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

Abstract

The pyrano[2,3-c]pyrazole derivatives are important building blocks of many biologically active compounds owing to their diverse biological potential for example, anti-inflammatory, anticancer, anti-microbial and anti-oxidant properties. Keeping in mind the wide range of applications of pyrano[2,3-c]pyrazoles, herein we intended to develop a novel synthetic methodology for dihydropyranopyrazoles. We were also interested in determining the influence of amino acids and dipeptides as a catalyst on the synthesis of pyrano[2,3-c]pyrazole derivatives. 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. 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 °C. Various 1,4-dihydropyrano[2,3- c]pyrazoles were afforded by using several substituted benzaldehydes in 66-97% yields. 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.