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Oxygen-containing heterocycles are largely distributed in natural and synthetic compounds. Coumarins are among the most famous heterocycles which possess one oxygen atom in their rings. Coumarins are classified as multifunctional scaffold and are used as anti-oxidant reagents, anti-inflammatory, anti-microbial, anti-fungal, anti-HIV active, analgesic, anti-histaminic, insecticides, dyes, herbicides, sensitizers, perfumes, cosmetics and food additives. Due to their diverse applications in industrial and pharmaceutical fields, many chemists have given significant interest to these compounds. Herein, the review highlights various methods for the synthesis and interactions of coumarin moiety as one of the most efficient categories of heterocycles.

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The reaction of 3-amino-4,6-dimethylthieno[2,3-Ä]pyridine-2-carboxamide (la) or its N-aryl derivatives lb-d with carbon disulphide gave the pyridothienopyrimidines 2a-d, whilst when the same reaction was carried out using yV 1 -arylidene-3-amino-4,6-dimethylthieno[2,3-Ä]pyridine-2-carbohydrazides (le-h), pyridothienothiazine 3 was obtained. Also, refluxing of lb-d with acetic anhydride afforded oxazinone derivative 4. Com pounds 2a and 2b-d were also obtained by the treatment of thiazine 3 with ammonium acetate or aromatic amines, respectively. When compound 2a was allowed to react with arylidene malononitriles or ethyl acyanocinnamate, novel pyrido[3",2":4',5']thieno [3',2':4,5]pyrimido[2,l-Ä][l,3] thiazines 5a-c were obtained. Treatment of 2b-d with bromine in acetic acid furnished the disulphide derivatives 6a-c. U.V. irradiation of 2b-d resulted in the formation of pyrido[3",2":4',5']thieno[3',2':4,5]pyrimido[2,l-Ä]benzthiazoles 7a-c. The reaction of 2a-d with some halocarbonyl compounds afforded the corresponding S-substituted thiopyrido thienopyrimidines 8a-j. Compound 8b was readily cyclized into the corresponding thiazolo[3",2"-a]pyrido[3',2':4,5]thieno[3,2-c/]pyrimidine 9 upon treatment with cone, sulphuric acid. Heating of 2a,b with hydrazine hydrate in pyridine afforded the hydrazino derivatives lla,b. Reaction of ester 8c with hydrazine hy drate in ethanol gave acethydrazide 10. Compounds 10 and lla,b were used as versatile synthons for other new pyridothienopyrimidines 12-15 as well as [1,2,4] triazolopyridothienopyrimidines 16-19.

The pyrazolopyrazine ring system is a very interesting class of heterocyclic compounds that were considered as important scaffolds of many efficacious biologically active agents that show anticancer with low toxicity, antioxidant, anticonvulsant, antiparasitic, anti‐inflammatory, antiviral, antibacterial, antifungal, and analgesic activities. This review throws light on the detailed synthetic approaches for the synthesis and reactions of pyrazolopyrazine moiety. This follow up may encourage the chemists to generate new routes possessing pyrazolopyrazine nucleus with high efficacy.