Direct Synthesis of 4-Aryl-1,2,3-triazoles via I2-Promoted Cyclization under Metal- and Azide-Free Conditions.

We herein report an iodine-mediated formal [2 + 2 + 1] cyclization of methyl ketones, p-toluenesulfonyl hydrazines, and 1-aminopyridinium iodide for preparation of 4-aryl-NH-1,2,3-triazoles under metal- and azide-free conditions. Notably, this is achieved using p-toluenesulfonyl hydrazines and 1-aminopyridinium iodide as azide surrogates, providing a novel route toNH-1,2,3-triazoles. Furthermore, this approach provides rapid and practical access to potent inhibitors of indoleamine 2,3-dioxygenase (IDO).