Heterogeneous metal catalysts constitute a very important tool for the synthesis of functional materials and fine chemicals owing to their high efficiency, robustness, and facile recyclability. Biaryls are privileged structural motifs in many natural products, chiral ligands, and catalysts. The oxidative biaryl coupling reaction is one of the most promising methods for biaryl synthesis in terms of atom and step economies. However, although oxidative biaryl coupling of naphthols has been studied thoroughly, the coupling of aryl amines providing biaryl amines like 2,2'-diamino-1,1'-binaphthyl (BINAM) and 2-amino-2'-hydroxy-1,1'-binaphthyl (NOBIN) derivatives remains elusive. Recently, we have found that aryl amines are efficiently dimerized with the use of a heterogeneous Rh/C catalyst under acidic conditions. This heterogeneously catalyzed method can be adapted to the highly selective cross-coupling reaction of aryl amines and the intramolecular biaryl coupling reaction. Furthermore, we developed an aerobic direct C-H oxidation of polycyclic aromatics catalyzed by a recyclable heterogeneous rhodium catalyst. These methodologies are advantageous compared with the existing reactions owing to the mild aerobic conditions employed and the facile recyclability of the heterogeneous catalysts used.
Keywords: acyloxylation; aerobic oxidation; aryl amine; biaryl; heterogeneous catalyst; oxidative coupling.