Mechanistic Insight into the Gold-Catalyzed Carboxylative
Cyclization of Propargylamines
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Abstract
DFT
calculations have been carried out to study the detailed mechanisms
for the carboxylative cyclization of propargylamine using CO<sub>2</sub> catalyzed by NHC-gold(I) complexes. The calculation results indicate
that the reaction starts with an N-coordinated species, [(NHC)Au(propargylamine)]Cl,
which undergoes isomerization to an alkyne-coordinated species. An
amine–carbon dioxide interaction gives a carbamate ion species,
from which a nucleophilic attack of the in-plane lone pair of electrons
in the carbamate anion moiety on one of two coordinated alkyne carbons
leads to formation of a five-membered-ring intermediate. The final
product is generated through deprotonation and protonation processes.
Through a detailed mechanistic study, we found that the substrate
propargylamine assists (catalyzes) the deprotonation and protonation
processes. Careful study of the solvent effect indicates that solvents,
which are polar and capable of hydrogen bonding, promote the catalytic
reactions through stabilizing the carbamate ion intermediate species