Sustainable synthesis of 1,4-disubstituted and N-unsubstituted 1,2,3-triazoles using reusable ZnO-CTAB nanocrystals

Abstract

In this study, a sustainable and eco-friendly copper-free protocol has been developed for the regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles using a zinc-based heterogeneous catalyst. This water-driven procedure links 1,4-disubstituted 1,2,3-triazoles in an azide–alkyne reaction via a one-pot multicomponent pathway without any base or reducing agents and ligands. The sonochemically prepared CTAB-stabilized ZnO particles with a nanorod-like architecture were quite robust and economical as a catalyst and could generate several 1,4-isomeric triazoles by tolerating different substituted azides and alkynes. Moreover, this catalyst was also applied for constructing pharmaceutically active N-unsubstituted 1,2,3-triazoles and 1,4,5-trisubstituted 1,2,3-triazoles with excellent yields. The catalyst was recovered and reused four times to synthesize 1,4-disubstituted and N-unsubstituted 1,2,3-triazoles. In addition, the successful two-gram-scale syntheses also confirm the efficiency of the catalyst. The catalytic protocol was designed considering green chemistry principles, and the eco-friendliness of this methodology was verified by its high eco-score and low E-factor values. This is the first report on using ZnO nanoparticles as a catalyst for regioselective triazole synthesis, and they are far better in terms of catalytic efficiency than many reported zinc-based catalysts.