Flow chemistry as a versatile tool for the synthesis of triazoles
Continuous-flow processing offers unprecedented opportunities to accelerate, integrate, simplify, scale-up and automatize chemical reactions, in combination with an inherently safer and ‘greener’ nature over traditional batch-based syntheses. Triazoles are amongst the most important and most intensively studied heterocycles due to their diverse biological activities and incredible number of applications in labeling, modification and synthesis of various biomolecules, polymers and supramolecular assemblies. Many research groups have demonstrated that both copper-catalyzed and catalyst-free cycloadditions between azides and various dipolarophiles leading to triazoles or triazole-based structures can be greatly facilitated through the beneficial features of continuous-flow processing. The present review therefore surveys the flow chemistry-based approaches for the synthesis of triazoles, covering the most important catalytic and catalyst-free strategies in continuously operated systems published during the past decade.