Aromatic N-heterocycles are found, e.g., in pharmaceutically active molecules and natural products. They can be synthesized, for example, via aerobic oxidative aromatizations. This type of reaction is usually catalyzed by homogeneous catalysts, which can be difficult to recover and recycle. While there are some examples of heterogeneous catalysts used for this application, they are hampered by limited substrate scopes and a need for expensive metals.

Dong Gu, Wuhan University, China, and colleagues have developed a heterogeneous catalytic strategy using a mesoporous cobalt oxide for the aerobic oxidative aromatization of N‐heterocycles. The team synthesized mesoporous Co₃O₄ from Co(NO₃)₂·6 H₂O via a nanocasting method using the mesoporous silica SBA-15 as a hard template, followed by calcination. The silica template was removed with an NaOH solution.

The resulting catalyst was used to convert 1,2,3,4-tetrahydroquinoline derivatives (THQs, used as model substrates) to the corresponding parent quinolines. The reactions were performed in dimethyl sulfoxide (DMSO) at 140 °C under an air atmosphere. The desired products were obtained in moderate to good yields. The catalyst can be easily recovered and reused at least six times, and the reaction can be performed on a gram scale.

• Highly Ordered Mesoporous Cobalt Oxide as Heterogeneous Catalyst for Aerobic Oxidative Aromatization of N‐Heterocycles,
  Dong Gu, Yue Cao, Yong Wu, Yuanteng Zhang, Jing Zhou, Wei Xiao,
  ChemCatChem 2021.
  https://doi.org/10.1002/cctc.202100644