We report a system with ethylene-bridged flavinium salt 2b which catalyzes the aerobic oxidation of toluenes and benzyl alcohols with high oxidation potential (E ox > +2.5 V vs SCE) to give the corresponding benzoic acids under visible light irradiation. This is caused by the high oxidizing power of excited 2b (E(2b*) = +2.67 V vs SCE) involved in photooxidation and by the accompanying dark organocatalytic oxygenation provided by the in situ formed flavin hydroperoxide 2b-OOH.

7,8‐Dimethoxy‐3‐methyl‐1,10‐ethylenealloxazinium chloride (1a) was found to be a superior photooxidation catalyst among substituted ethylene‐bridged flavinium salts (R=7,8‐diMeO, 7,8‐OCH2O‐, 7,8‐diMe, H, 7,8‐diCl, 7‐CF3 and 8‐CF3). Selection was carried out based on structure vs catalytic activity and properties relationship investigations. Flavinium salt 1a proved to be robust enough for practical applications in benzylic oxidations/oxygenations, which was demonstrated using a series of substrates with high oxidation potential, i. e., 1‐phenylethanol, ethylbenzene, diphenylmethane and diphenylmethanol derivatives substituted with electron‐withdrawing groups (Cl or CF3). The unique capabilities of 1a can be attributed to its high photostability and participation via a relatively long‐lived singlet excited state, which was confirmed using spectroscopic studies, electrochemical measurements and TD‐DFT calculations. This allows the maximum use of the oxidation power of 1a, which is given by its singlet excited state reduction potential of +2.4 V. 7,8‐Dichloro‐3‐methyl‐1,10‐ethylenealloxazinium chloride (1 h) can be used as an alternative photocatalyst for even more difficult substrates.

The front cover picture, prepared by Dr D. Prukala, illustrates ethylene‐bridged 7,8‐dimethoxyflavinium salt excited with blue light. This salt is characterised by relatively long‐lived excited state and high photostability thus making it superior among flavin photocatalysts for aerobic oxidations/oxygenations. The flavinium salt was demonstrated to provide photooxidation of various benzylic substrates, even those with high oxidation potential (X=Cl, CF3). Details can be found in the Research Article by Sikorski, Cibulka and co‐workers. (A. Pokluda, Z. Anwar, V. Boguschová, I. Anusiewicz, P. Skurski, M. Sikorski, R. Cibulka, Adv. Synth. Catal. 2021, 363, 4371–4379; DOI: 10.1002/adsc.202100024)