Visible Light-directly Triggered Quantitative Oxidation of 9,10-dihydroanthracene to Anthraquinone by Molecular Oxygen under Normal Temperature and Pressure.

The development of mild and efficient process for the selective oxygenation of organic compounds by molecular oxygen (O 2 ) can be one of the key technologies for synthesizing 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 can achieve quantitative AQ yield (100%) without any extra catalysts and additives under normal temperature and pressure. Also, 86.4% AQ yield is obtained even in air atmosphere. Furthermore, this protocol has a good compatibility for the photo-oxidation of several other compounds with a similar structure to DHA. Based on a series of control experiments and free radical quenching and EPR spin trapping results. The photo-oxygenation of DHA is likely initiated by its photo-excited state DHA* and the latter can activate O 2 to a superoxide anion radical (O 2 ⚫- ) via a transfer of its electron. Subsequently, this photo-oxidation is gradually dominated by the oxygenated product AQ as an active photo-catalyst, obtained from the oxidation of DHA by O 2 ⚫- , and it is accelerated with the rapid accumulation of AQ. The present photo-oxidation protocol gives a good example for the selective oxygenation based on the photo-excited substrate self-activated O 2 , which compliances well with 'green' chemistry ideals.