Sulfanyl radical addition to alkynyl azides: An insight into vinyl radical cyclization onto the azido function

5-Exo-Cyclization of 2-sulfanylvinyl radicals 16 and 21 is a fast process which prevents intramolecular addition to the sulfanyl aromatic ring and hydrogen abstraction. In contrast, the 2-sulfanylvinyl radicals 3 and 9 are reluctant to add to their aliphatic azido substituent either in a pi-(endo) or in a pi-(exo) mode. These radicals exclusively undergo cyclization onto the adjacent aromatic ring and H-transfer from the thiol present.