Synthesis of Dendritic β-Diketones and Their Application in Copper-Catalyzed Diaryl Ether Formation
Résumé
Phosphorus-based dendrimers decorated with β-diketones were prepared and fully characterized. These macromolecules, which are the first examples of multivalent dendrimeric β-diketones, were tested as ligands for copper in O-arylations of 3,5-dimethylphenol by aryl bromides. Although no dendrimer effect was observed, we were able to highlight a very efficient catalytic system that involved a monomeric β-diketone as the ligand. The proposed conditions are very competitive in terms of catalyst and base loading as the C-O coupling can be efficiently performed by using low amounts of copper precursor (1 mol-% instead of 5-10 mol-%), diketone (4 mol-% instead of 25-80 mol-%), and base (1.2 equiv. of cesium carbonate instead of 2 or more). Moreover, the absence of the dendrimer effect is explained by the decomposition of the dendrimer under the reaction conditions, which led to the release of the peripheral diketone moieties.