Aerobic Oxidative Hydroxylation of Arylboronic Acids under Visible-Light Irradiation without Metal Catalysts or Additives

Phenols are versatile synthetic intermediates and key structural motifs in many natural products and biologically active compounds. We herein report a visible-light-induced aerobic oxidative hydroxylation of arylboronic acids/pinacol esters using air as oxidant and without using any catalysts and base, etc., additives, providing a green entry to a variety of phenols in a highly efficient and concise fashion. This novel reaction is enabled by photoactivation of an electron donor-acceptor complex, in which THF serves as both the solvent and electron donor. DFT studies indicated that the oxidation process involves a concerted hydrogen abstraction transfer from THF and dehydroxylation of boronic acid undergoing spin crossover from triplet to singlet to produce an active peroxoboronic acid intermidiate. Salient merits of this chemistry include broad substrate scope and excellent functional group tolerance, gram-scale synthesis, and versatile late-stage functionalizations as well as the use of air, visible light, and catalyst- and additive-free conditions. This strategy introduces a novel photoreaction mode with the aid of a solvent, offering a succinct and environmentally sustainable route for synthesizing phenols. The strong practicability and highly efficient access to modifying complex biorelevant molecules bode well for the potential applications of this chemistry in pharmaceutical chemistry.

Oxidative Cleavage of Csp3-Csp2 and Csp3-H Bonds with KOtBu: Highly Robust and Practical Synthesis of Diaryl/(het-Ar) Ketones

Herein, we report an efficient and practical approach for synthesizing diaryl(het) ketones from R-CO-CHR-Ar through a simultaneous oxidative cleavage of C-C and C-H bonds using KO^tBu. This method enables synthesizing a variety of unsymmetrical and symmetrical (hetero)aryl ketones in excellent yields, which are otherwise difficult to make. Besides, we synthesized natural products using this method.

A scalable and green one-minute synthesis of substituted phenols

A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H₂O₂/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.