522
D.V. Dekhane et al. / Chinese Chemical Letters 21 (2010) 519–523
Thiols and keto esters failed to give required product which is one of the drawbacks of this methodology.
Surprisingly reaction of ethyl thioglycolate with 2,3-diaminopyridine gave 2-methylimidazopyridine as product
(Table 2, entry 3).
In conclusion we report a unique method for solvent free condensation of esters with arylenediamine using lithium
bromide as catalyst to obtain benzimidazoles and imidazopyridines in good to excellent yields.
General procedure for synthesis of 2-substituted benzimidazoles and imidazopyridines: Arylenediamine (1 mole),
substitued ester (10 mole), LiBr (1 mole) were taken in single neck round bottom flask. Reaction mixture was heated
to 110–115 8C. Progress of the reaction was monitored on TLC. After completion of reaction crude product was
purified by flash chromatography to obtain corresponding 2-substituted benzimidazoles and imidazopyridines
1
compounds these were characterized by H NMR and mass [26].
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