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Molecules 2005, 10(7), 809-821; doi:10.3390/10070809
Article

3-Formylchromones IV. The Rearrangement of 3-Formylchromone Enamines as a Simple, Facile Route to Novel Pyrazolo[3,4-b]pyridines and the Synthetic Utility of the Latter

1,* , 2, 3, 4, 1, 1 and 2
1 Department of Organic Chemistry Faculty of Natural Sciences, Comenius University, Slovakia 2 Institute of Chemistry, Swietokrzyska Academy, Poland 3 Institute of Chemistry, Faculty of Natural Sciences, Comenius University, Slovakia 4 EML Research, Villa-Bosch, Germany
* Author to whom correspondence should be addressed.
Received: 8 May 2004 / Revised: 4 October 2004 / Accepted: 10 October 2004 / Published: 31 August 2005
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Abstract

One-pot and facile preparations of 6-(2-hydroxy-5-R-benzoyl)-4-methyl-2-R1- pyrazolo[3,4-b]pyridines 4a-o are described, using the reaction of 3-formyl chromones 1 with 5-amino-1-R1-pyrazoles 2. An enamine-intermediate 2-ethyloxy-6-R-3-(3-methyl-1- phenylpyrazol-5-ylaminomethylene)chroman-4-one 3 was isolated at lower temperatures. Acyloxy-derivatives 5 of compounds 4 were obtained by acylation with acid chlorides or acid anhydrides. Coumarins 6 substituted at the 3- and 4-positions were prepared from the pyrazolo[3,4-b]pyridines 4 by condensation reactions and hydrazones 7 were formed from their reaction with 2,4-dinitrophenyl hydrazine. Reactions under microwave irradiation proceeded significantly faster and with high yields.
Keywords: 4-Oxo-4H[1]benzopyrane; Coumarin; Pyrazole; Rearrangement; Enamine; Microwave irradiation 4-Oxo-4H[1]benzopyrane; Coumarin; Pyrazole; Rearrangement; Enamine; Microwave irradiation
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Lacova, M.; Puchala, A.; Solcanyova, E.; Lac, J.; Kois, P.; Chovancova, J.; Rasala, D. 3-Formylchromones IV. The Rearrangement of 3-Formylchromone Enamines as a Simple, Facile Route to Novel Pyrazolo[3,4-b]pyridines and the Synthetic Utility of the Latter. Molecules 2005, 10, 809-821.

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