1,3-Dipolar Cycloaddition of Alkanone Enolates with Azides in Deep Eutectic Solvents for the Metal-Free Regioselective Synthesis of Densely Functionalized 1,2,3-Triazoles

An eco-friendly metal-free protocol was developed for the regioselective synthesis of densely functionalized 1,2,3-triazoles through a 1,3-dipolar cycloaddition reaction of alkanone enolates with azides performed in the environmentally responsible choline chloride/urea or choline acetate/urea eutectic mixture. This approach displays a broad substrate scope, straightforwardly furnishing the desired triazoles (including the challenging phenolic derivatives) in yields of up to 98 %, while working at room temperature and under aerobic conditions. The practicability of the method is exemplified by the sustainable synthesis of some pharmaceutically relevant triazole derivatives carried out via telescoped, one-pot cycloaddition/reduction processes in the same eutectic mixture without any halfway isolation/purification step of intermediates.