L-Cysteine Catalyzed Environmentally Benign One-pot Multicomponent Approach Towards the Synthesis of Dihydropyrano[2,3-c]pyrazole Derivatives

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Author(s): Sana Sikandar, Ameer Fawad Zahoor*, Sajjad Ahmad, Muhammad Naveed Anjum, Mirza Nadeem Ahmad, Muhammad Sami Ullah Shah

Journal Name: Current Organic Synthesis

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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.

Keywords: Multicomponent reaction, L-cysteine, organocatalyst, green chemistry, 1, 4-dihydropyrano[2, 3-c]pyrazol

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(E-pub Ahead of Print)
DOI: 10.2174/1570179417666200511092332
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