Synthesis and NMR Analysis of 1,4-Disubstituted 1,2,3-Triazoles Tethered to Pyridine, Pyrimidine, and Pyrazine Rings

A combinatorial modular approach based on the click copper(I)-catalysed azide-alkyne cycloaddition reaction was used to prepare a library of selected 1,4-disubstituted 1,2,3-triazoles differently functionalized with heteroaryl groups including pyridine, pyrimidine, and pyrazine. Three different copper(I) sources, i.e., CuSO4/sodium ascorbate, CuBr(PPh3)(3), and (CuOTf)(2)center dot C6H6 were used to promote the coupling reactions of a range of aryl, heteroaryl, and heteroarylmethyl azides with alkyne click partners. As the target heteroaryl triazoles were designed to serve as advanced ligands or ligand precursors for metal coordination, they were fully characterized by H-1, C-13, and N-15 NMR spectroscopy. The resonances were assigned on the basis of 1D and 2D NMR experiments. H-1-N-15 gs-HMBC was used as a practical tool to determine N-15 NMR chemical shifts at the natural abundance level of the N-15 isotope.