Metal- and Additive-Free Aerobic Dehydrogenation of N-Heterocycles and Hydrocarbons by N-Doped Carbon

Over metal catalysts, N-heteroarenes, as one of the most versatile building blocks in pharmaceuticals, bioactive molecules and natural products, can be easily accessed by the oxidation of N-heterocycles. Herein, we describe N-doped hierarchical pore carbons (N-HPCs) derived from readily available biomass (flour) efficiently catalyzed aerobic dehydrogenation of N-heterocycles without any additives under mild conditions, owing to N dopant and high surface area indicated by characterization analysis. A wide range of N-heteroarenes including quinolines, quinolinol, dihydroisoquinolines, isoquinolines, indoles, quinoxaline and acridine were obtained in good to excellent yields (36 examples, up to 99% yield). Mechanistic studies revealed a strikingly different non-free radical process from metal catalysts, for which an apparent activation energy of 66.4 kJ mol(-1) was found. Moreover, the N-doped carbon exhibited robust stability and yielded 74.5% quinoline at the sixth reaction. The use of metal-free catalysts in organic synthesis is attractive but practically challenging. This work provides a promising example for metal-free catalysis.