One‐pot synthesis of pyrano[2,3‐c]pyrazole derivatives via two or multicomponent condensation of β‐ketoesters, hydrazine monohydrate/phenyl hydrazine, malononitrile, and substituted benzaldehydes is of great interest not only in synthetic chemistry but also in medicinal chemistry because of the tremendous biological activities, such as anticancer, anti‐inflammatory, analgesic, antimicrobial, and enzyme inhibitory activities exhibited by pyranopyrazoles. This review provides extensive knowledge on novel synthetic methodologies of biologically active non‐spiro/spiro‐pyrano[2,3‐c]pyrazole derivatives published recently.

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Background: The pyrano[2,3-c]pyrazole derivatives are important building blocks of many biologically active compounds owing to their diverse biological potential for example, antiinflammatory, anticancer, antimicrobial and antioxidant properties. Objective: Keeping in mind the wide range of applications of pyrano[2,3-c]pyrazoles, herein we intended to develop a novel synthetic methodology for dihydropyranopyrazole. We were also interested to check the influence of amino acids and dipeptides as catalyst on the synthesis of pyrano[2,3-c]pyrazole derivatives. Method: To achieve our objectives, we used a one-pot multi-component reaction of ethyl 3- oxobutanoate, propanedinitrile, hydrazine monohydrate and several substituted benzaldehydes by using different catalysts and solvents to synthesize our desired products in the presence of various catalysts. Results: We found that optimal conditions for the preparation of pyrano[2,3-c]pyrazoles were L-cysteine (0.5 mol) in the presence of water:ethanol (9:1) at 90 oC. Various 1,4- dihydropyrano[2,3-c]pyrazoles were afforded by using several substituted benzaldehydes in 66-97% yields. Conclusion: We described a green and environmentally benign method to synthesize pyrano[2,3-c]pyrazoles in a one-pot four component reaction of ethyl 3-oxobutanoate, propanedinitrile, hydrazine monohydrate and different substituted benzaldehyde in the presence of L-cysteine in aqueous ethanol (9:1) at 90 oC. Excellent yields of the products, simple work-up, easily available starting materials, use of green solvents, naturally occurring catalyst, non-toxicity, non-chromatographic purification and environmentally benign reaction conditions are some main advantages of this protocol.

Allenes with two carbon–carbon double bonds belong to a unique class of unsaturated hydrocarbons. The central carbon atom of allene is sp hybridized and forms two σ-bonds and two π-bonds with two terminal sp2 hybridized carbon atoms. The chemistry of allenes has been well documented over the last decades. They are more reactive than alkenes due to higher strain and exhibit significant axial chirality, thus playing a vital role in asymmetric synthesis. Over a variety of organic transformations, allenes specifically undergo classical metal catalyzed cycloaddition reactions to obtain chemo-, regio- and stereoselective cycloadducts. This review briefly describes different types of annulations including [2+2], [2+2+1], [3+2], [2+2+2], [4+2], [5+2], [6+2] cycloadditions using titanium, cobalt, rhodium, nickel, palladium, platinum, gold and phosphine catalyzed reactions along with a mechanistic study of some highlighted protocols. The synthetic applications of these reactions towards the synthesis of natural products such as aristeromycin, ent-[3]-ladderanol, waihoensene(−)-vindoline and (+)-4-epi-vindoline have also been described.

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