Photocatalytic Oxidative Bromination of Electron-Rich Arenes and Heteroarenes by Anthraquinone

The estimated excited oxidation potential of sodium anthraquinone-2-sulfonate (SAS) increases from 1.8 V to about 2.3 V vs SCE by protonation with Bronsted acids. This increased photooxidation power of protonated anthraquinone was used for the regio-selective oxidative bromination of electron rich (hetero) arenes and drugs in good yield. The mild reaction conditions are compatible with many functional groups, such as double and triple bonds, ketones, amides and amines, hydroxyl groups, carboxylic acids and carbamates. Mechanistic investigations indicate the photooxidation of the arene followed by nucleophilic bromide addition as the likely pathway.