrated agro-waste extract to be an alternative green catalyst for the condensation of substituted salicylaldehyde and Meldrum’s acid. The method has advantages of being solvent-free, non-polluting, non-toxic, using cheaper catalyst, simple reaction condition and environment-friendly. The final product isolated was chromatographically pure and did not require further purification. The catalyst derived is natural and inexpensive, available in a large amount of agro-waste generated in kitchens. The method is a suitable example of a green chemistry protocol.

Background: In the present study, we performed according to green chemistry’s standards, an easy and very efficient one-pot synthesis of2-thioxo-1,3-thiazolidin-4-one(rhodanine) and thiazolidine-2,4-dione (TZD) derivatives via Knoevenagel condensation of various aldehydes with rhodanine/ thiazolidine-2,4-dione in the presence of only 15 mole% of deep eutectic solvents (DESs) -choline chloride/urea- propionate and microwave radiation under solvent-free conditions. Method: Twenty compounds were synthesized under thermal and microwave conditions and the yields of synthesized compounds were 77-90% and 81-95%, respectively. The IR spectra were obtained on a PerkineElmer FT-IR spectrophotometer using KBr disks.1H NMR and 13C NMR of products were registered Bruker 500 spectrometer and chemical shifts are expressed as d (ppm) with tetramethylsilane (TMS) as an internal standard in DMSO-d6 as a solvent. The purity of synthesized compounds was checked by chromatography and UV light (254 nm) was used for visualization. Result: A range of rhodanine and -2, 4-thiazolidinedione derivatives were synthesized using ChCl/ urea catalyst under solvent -free conditions at 80°C. Then, the sample derivatives were synthesized under optimum conditions. Conclusion: The mild reaction conditions, good to excellent yields, easy workup, without the involvement of any harmful solvents/chemicals and easily available substrates, they all facilitated in the preparation of all synthesized compounds.