RESUMEN
The oxidation of phenols is the subject of extensive investigation, but there are few catalytic aerobic examples that are chemo- and regioselective. Here we describe conditions for the ortho-oxygenation or oxidative coupling of phenols under copper (Cu)-catalyzed aerobic conditions that give rise to ortho-quinones, biphenols or benzoxepines. We demonstrate that each product class can be accessed selectively by the appropriate choice of Cu(I) salt, amine ligand, desiccant and reaction temperature. In addition, we evaluate the effects of substituents on the phenol and demonstrate their influence on selectivity between ortho-oxygenation and oxidative coupling pathways. These results create an important precedent of catalyst control in the catalytic aerobic oxidation of phenols and set the stage for future development of catalytic systems and mechanistic investigations.
Asunto(s)
Oxígeno/química , Fenoles/química , Polímeros/química , Aerobiosis , Estructura Molecular , Oxidación-ReducciónRESUMEN
The importance of aromatic C-O, C-N, and C-S bonds necessitates increasingly efficient strategies for their formation. Herein, we report a biomimetic approach that converts phenolic C-H bonds into C-O, C-N, and C-S bonds at the sole expense of reducing dioxygen (O2) to water (H2O). Our method hinges on a regio- and chemoselective copper-catalyzed aerobic oxygenation to provide ortho-quinones. ortho-Quinones are versatile intermediates, whose direct catalytic aerobic synthesis from phenols enables a mild and efficient means of synthesizing polyfunctional aromatic rings.
Asunto(s)
Fenoles/química , Biomimética , Catálisis , Oxidación-ReducciónRESUMEN
Straight to the point: The direct 3- or 4-arylation of pyrrole derivatives through C--H bond activation proceeds in moderate to good yields using Pd(OAc)(2) as catalyst. In contrast to classical coupling procedures, the preparation of an organometallic derivative is not required and the major by-products are AcOH/KBr instead of metallic salts.