Metal-Free Cascade [4 + 1] Cyclization Access to 4-Aryl--1,2,3-triazoles from -Tosylhydrazones and Sodium Azide

A molecular iodine-mediated coupling cyclization reaction for the synthesis of 4-aryl--1,2,3-triazoles has been developed from -tosylhydrazones and sodium azide. This metal-free cascade [4 + 1] cyclization reaction could rapidly synthesize valuable compounds via a sequential C-N and N-N bond formation. Mechanistic studies demostrate that the nitrogen atoms of the 1,2,3-triazoles are not entirely from sodium azide.