N-Heterocyclic Carbene (NHC)-Catalyzed Cycloaddition Reactions of Enals and Ynals

The use of alpha,beta-unsaturated aldehydes (enals) was first introduced into the context of N-heterocyclic carbene (NHC) mediated gamma-butyrolactone formations, which was developed independently by our laboratory and that of Glorius'. This finding revealed the fascinating properties of reactive intermediates catalytically accessible via nucleophilic addition of NHC to enals.;We have developed NHC-catalyzed enantioselective benzoin-oxy-Cope annulations for the syntheses of cyclopentenes. To overcome the limitation of substrate scope and maintain the stereochemical information, the use of alpha'-hydroxyenones allowed us to access bicyclo-beta-lactone adducts. This annulation also showed that the otherwise identical triazolium and imidazolium-derived NHC-catalysts affect the stereodivergent transformations.;The role of base was crucial to the catalytic generation of the reactive intermediates from the combination of NHC and enals. We found that the use of weak amine bases allowed us to access a catalytic generation of enolates, which readily undergo oxo-Diels-Alder reaction.;Catalytic asymmetric Claisen rearrangement has remained a challenging task. We have reveled alpha,beta-unsaturated acyl azolium---catalytically generated from NHC and ynals---was an intriguing platform for catalytic highly enantioselective Coates-Claisen rearrangement when coupled with enolic compounds.