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Molecules 2010, 15(9), 6619-6629; doi:10.3390/molecules15096619
Article

Green One Pot Solvent-Free Synthesis of Pyrano[2,3-c]-Pyrazoles and Pyrazolo[1,5-a]Pyrimidines

1,* , 2, 1 and 1
Received: 26 July 2010 / Revised: 13 August 2010 / Accepted: 26 August 2010 / Published: 20 September 2010
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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.
Keywords: pyranopyrazole; multi-component synthesis; aminopyrazolinone; pyrazolo[1,5-a]pyrimidine; cyanoacetic acetic anhydride; NOE difference experiments pyranopyrazole; multi-component synthesis; aminopyrazolinone; pyrazolo[1,5-a]pyrimidine; cyanoacetic acetic anhydride; NOE difference experiments
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Al-Matar, H.M.; Khalil, K.D.; Adam, A.Y.; Elnagdi, M.H. Green One Pot Solvent-Free Synthesis of Pyrano[2,3-c]-Pyrazoles and Pyrazolo[1,5-a]Pyrimidines. Molecules 2010, 15, 6619-6629.

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