DFT studies on the mechanism of Ag CO -catalyzed hydroazidation of unactivated terminal alkynes with TMS-N : An insight into the silver(I) activation mode.

Silver-mediated hydroazidation of unactivated alkynes has been developed as a new method for the synthesis of vinyl azides. Density functional theory calculations toward this reaction reveal that terminal alkynes with TMS-N participated hydroazidation proceed through HN formation, deprotonation and silver acetylides formation, nucleophilic addition, and protonation of terminal carbon by AgHCO . It is also found that water molecules and activation modes of Ag (I) have a significant influence on the title reaction mechanism. Initially, catalyst Ag CO coordinates preferentially with internal N atom of TMS-N to assist water as hydrogen source and proton-shuttle in facilitating HN formation. Then, the regioselective anti-addition of HN to triple bond of active silver-acetylide or ethynyl carbinols affords product vinyl azide via Ag-C σ-bond activation or Ag…C π-coordination activation modes, and the former one is more favorable. The origin of the difference regioselectivity is ascribed to the electronic and orbital effects of the reactive sites. Moreover, Ag CO is the critical catalyst, acting as activator, base, and stabilizer to promote the HN and vinyl azide formation. Water molecule plays an important role as proton shuttle to promote HN and key active silver acetylides formation, thus improving the yield of product. © 2017 Wiley Periodicals, Inc.