Functionalization of N-H Linkage at Benzimidazole for the Construction of 1,3,4-Oxadiazole Derivatives

Benzimidazole is a bicyclic heterocyclic aromatic compound that contains a combination of a six-membered ring and a five-membered ring with two nitrogen atoms. The current study aims to combine these two moieties to identify new benzimidazole-based 1,3,4-oxadiazole derivatives. In this work, the preparation of new benzimidazole-containing substituted 1,3,4-oxadiazoles 3-16 has been described using a five-step process. The SN2 displacement reaction between benzimidazole and bromoacetic acid afforded the corresponding acid 1 in an 87% yield. Product 1 was treated with thionyl chloride to furnish the desired acid chloride form of 1. The next step involved the nucleophilic addition of hydrazine hydrate (99%) to the acid chloride derivative, yielding 91% of hydrazide 2. The aldimines derived from hydrazide 2 were obtained by treating compound 2 with different aromatic aldehydes, which were then used to access the desired products (3-16) via an oxidative cyclization reaction. This was achieved through treatment with I2/K2CO3 in dimethyl sulfoxide. The target compounds (3-16) were synthesized in yields ranging from 50% to 88%. The structures of the synthesized products were characterized using FT-IR and 1H NMR spectroscopy for some of them