Palladium-Catalyzed Direct Diarylation of 2-Benzyl-1,2,3-triazole: a Simple Access to 4-Aryl- or 4,5-Diaryl-2-benzyl-1,2,3-triazoles and Phenanthro[9,10-d][1,2,3]triazoles

The reactivity of 2-benzyl-1,2,3-triazole in palladium-catalyzed direct arylation was studied. The reaction conditions for the selective synthesis of 2-benzyl-4-aryl-1,2,3-triazoles in moderate to high yields using phosphine-free Pd(OAc)(2) catalyst and inexpensive KOAc base have been found. Then, from these 4-aryl-1,2,3-triazoles, the palladium-catalyzed C-H bond functionalization of the C5-position allowed the synthesis of the corresponding 4,5-diarylated 2-benzyl-1,2,3-triazoles. This selective 4,5-diarylation of 2-benzyl-1,2,3-triazole was successfully applied for the straightforward building of the pi-extended polycyclic heteroaromatic structures phenanthro[9,10-d][1,2,3]triazoles through Pd-catalyzed C4- and C5-intermolecular arylations followed by Pd-catalyzed C-H intramolecular arylation.