Synthesis of Benzimidazoles from Amino Acids with Solvent-free Melting Method

By using low cost and readily available amino acids as the synthetic blocks, a series of 2-aminomethyl-benzimidazole are synthesized with solvent-free melting method. While the condensation of aspartic acid (or asparagine) with o-diaminobenzene gives the fluorescent bisbenzimidazole product without amino group via the further deamination reaction in the melting reaction system. The condensation reactions between most amino acids and o-diaminobenzenes exhibits higher yields of 58 to 86 % (mostly over 66 %), shorter reaction time (5 h) than that previously reported and better tolerance for different functional groups in amino acids. The structures of twenty benzimidazoles with multifunctional groups, including thirteen new compounds, are systematically characterized with FTIR, H-1 NMR, C-13 NMR, MS and elemental analysis. These investigations are beneficial to the further researches on their applications in biochemistry, coordination chemistry and organic synthesis intermediates.