Synthesis of amino acid derived imidazolidinium salts as new NHC precatalysts

The preparation of new chiral symmetrically and unsymmetrically N,N′-disubstituted imidazolium based NHC salts Ib, IIb, IIIa–c and IVc–h from the amino acids l-proline and l-phenylalanine, is reported. Some preliminary tests have been carried out, demonstrating that the chiral NHCs give chiral induction in organometallic catalysis and can be used as organocatalysts.

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1,3-Bis(2-((2S)-2-(methoxymethyl)pyrrolidin-1-yl)phenyl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphate(V)C27H37N4O2PF6[α]D20=+177 (c 0.24, CH3OH)Source of chirality: l-prolineAbsolute configuration: (2′S)

(2S)-3-(3,5-Dimethylphenyl)-1-(2-(2-(methoxymethyl)pyrrolidin-1-yl)phenyl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC23H30N3OPF6[α]D20=+2.0 (c 0.19, CH3OH)Source of chirality: l-prolineAbsolute configuration: (2′S)

(2S)-1-(2-(2-(Hydroxymethyl)pyrrolidin-1-yl)phenyl)-3-mesityl-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC23H30N3OPF6[α]D20=+30.0 (c 0.3, CH3OH)Source of chirality: l-prolineAbsolute configuration: (2′S)

(2S)-1-(2-(2-((tert-Butyldimethylsilyloxy)methyl)pyrrolidin-1-yl)phenyl)-3-mesityl-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC29H44N3OSiPF6[α]D20=+43.0 (c 0.65, CH3OH)Source of chirality: l-prolineAbsolute configuration: (2′S)

(2S)-3-(2,6-Diisopropylphenyl)-1-(1-hydroxy-3-phenylpropan-2-yl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC24H33N2OPF6[α]D20=-60.6 (c 1.03, acetone)Source of chirality: l-phenylalanineAbsolute configuration: (2′S)

(2S)-3-(2,6-Diisopropylphenyl)-1-(1-(methylsulfonyloxy)-3-phenylpropan-2-yl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC25H35N2O3SPF6[α]D20=-51.5 (c 1.02, acetone)Source of chirality: l-phenylalanineAbsolute configuration: (2′S)

(2S)-1-(1-Acetoxy-3-phenylpropan-2-yl)-3-(2,6-diisopropylphenyl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC26H35N2O2PF6[α]D20=-46.6 (c 1.02, acetone)Source of chirality: l-phenylalanineAbsolute configuration: (2′S)

(2S)-3-(2,6-Diisopropylphenyl)-1-(1-phenyl-3-(pivaloyloxy)propan-2-yl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC29H41N2O2PF6[α]D20=-46.7 (c 1.04, acetone)Source of chirality: l-phenylalanineAbsolute configuration: (2′S)

(2S)-1-(1-(Benzoyloxy)-3-phenylpropan-2-yl)-3-(2,6-diisopropylphenyl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC31H37N2O2PF6[α]D20=-33.3 (c 1.01, acetone)Source of chirality: l-phenylalanineAbsolute configuration: (2′S)

(2S)-3-(2,6-Diisopropylphenyl)-1-(1-(trimethylsilyl)-3-phenylpropan-2-yl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC27H41N2OSiPF6[α]D20=-47.1 (c 1.03, acetone)Source of chirality: l-phenylalanineAbsolute configuration: (2′S)

(2S)-3-(2,6-Diisopropylphenyl)-1-(1-(t-butyldimethylsilyl)-3-phenylpropan-2-yl)-4,5-dihydro-1H-imidazol-3-ium hexafluorophosphateC30H47N2OSiPF6[α]D20=-43.7 (c 1.01, acetone)Source of chirality: l-phenylalanineAbsolute configuration: (2′S)