DFT studies on the mechanism of Ag2CO3-catalyzed hydroazidation of unactivated terminal alkynes with TMS-N3: An insight into the silver(I) activation mode

5 years ago

DFT studies on the mechanism of Ag2CO3-catalyzed hydroazidation of unactivated terminal alkynes with TMS-N3: An insight into the silver(I) activation mode

Jingping Zhang, Pin Xiao, Haiyan Yuan, Yiying Zheng

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-N3 participated hydroazidation proceed through HN3 formation, deprotonation and silver acetylides formation, nucleophilic addition, and protonation of terminal carbon by AgHCO3. It is also found that water molecules and activation modes of Ag (I) have a significant influence on the title reaction mechanism. Initially, catalyst Ag2CO3 coordinates preferentially with internal N atom of TMS–N3 to assist water as hydrogen source and proton-shuttle in facilitating HN3 formation. Then, the regioselective anti-addition of HN3 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, Ag2CO3 is the critical catalyst, acting as activator, base, and stabilizer to promote the HN3 and vinyl azide formation. Water molecule plays an important role as proton shuttle to promote HN3 and key active silver acetylides formation, thus improving the yield of product. © 2017 Wiley Periodicals, Inc. DFT calculations were conducted to disclose the mechanism, regioselectivity, and activation mode of silver (I) in Ag2CO3-catalyzed 2-azidoallyl alcohols of ethynyl carbinols and TMS–N3. It is found that water molecules and activation modes of Ag (I) have a significant influence on this transformation. Furthermore, the π-silver activation and silver σ-activation mode is dominate in the formation of HN3 and the vinyl azide, recpectively.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/jcc.24879