Synthesis of Dendritic ß-Diketones and Their Application in Copper-Catalyzed Diaryl Ether Formation

Phosphorus-based dendrimers decorated with beta-diketones were prepared and fully characterized. These macromolecules, which are the first examples of multivalent dendrimeric beta-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 beta-diketone as the ligand. The proposed conditions are very competitive in terms of catalyst and base loading as the CO coupling can be efficiently performed by using low amounts of copper precursor (1 mol-% instead of 510 mol-%), diketone (4 mol-% instead of 2580 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.