Visible‐Light‐Triggered Quantitative Oxidation of 9,10‐Dihydroanthracene to Anthraquinone by O 2 under Mild Conditions

The development of mild and efficient processes for the selective oxygenation of organic compounds by molecular oxygen (O 2 ) is key for the synthesis of oxygenates. This paper discloses an atom‐efficient synthesis protocol for the photo‐oxygenation of 9,10‐dihydroanthracene (DHA) by O 2 to anthraquinone (AQ), which could achieve quantitative AQ yield (100 %) without any extra catalysts or additives under ambient temperature and pressure. A yield of 86.4 % AQ was obtained even in an air atmosphere. Furthermore, this protocol showed good compatibility for the photo‐oxidation of several other compounds with similar structures to DHA. From a series of control experiments, free‐radical quenching, and electron paramagnetic resonance spin‐trapping results, the photo‐oxygenation of DHA was probably initiated by its photoexcited state DHA*, and the latter could activate O 2 to a superoxide anion radical (O 2 .− ) through the transfer of its electron. Subsequently, this photo‐oxidation was gradually dominated by the oxygenated product AQ as an active photocatalyst obtained from the oxidation of DHA by O 2 .− , and was accelerated with the rapid accumulation of AQ. The present photo‐oxidation protocol is a good example of selective oxygenation based on the photoexcited substrate self‐activated O 2 , which complies well with green chemistry ideals.