AgN₃-Catalyzed Hydroazidation of Terminal Alkynes and Mechanistic Studies

The hydroazidation of alkynes is the most straightforward way to access vinyl azides-versatile building blocks in organic synthesis. We previously realized such a fundamental reaction of terminal alkynes using Ag₂CO₃ as a catalyst. However, the high catalyst loading seriously limits its practicality, and moreover, the exact reaction mechanism remains unclear. Here, on the basis of X-ray diffraction studies on the conversion of silver salts, we report the identification of AgN₃ as the real catalytic species in this reaction and developed a AgN₃-catalyzed hydroazidation of terminal alkynes. AgN₃ proved to be a highly robust catalyst, as the loading of AgN₃ could be as low as 5 mol %, and such a small proportion of AgN₃ is still highly efficient even at a 50 mmol reaction scale. Further, the combination of experimental investigations and theoretical calculations disclosed that the concerted addition mechanism via a six-membered transition state is more favored than the classical silver acetylide mechanism.