Ligand and substrate π-stacking interaction controlled enantioselectivity in the asymmetric aziridination

Both the steric hindrance and the electronic effect are important factors for controlling the enantioselectivity in asymmetric catalysis. The substituent-dependent enantioselectivity in the asymmetric aziridination of chalcones catalyzed by 1,8-anthracene-linked bis-oxazoline (AnBOX) was rationalized to the π-stacking interaction between the ligand backbone and substrates and primarily confirmed by the use of bulky substrates and catalysts without aromatic backbones. The results provide important information for designing novel ligands and for understanding the influence of the electronic effect in asymmetric catalysis.

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(2S,3R)-3-Phenyl-2-(4-trifluoromethylbenzoyl)-1-(p-tolylsulfonyl)aziridineC23H18F3NO3SEe = 44%[α]D16=+8.85 (c 0.87, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3R)

(2R,3S)-3-Phenyl-2-(4-trifluoromethylbenzoyl)-1-(p-tolylsulfonyl)aziridineC23H18F3NO3SEe = 65%[α]D16=-13.9 (c 1.0, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2R,3S)

(2S,3R)-2-(4-Isopropylbenzoyl)-3-phenyl-1-(p-tolylsulfonyl)aziridineC25H25NO3SEe = 66%[α]D20=+5.7 (c 0.80, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3R)

(2R,3S)-2-(4-Isopropylbenzoyl)-3-phenyl-1-(p-tolylsulfonyl)aziridineC25H25NO3SEe = 85%[α]D20=-7.3 (c 1.00, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2R,3S)

(2S,3R)-2-(4-tert-Butylbenzoyl)-3-phenyl-1-(p-tolylsulfonyl)aziridineC26H27NO3SEe = 70%[α]D20=+5.1 (c 0.81, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3R)

(2R,3S)-2-(4-tert-Butylbenzoyl)-3-phenyl-1-(p-tolylsulfonyl)aziridineC26H27NO3SEe = 98%[α]D20=-6.1 (c 0.66, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2R,3S)

(2S,3R)-2-(4-tert-Butylbenzoyl)-3-tolyl-1-(p-tolylsulfonyl)aziridineC27H29NO3SEe = 71%[α]D20=-3.4 (c 0.76, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3R)

(2R,3S)-2-(4-tert-Butylbenzoyl)-3-tolyl-1-(p-tolylsulfonyl)aziridineC27H29NO3SEe = 89%[α]D20=+4.6 (c 0.65, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2R,3S)

(2S,3R)-3-Phenyl-2-(trans-4-propylcyclohexylformyl)-1-(p-tolylsulfonyl)aziridineC25H31NO3SEe = 48%[α]D20=+5.05 (c 1.00, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2S,3R)

(2R,3S)-3-Phenyl-2-(trans-4-propylcyclohexylformyl)-1-(p-tolylsulfonyl)aziridineC25H31NO3SEe = 30%[α]D20=-3.0 (c 1.00, CHCl3)Source of chirality: asymmetric synthesisAbsolute configuration: (2R,3S)