Activation of anthraquinone’s electrophilicity by light for a dynamic C-O bond

Coupling of photoswitching with dynamic covalent chemistry enables the control of the formation and cleavage of covalent bonds by light irradiation. Peri-aryloxyanthraquinones feature an exclusive ability to switch electrophilicity by interconversion between para- and ana-quinone isomers, which was used for the first time for implementation of a dynamic C-O bond. Photogenerated ana-isomers undergo a concerted oxa-Michael addition of phenols to give hitherto unknown 4-hydroxy-10,10-diaryloxyanthracen-9-ones. These species were found to be in equilibrium with the corresponding ana-quinones, thus forming a dynamic covalent system of a new type. Withdrawal of the colored ana-quinones from the equilibria by visible-light irradiation resulted in two para-quinones with “locked” aryloxy groups.