Background:
During the last two decades, horizon of research in the field of Nitrogen Heterocyclic Carbenes
(NHC) has widened remarkably. NHCs have emerged as ubiquitous species having applications in a broad range of fields,
including organocatalysis and organometallic chemistry. The NHC-induced non-asymmetric catalysis has turned out to be
a really fruitful area of research in recent years.
Methods:
By manipulating structural features and selecting appropriate substituent groups, it has been possible to control
the kinetic and thermodynamic stability of a wide range of NHCs, which can be tolerant to a variety of functional groups
and can be used under mild conditions. NHCs are produced by different methods, such as deprotonation of Nalkylhetrocyclic salt, transmetallation, decarboxylation and electrochemical reduction.
Results:
The NHCs have been used successfully as catalysts for a wide range of reactions making a large number of building
blocks and other useful compounds accessible. Some of these reactions are: benzoin condensation, Stetter reaction, Michael
reaction, esterification, activation of esters, activation of isocyanides, polymerization, different cycloaddition reactions,
isomerization, etc. The present review includes all these examples published during the last 10 years, i.e. from 2010 till date.
Conclusion:
The NHCs have emerged as versatile and powerful organocatalysts in synthetic organic chemistry. They
provide the synthetic strategy which does not burden the environment with metal pollutants and thus fit in the Green
Chemistry.
NHC-catalysed benzoin condensation – is it all down to the Breslow intermediate?
