Oxidized active carbon (oAC) catalyses the formation of polysubstituted quinolines from o‐vinyl anilines and aldehydes. The reaction proceeds in a cascade manner through condensation, electrocyclization and dehydrogenation, and gives access to a wide range of quinolines with alkyl and/or aryl substituents as demonstrated with 40 examples. The metal‐free catalytic procedure allows a heterogeneous protocol for the synthesis of various polysubstituted quinolines. The mechanistic studies imply that both the acid and quinoidic groups in oAC are integral for the catalytic manifold.

Visible-light-excited 9,10-phenanthrenequinone (PQ*) was used as a photocatalyst for the synthesis of polysubstituted quinolines via the electrocyclization of 2-vinylarylimines. Up to quantitative yields of 2,4-disubstituted quinolines were received after 1 h of excitation with blue LEDs at room temperature when MgCO 3 was used as an additive in DCM. On the basis of experimental and DFT studies, we propose that PQ* induces one-electron oxidation of the imine substrate that triggers the electrocyclization mechanism.

In 2000, Fukuzumi and co‐workers reported a seminal study on the photochemical oxidation of benzylic alcohols with visible‐light‐excited 9,10‐phenanthrenequinone (PQ) under argon atmosphere (J. Am. Chem. Soc. 2000, 122, 8435). We optimized the reaction conditions they reported and were able to oxidize 1‐(4‐methoxyphenyl)ethanol quantitatively to 4'‐methoxyacetophenone in only 15 min with 10 mol % PQ as a photocatalyst under oxygen. However, we observed a significant decrease in the oxidation rate with more electron‐deficient benzylic alcohols as starting materials. To improve the photooxidation performance, we designed a high‐yielding synthetic route for a novel, more electron‐deficient PQ derivative, 3,6‐bis(trifluoromethyl)‐9,10‐phenanthrenequinone (PQ‐CF3). Its efficiency as a photocatalyst in the fast oxidation of secondary alcohols was demonstrated not only with several electronically diverse benzylic alcohols but also with aliphatic substrates. The comprehensive mechanistic studies based on Hammett plot construction, kinetic isotope experiments, and DFT computations suggest that the mechanistic pathway of the alcohol oxidation is dependent on the electronic properties of both the catalyst and the substrate. As the key mechanistic discovery, we showed that the newly developed PQ‐CF3 operates as a highly efficient hydrogen atom transfer (HAT) catalyst.