Sustainable Microwave-Assisted Routes to N‑Substituted Pyrrolidones Using Natural Deep Eutectic Solvents as Non-innocent Solvents

The current quest for more environmentally friendly processes has stimulated research toward the conversion of biomass into useful chemicals and the replacement of toxic substances. Furthermore, the synergy between environmentally benign enabling technologies and bioderived solvents can boost the sustainability of the conversion processes. In this work, metal-free routes to N-substituted 5-methyl-2-pyrrolidones using natural deep eutectic solvents either as green solvents or as organocatalysts are reported. Different hydrogen donors have been tested for the reductive amination of levulinic acid under dielectric heating: triethoxysilane afforded a series of N-substituted aryl pyrroles in good to excellent yields in only 10 min at 80 °C, while the use of formic acid and ammonium formate required longer times and temperatures (180 °C, 1 h and 30 min, respectively). The described microwave-assisted syntheses represent greener procedures to obtain N-substituted pyrrolidones in good yields while avoiding the use of harsh conditions, toxic organic solvents, and metal catalysts.