Excited-state intramolecular proton transfer (ESIPT) based emitters have attracted increasing attention due to their broad application in fluorophore imaging, chemical sensing and optoelectronic devices. Such luminophores exhibit unique properties containing a large Stokes shift of up to 12000 cm-1 without the tendency of self-reabsorption or dual emission behavior. Typical synthetic methods for the incorporation of the crucial hydrogen donating phenols are based on transition metal-catalyzed C−H hydroxylations and require elevated temperatures as well as non-sustainable oxidants (e.g. hypervalent iodine reagents or peroxides). Direct C−H hydroxylations via deprotonative metalations are very rare and again based on peroxides as oxygen donors. Applying either molecular oxygen or air usually results in low yields and incomplete conversion of metalated arenes. Herein, we present the direct hydroxylation of 2-aryloxazolines via a direct deprotonative metalation and oxidation using molecular oxygen or air as green oxidants. This method proceeds under mild conditions at room temperature and perfect ortho selectivity. The resulting phenols exhibit tunable luminescence properties, induced by ESIPT, and hence this method opens new opportunities for the sustainable synthesis of luminescent organic molecules. Besides a detailed discussion about the synthetic method itself, including the underlying reaction mechanism, the luminescent properties of selected phenols will be deeply discussed.

Aerobic C(sp2)−H hydroxylations of 2-aryloxazolines: Fast access to novel ESIPT-based luminophores

2019 Fall National Meeting

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