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Multi-Component Synthesis of Pyrazolopyridopyrimidines
E. A. Muravyova, S. V. Shishkina, V. I. Musatov, I. V. Knyazeva, O. V. Shishkin, S. M. Desenko, V. A. Chebanov*
State Scientific Institution ‘Institute for Single Crystals’ of National Academy of Sciences of Ukraine, Kharkiv, Ukraine
22 June 2009 (online)
Reported here is the three-component cyclocondensation of 5-aminopyrazoles 1 or 5, barbituric acids 2 and aromatic aldehydes 3 to give tricyclic compounds 4 and 6. When N-alkyl- or N-arylpyrazoles were used as the substrates, aromatized structures 4 were obtained in moderate to excellent yields under either conventional or microwave heating. However, when the N-H pyrazoles were used, the dihydropyridines 6 were formed. A four-component reaction was also demonstrated to give symmetrical or unsymmetrical spirocycles 7 and 8.