N ‐Heterocyclic Carbene‐Catalyzed Kinetic Resolution of 3‐Nitro‐1,2‐Dihydroquinolines: Asymmetric Synthesis of All C 2 ‐, C 3 ‐ and C 4 ‐Functionalized Tetrahydroquinolines

An efficient N ‐heterocyclic carbene (NHC)‐catalyzed kinetic resolution of 2‐substituted 3‐nitro‐1,2‐dihydroquinolines (DHQs) allowing the synthesis of densely functionalized enantioenriched tetrahydroquinolines through the resolution at remote stereocenter is described. The Re ‐face addition of α , β ‐unsaturated azolium homoenolate intermediate generated in situ from enal with the more kinetically favored (S)‐enantiomer of the racemic 2‐substituted 3‐nitro‐1,2‐dihydroquinolines ( rac ‐ 1 ), affording the enantiopure tetrahydroquinolines (up to >99 : 1 dr , >99 : 1 er ) and the opposite ( R )‐enantiomer of DHQ ( ent ‐ 1 ) was recovered (up to >99 : 1 er ).