Abstract
Pyrano[2,3-c]pyrazoles are obtained via mixing ethyl acetoacetate, hydrazine hydrate, aldehydes or ketones and malononitrile in the absence of solvent. These same products were also obtained by reacting arylidenemalononitriles 3 with 3-methyl-2-pyrazolin-5-ones. NOE difference experiments confirmed that these products exist solely in the 2H form. Similar treatments of 3-amino-2-pyrazolin-5-one with arylidene-malononitrile afforded adduct 6. Similarly mixing ethyl cyanoacetate, hydrazine hydrate, aldehydes, with malononitrile gave the same product 6. A novel synthesis of 4-oxo-4H-pyrano[2,3-c]pyrazole (8) could be achieved via reacting 3-methyl-2-pyrazolin-5-one with a mixture of cyanoacetic acid and acetic anhydride. Similar treatment of 3-aminopyrazole 11 with the benzylidene-malononitrile produced the pyrazolo[2,3-a]pyrimidines 12a,b.
Highlights
The considerable biological activities of 2-amino-4-substituted pyrano[2,3-c]pyrazole-3carbonitriles 1, have stimulated considerable research directed for synthesis of derivatives of this ring system
We became interested to see if the multi-component synthesis of 1 can be extended to enable synthesis of other substituted pyranopyrazoles and if the products are obtained this way in yields comparable to those originally obtained
In the same time we have looked into a report in the literature [12] of the isolation of acyclic adducts 5 from reaction of 3-methyl pyrazoline-5-one 2
Summary
The considerable biological activities of 2-amino-4-substituted pyrano[2,3-c]pyrazole-3carbonitriles 1, have stimulated considerable research directed for synthesis of derivatives of this ring system. These compounds were first obtained by H. We used NOE difference experiments to establish that these products exist in the 2H form in DMSO solutions [14]. We became interested to see if the multi-component synthesis of 1 can be extended to enable synthesis of other substituted pyranopyrazoles and if the products are obtained this way in yields comparable to those originally obtained. This work enabled us to introduce an efficient approach for the synthesis of pyranopyrazoles that could be shown via NOE difference experiments to exist in the 2H form. The one step synthesis approach seems to offer an attractive green methodology that saves both solvent and time compared to the multi-step approach
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