Abstract
A small library of benzimidazoles with a range of side-chain substituents have been synthesized through the condensation reaction of o-phenylenediamine derivatives and several other commercially available materials. The reactions were catalyzed by either 4M HCl or 1,3-dibromo-5,5-dimethylhydantoin (DBDMH). The compounds synthesized using DBDMH as the catalyst required a shorter reaction time, the yield was higher and the workup procedure was not as tedious as those produced using 4M HCl as the catalyst. The structural elucidations of synthesized compounds have been confirmed through spectroscopic analysis. 13C NMR analysis of some of the synthesized compounds showed that the appearance of carbon signals in the NMR spectrum is affected by the nature of the NMR solvent and temperature.The exchange-induced broadening of the 13C NMR signal was probably facilitated by the intermolecular proton exchange between the NH of the benzimidazole and the H2O present in the DMSO-d6 solvent. Key words: 1,3-dibromo-5,5-dimethylhydantoin, benzimidazole, solvent-effect, structure elucidation, synthetic method.
Highlights
Benzimidazoles have occupied a prominent place in medicinal chemistry due to their significant effect as therapeutics in clinical applications
After the completion of the reaction which was monitored by Thin layer chromatography (TLC), the crude product precipitated on Scheme 1
The melting point and spectroscopic data for 7 could not be found in the Scifinder® and Reaxys® database; these data is included in the experimental section of this report. 1H NMR analysis of 8 and 9, the signals displayed by the aromatic protons showed patterns different from those observed in previously synthesized compounds; especially a doublet of doublet of doublet signal which is probably due to the strong coupling between hydrogen and fluorine
Summary
Benzimidazoles have occupied a prominent place in medicinal chemistry due to their significant effect as therapeutics in clinical applications. In a bid to improve yields and reaction conditions, it is conceivable to develop a series of benzimidazole derivatives using 1,3-dibromo-5,5-dimethylhydantoin (DBDMH) as an efficient homogeneous catalyst and carry out a comparison with the conventional Phillip’s synthesis. General method for the conventional synthesis of benzimidazole derivatives
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