Abstract
Recently, great attention has been paid to environmentally friendly oxidations, especially those using organocatalysts and hydrogen peroxide or oxygen as terminal oxidants. The development of such systems is directed to sulfoxidations, Baeyer-Villiger oxidations and epoxidations which are the key transformations in organic synthesis.
New target on this field is oxidation of arylboronic acid to corresponding phenols representing useful alternative to usually used transformation of diazonium salts. However, methods of arylboronic acids oxidations are still limited to oxidations by stoichiometric agents or procedures catalyzed by metal containing catalysts.
Here, we present oxidation of arylboronic acids to appropriate phenols catalyzed by flavinium salts 1 or 2. This reaction proceeds by mechanism analogical to oxidations mediated by flavin cofactors in flavoenzymes, i.e with oxygen as stoichiometric agent, in the presents of reducing agent producing reduced flavin and under mild conditions.
Various solvents and reducing agents were tested to optimize reaction conditions.