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-alpha,beta-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.

A new synthetic approach to chiral imidazolium salts makes possible the first synthesis of an N-mesityl substituted, aminoindanol-derived N-heterocyclic carbene precursor, 1.ClO4. The successful synthesis allows the first direct comparison of otherwise identical imidazolium and triazolium precursors across a number of NHC-catalyzed processes. These studies confirm striking differences in reactivity and mechanism between the two classes.

2,4,6‐Trimethylaniline Hydrogen chloride Sodium nitrite Tin(II) chloride dihydrate Trimethyloxonium tetrafluoroborate Hydrogen chloride, dioxane solution 2‐Mesitylhydrazinium chloride Chlorobenzene Triethyl orthoformate (5a R ,10bS)‐5a,10b‐Dihydro‐2‐(2,4,6‐trimethylphenyl)‐4 H, 6H ‐ indeno[2,1 b ]‐1,2,4‐triazolo[4,3‐ d ]‐1,4‐oxazinium chloride

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