Cobalt single-atom catalysts for domino reductive amination and amidation of levulinic acid and related molecules to N-heterocycles

Abstract

The development of single-atom-based catalysts (SACs), which bridge the traditional areas of homogeneous and heterogeneous catalysis, continues to be important for achieving organic synthesis in a more efficient and practical manner. Here, we report reusable cobalt-based SACs for the selective and general reductive amination of levulinic acid and related keto acids, which is of interest in the context of valorization of biomass. The optimal Co-SAC-based catalyst is prepared by pyrolysis (800°C) of cobalt-phenanthroline complexe on carbon and subsequent acid treatment. The resulting Co-SACs showed amazing activity compared with the corresponding Co-nanoparticles and displayed an excellent substrate scope for various reductive domino transformations including reactions of levulinic acid with nitro compounds and nitriles to produce various N-substituted pyrrolidones in good to excellent yields. Further, the synthesis of diverse isoindolinones from aromatic ketoacids and amines/nitro compounds was performed with the optimal catalyst system. • Preparation of stable and reusable Co-SACs catalysts • Reductive amination and amidation of levulinic acid and related molecules • Synthesis of >90 functionalized and structurally diverse N-heterocycles • Applicable for the preparation of bioactive molecules The effective catalytic conversion of biomass-based feedstocks to produce bulk and fine chemicals is a major goal of current chemical research. In this respect, specifically reductive aminations and amidations are interesting, too. To improve the sustainability of such processes, inexpensive, earth-abundant base metals should be employed as catalysts to replace precious metals that currently dominate in this field. Here, we show that cobalt catalysts with isolated metal sites (SACs) enable efficient domino reductive amination and amidation of levulinic acid and related molecules to give a wide array of N-heterocycles. We anticipate that these Co-catalytic systems will create more opportunities for the conversion of biomass-based feedstocks to many value-added compounds. The effective conversion of renewable resources, especially biomass-based feedstocks, to produce chemicals, fuels, and energy is of central importance. To valorize these feedstocks, the development of suitable catalysts, especially single-atom catalysts (SACs), which bridge traditional homogeneous and heterogeneous catalysis, is highly desired. In this respect, we developed Co-based SACs, which allow for the domino reductive amination and amidation of levulinic acid and related molecules to produce functionalized and structurally diverse N-heterocycles including bioactive molecules.