Phenols Set The Stage For Greener Cross-Couplings

Palladium-catalyzed amination of aryl halides to form aryl amines is a leading example of a cross-coupling reaction, one of the most important transformations in organic synthesis. The aryl amine products are common building blocks for preparing pharmaceutical compounds, dyes, and electronic materials. However, the aryl halide starting reagents must be presynthesized from petroleum-based feedstocks, which adds reaction steps to a synthesis and leads to unwanted halide waste. Zhengwang Chen, Huiying Zeng, Chao-Jun Li, and coworkers at McGill University have developed a green alternative by using phenols, which can be derived from the biobased material lignin, instead of aryl halides (Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201506751). Chemists have already developed methods to convert phenols to aryl amines, but the approaches require first converting the phenols into aryl sulfonates, esters, or other intermediates. The new McGill synthesis, which builds on the team’s work to convert phenols to cyclohexylamines, offers a direct coupling of phenols with an amine or with anilines via a tandem reduction-condensation-dehydrogenation process. The researchers used the method to convert phenols to secondary and tertiary aryl amines, as well as the diol catechol to a diamine and to a nitrogen heterocycle.