Highly Enantioselective Azadiene Diels−Alder Reactions Catalyzed by Chiral N-Heterocyclic Carbenes

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Abstract
Highly enantioselective, N-heterocyclic carbene (NHC)-catalyzed aza-Diels−Alder reactions are described. A novel chiral triazolium salt based on the cis-1,2-aminoindanol platform serves as an efficient precatalyst for the NHC-catalyzed redox generation of enolate dienophiles that undergo LUMOdiene-controlled Diels−Alder reactions with N-sulfonyl-α,β-unsaturated imines in good yields and with exceptional diastereo- and enantioselectivities (>99% ee). In contrast to uncatalyzed variants, this organocatalytic process proceeds at room temperature without stoichiometric reagents, producing synthetically valuable, enantiomerically pure cis-3,4-disubstituted dihydropyridinone products.