Theoretical study on the mechanism of N-heterocyclic carbene catalyzed transesterification reactions

The mechanism of N-heterocyclic carbene (NHC) catalyzed transesterification reactions have been studied using density functional theory. Our study shows that the role of NHC is to assist proton transfer from alcohol to the carbonyl oxygen, forming the tetrahedral intermediate, which then decomposes to the acylated product. Our predicted activation energies are in fine agreement with the observed reaction rates. An alternative approach, which uses the tetrahedral intermediate as the transition state mimic, provides satisfactory predictions.