Synthesis of 6-Amino-2,4-dihydropyrano[2,3-c]pyrazol-5-carbonitriles Catalyzed by Silica-Supported Tetramethylguanidine Under Solvent-Free Conditions

Abstract

An efficient, high-yielding, and rapid protocol has been developed for the synthesis of diversity-oriented 6-amino-2,4-dihydropyrano[2,3-c]pyrazol-5-carbonitriles derivatives via a four-component, one-pot cyclocondensation reaction of ethyl acetoacetate, hydrazine hydrate, aldehydes, and malononitrile using silica-supported tetramethylguanidine as a heterogeneous catalyst for the first time. The protocol proves to be efficient and environmentally benign in terms of very easy workup, good yields, and ease of recovery of catalyst. In addition, the present method is superior in terms of green media, the amount of catalyst, and reaction time.

GRAPHICAL ABSTRACT

Keywords:

• Four-component reaction
• heterogeneous catalyst
• pyrano[2,3-c]pyrazole
• silica-supported tetramethylguanidine

Notes

^a Reaction conditions: hydrazine hydrate (1.5 mmol), ethyl acetoacetate (1 mmol), benzaldehyde (1 mmol), malononitrile (1 mmol), and catalyst (10 mol%, except entries 13, 14, and 15).

^b Isolated yield.

^a Reaction conditions: hydrazine hydrate (1.5 mmol), ethyl acetoacetate (1 mmol), aldehydes (1 mmol), malononitrile (1 mmol), and SiO₂TMG catalyst (10 mol%).

^b Isolated yield.

^a Reaction conditions: Phenyl hydrazine/hydrazine hydrate (1.5 mmol), ethyl acetoacetate (1 mmol), aldehydes (1 mmol), malononitrile (1 mmol), and SiO₂TMG catalyst (10 mol%).

^b Isolated yield.

^a Isolated yield.

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