Theoretical model for N-heterocyclic carbene-catalyzed decarboxylation reactions

Identifying the special role of N-heterocyclic carbene (NHC) remains one of the most important challenges in the field of organocatalysis. Herein, we proposed a theoretical model for NHC-catalyzed decarboxylation reactions, and performed DFT calculations in two selected cases of NHC-mediated reactions involving possible decarboxylation processes. The calculation results indicate that NHC not only works as a Lewis base to promote cyclization, as NHC center dot H+ works as hydrogen bond donor to facilitate CO2 release, which is remarkably different from the proposed role of Lewis bases in previous reports. Further analysis indicates that C-HMIDLINE HORIZONTAL ELLIPSISO hydrogen bond interactions contribute significantly to controlling stereoselectivity in these kinds of reactions.