Fresh Air Aromatic Hydroxylations

A new palladium-catalyzed reaction brings researchers a step closer to an industrial process that could use air as an oxidizing agent to functionalize inert C–H bonds. Although an efficient, selective, and environmentally benign hydroxylation process is a long-standing goal for organic chemists, such reactions tend to be plagued by low yields or harsh conditions. Now, Yang-Hui Zhang and Jin-Quan Yu of Scripps Research Institute have found a way to hydroxylate C–H bonds on aromatic rings using O₂ or air (J. Am. Chem. Soc., DOI: 10.1021/ja907198n). Their method operates at atmospheric pressure and doesn’t require acidic conditions. It selectively yields ortho-hydroxylated benzoic acids, a motif found in some pharmaceuticals, in moderate to high yields. On the basis of a preliminary study with isotopically labeled reagents, Zhang and Yu suggest that O₂ reacts directly with the aromatic palladium intermediate. “This is the beginning of an exciting new type of synthetically useful C–H oxidation that may have many industrial applications,” says organometallic chemist Jan-Erling Bäckvall of Stockholm University.