Enantioselective NHC-Catalyzed Redox [4 + 2]-Hetero-Diels-Alder Reactions Using α,β-Unsaturated Trichloromethyl Ketones as Amide Equivalents

α,β-Unsaturated trichloromethyl ketones are suitable α,β-unsaturated amide and ester equivalents in N-heterocyclic carbene (NHC)-catalyzed redox hetero-Diels-Alder reactions with azolium enolates generated from α-aroyloxyaldehydes. The initially formed syn-dihydropyranone products can be isolated or can undergo ring-opening with benzylamine followed by aminolysis of the resulting CCl₃ ketone to form a range of diamides with high diastereo- and enantioselectivity (up to >95:5 dr and >99% ee).