N-Heterocyclic Carbeen Catalyzed Annulation Ofα-Functionalized Aldehyde

N-Heterocyclic carbenes (NHCs) have been shown to be useful catalysts in the field of organocatalysis. The Breslow intermediate catalytically generated from the nucleophilic addition of NHC to a-functionalized aldehyde undergoes umpolung transformation into several active species. The research of these active species are undergoing throughout the world.Several traditional methods have been employed to prepare coumarins, however, they have many drawbacks. The active enolate catalytically generated from the tautomerization and protonation of Breslow intermediate could undergoes Aldol condensation and esterification with salicylaldehyde leading to coumarin in mild condition. My major work is listed as follow:1. The Breslow intermediate catalytically generated from addition of NHC to cinnamaldehyde derivatives underwent tautomerization and proton transference leading to3-arylpropenolate.3-Benzylcoumarin derivatives could be readily formed from the annulations of the3-arylpropenolate with salicylaldehyde. This pathway was also available for3-ethylcoumarin.2. The adduct catalytically generated from NHC and2-chloro-2-arylaldehyde underwent elimination leading to an enolate equivalent. Aryl acyl azolium generated from Aldol condensation of the enolate equivalent with salicylaldehyde underwent internal esterification leading to3-arylcoumarin in mild condition. This reaction was compatible with functional groups like ester group, extra hydroxyl and amide group.