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.