Pd-Catalyzed Regioselective Arylation on the C‑5 Position of N‑Aryl 1,2,3-Triazoles

We herein report a highly efficient method for the arylation at the C-5 position of N-aryl 1,2,3-triazoles via a direct palladium catalyzed arylation reaction. The optimal reaction conditions required a combination of Pd­(OAc)2 and tris­(o-tolyl)­phosphine as catalyst, and Cs2CO3 as the base under inert atmosphere. A variety of C-5 substituted N-aryl 1,2,3-triazoles were prepared using these conditions with yields in the 70–88% range. Regioselective C-5 arylations were also performed on 1,4-disubstituted 1,2,3-triazoles. The regioselectivity in triazole substitution at the C-5 position was confirmed by single crystal XRD. In addition, computational investigations of key steps of the catalytic cycle using the density functional theory have provided a rationalization to the selective C-5 arylation of N-aryl 1,2,3-triazoles.