N-heterocyclic carbene catalyzed umpolung of styrenes: mechanistic elucidation and selective tail-to-tail dimerization.

The reaction between N-heterocyclic carbenes (NHCs) and styrenes yields alkyl-substituted azolium salts, which are able to form nucleophilic deoxy Breslow intermediates by simple deprotonation. This hitherto unknown reaction of NHCs represents a new way to generate deoxy Breslow intermediates and paves the way for the selective NHC-catalyzed tail-to-tail homodimerization of styrenes. This reaction significantly broadens the scope of the Michael umpolung and provides a new method to generate 1,4-diaryl compounds.

Highly enantioselective intermolecular Stetter reaction of simple acrylates: synthesis of α-chiral γ-ketoesters.

Simple Stetter: A novel N-heterocyclic carbene (NHC) was designed by combining an electron-rich 2,6-dimethoxy substituent and an underestimated yet promising chiral motif. With this NHC in hand, a highly enantioselective intermolecular Stetter reaction of simple acrylates was developed, yielding versatile α-chiral γ-ketoesters. This represents the first catalytic asymmetric route towards these valuable compounds (see scheme).

N-heterocyclic carbene-catalyzed cascade reaction involving the hydroacylation of unactivated alkynes.

The N-heterocyclic carbene (NHC)-catalyzed hydroacylation of unactivated alkynes to provide alpha,beta-unsaturated ketones is reported. In addition, a rare case of an efficient and selective dually NHC-catalyzed cascade reaction involving the hydroacylation of alkynes and a subsequent intermolecular Stetter reaction allows the formation of chromanones containing a 1,4-diketone moiety.