Highly efficient and diastereoselective gold(I)-catalyzed synthesis of tertiary amines from secondary amines and alkynes: Substrate scope and mechanistic insights

Xin Yuan Liu, Zhen Guo, Sijia S. Dong, Xiao Hua Li, Chi Ming Che

Research output: Contribution to journalArticlepeer-review

37 Scopus citations

Abstract

An efficient method for the synthesis of tertiary amines through a gold(I)-catalyzed tandem reaction of alkynes with secondary amines has been developed. In the presence of ethyl Hantzsch ester and [{(tBu) 2(o-biphenyl)P}AuCl]/AgBF 4 (2 mol %), a variety of secondary amines bearing electron-deficient and electron-rich substituents and a wide range of alkynes, including terminal and internal aryl alkynes, aliphatic alkynes, and electron-deficient alkynes, underwent a tandem reaction to afford the corresponding tertiary amines in up to 99 % yield. For indolines bearing a preexisting chiral center, their reactions with alkynes in the presence of ethyl Hantzsch ester catalyzed by [{(tBu) 2(o-biphenyl)P}AuCl]/AgBF 4 (2 mol %) afforded tertiary amines in excellent yields and with good to excellent diastereoselectivity. All of these organic transformations can be conducted as a one-pot reaction from simple and readily available starting materials without the need of isolation of air/moisture-sensitive enamine intermediates, and under mild reaction conditions (mostly room temperature and mild reducing agents). Mechanistic studies by NMR spectroscopy, ESI-MS, isotope labeling studies, and DFT calculations on this gold(I)-catalyzed tandem reaction reveal that the first step involving a monomeric cationic gold(I)-alkyne intermediate is more likely than a gold(I)-amine intermediate, a three-coordinate gold(I) intermediate, or a dinuclear gold(I)-alkyne intermediate. These studies also support the proposed reaction pathway, which involves a gold(I)-coordinated enamine complex as a key intermediate for the subsequent transfer hydrogenation with a hydride source, and reveal the intrinsic stereospecific nature of these transformations observed in the experiments. Producing tertiary amines: The Au I-catalyzed tandem reaction of alkynes with secondary amines provides simple and efficient access to highly substituted tertiary amines with excellent yields and good to excellent diastereoselectivity. Mechanistic studies confirm that a possible reaction pathway involves intermolecular hydroamination via a monomeric cationic gold(I)-alkyne intermediate and subsequent transfer hydrogenation via a gold(I)-coordinated enamine intermediate.

Original languageEnglish (US)
Pages (from-to)12932-12945
Number of pages14
JournalChemistry - A European Journal
Volume17
Issue number46
DOIs
StatePublished - Nov 11 2011

Keywords

  • alkynes
  • density functional calculations
  • diastereoselectivity
  • gold
  • tertiary amines

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