Green One Pot Solvent-Free Synthesis of Pyrano23-c-Pyrazoles and Pyrazolo15-aPyrimidines

摘要

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.