Highly Efficient [3 + 2] Cycloaddition: Click Synthesis of Novel 1H-indol-3-yl-benzo[d]imidazole Bis-triazoles

A series of novel 1-((1H-1,2,3-triazol-4-yl)methyl)-2-(1-((1H-1,2,3-triazol-4-yl)methyl)-5-substituted-1H-indol-3-yl)-6-substituted-1H-benzo[d]imidazoles 5a–i have been prepared using click chemistry as an ideal strategy where [3 + 2] cycloaddition of azides with terminal alkynes has been developed as the target compounds. In route-II, 5-substituted-1H-indole-3-carbaldehydes 1a–c react with 5-substituted orthophenylenediamine 8 to give desired products, that is, 6-substituted-2-(5-substituted-1H-indol-3-yl)-1H-benzo[d]imidazole 6a–i. Here, 6a–i react with 2 equiv of propargylbromide 7 to give novel 6-substituted 2-(5-substituted-1-(prop-2-yn-1-yl)-1H-indol-3-yl)-1-(prop-2-yn-1-yl)-1H-benzo[d]imidazole 4a–i. 4a–i were reacted with 2 equiv of NaN₃ in t-butanol/water (1:2) and add catalytic amount of CuSO₄.5H₂O. Stir the reaction mixture at room temperature to get the target products 5a–i. Here, obtained products contain four rings, that is, one indole, two triazoles, and one benzimidazole. The main advantages of this method are short reaction times, easy workup, higher yields (88–92%), and no by-products formation.