Abstract
Abstract Pyrazolopyridine and pyrazoloquinoline derivatives were obtained by a one-pot, three-component reaction of arylglyoxals, 3-methyl-1-aryl-1H-pyrazol-5-amines and cyclic 1,3-dicarbonyl compounds in the presence of tetrapropylammonium bromide at 80°C in water through Knoevenagel and Micheal reactions, followed by intramolecular condensation, unexpected dearoylation and oxidation. Mild reaction conditions, high yields, simplicity of work up procedure, starting materials availability and clean product formation are some of the main advantages of this synthetic strategy.
Highlights
We earlier found that the reactions of arylglyoxals 1 with 3-methyl-1-phenyl-1H-pyrazol-5-amine (2) and cyclic 1,3-dicarbonyl compounds 3 carried out under catalyst-free conditions in H2O/EtOH at 80°C afforded 4-aroyl-pyrazolo[3,4-b]pyridine derivatives 4a-h by a one-pot, three-component reaction in excellent yields [23]
It was found that the same reaction in the presence of TPAB as a homogeneous catalyst in H2O/acetone at 80°C gave pyrazolopyridines 5a, 5g-i and pyrazoloquinolines 5b-f as final products in high yields due to unexpected dearoylation occurrence, with no sign of the formation of any 4-aroyl-pyrazolo[3,4-b]pyridine derivatives 4a-h formation (Scheme 1)
After optimizing the reaction conditions, the scope of this reaction was examined with a series of electron rich and electron deficient arylglyoxals and various cyclic 1,3-dicarbonyl compounds [such as cyclopentane-1,3-dione (3a), cyclohexane-1,3-dione (3b), 4,4-dimethylcyclohexane-1,3-dione (3c), dimedone (3d) and indane-1,3-dione (3e)] to form a series of corresponding pyrazolopyridines and pyrazoloquinolines
Summary
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