N-Heterocyclic Carbene Organocatalysis: With or Without Carbenes?

ABSTRACT: In this work the mechanism of the aldehyde umpolung reactions, catalyzed by azolium cations in the presence of bases, was studied through computational methods. Next to the mechanism established by Breslow in the 1950s that takes effect through the formation of a free carbene, we have suggested that these processes can follow a concerted asynchronous path, in which the azolium cation directly reacts with the substrate, avoiding the formation of the carbene intermediate. We hereby show that substituting the azolium cation, and varying the base or the substrate do not affect the preference for the concerted reaction mechanism. The concerted path was found to exhibit low barriers also for the reactions of thiamine with model substrates, showing that this path might have biological relevance.

SUBMITTER: Gehrke S 

PROVIDER: S-EPMC7496998 | biostudies-literature | 2020 Aug

REPOSITORIES: biostudies-literature