Acyl anion free N-heterocyclic carbene organocatalysis.

Reaction discovery using N-heterocyclic carbene organocatalysis has been dominated by the chemistry of acyl anion equivalents. Recent studies demonstrate that NHCs are far more diverse catalysts, with a variety of reactions discovered that proceed without acyl anion equivalent formation. In this tutorial review selected examples of acyl anion free NHC catalysis using carbonyl compounds are presented.