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was examined by the reaction of several substituted aryl aldehydes
with 2,3-diaminopyridine. The results are shown in Table 2. The
newly synthesized compounds were compared (mp, MS, NMR,
and IR) with compounds that were prepared by using the literature
method11 (Scheme 2). This comparison revealed that the com-
pounds synthesized by this newly developed method were exactly
similar in all aspects to the reference compounds.
In conclusion, we have developed a new, facile, and efficient
methodology for the eco-compatible preparation of 2-substi-
tuted-1H-imidazo[4,5-b]pyridine from 2,3-diaminopyridine and
aldehydes in an aqueous medium. The use of water as a solvent
and easy reaction conditions to deliver the target products in good
yields, often in analytically pure form, suggest a good applicability
of this process. We have also shown the versatility of this method-
ology by applying it to a wide variety of aldehyde substrates. To the
best of our knowledge, this is the first report on the synthesis of
1H-imidazo[4,5-b]pyridine derivatives in aqueous medium.
General procedure for synthesis of title compounds 3a–o: A mix-
ture of 2,3-diaminopyridine (1) (10 mmol) and substituted aryl
aldehyde (2a–o) (11 mmol) in water was heated at 100 °C for
10–12 h. The progress of the reaction was followed by TLC (dichlo-
romethane/methanol; 9:1). The reaction mixture was cooled to
room temperature, and the product was collected by filtration,
washed with water, and suck dried. The product was recrystallised
from ethanol to give title compounds (3a–o) in 83–87% yields.
14. Singh, M. P.; Sasmal, S.; Lu, W.; Chatterjee, M. N. Synthesis 2000, 10, 1380–
1390.
15. Ryabukhin, S. V.; Plaskon, A. S.; Volochnyuk, D. M.; Tolmachev, A. A. Synthesis
2006, 21, 3715–3726.
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Acknowledgments
18. Jadhav, G. R.; Shaikh, M. U.; Kale, R. P.; Gill, C. H. Chin. Chem. Lett.. doi:10.1016/
j.cclet.2008.09.057.
The authors are thankful to the Head, Department of Chemistry,
Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, for
providing laboratory facilities and for the valuable support.
19. Jadhav, G. R.; Shaikh, M. U.; Kale, R. P.; Ghawalkar, A. R.; Nagargoje, D. R.;
Shiradkar, M. R.; Gill, C. H. Bioorg. Med. Chem. Lett. 2008, 18, 6244–6247.
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References and notes
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