Asymmetric hydrogenation of enamides with a new chiral phosphine–phosphinite ligand

A new mixed chiral phosphine–phosphinite 4 obtained from enantiomerically pure (S)-(+)-3-boronatodiphenyl-phosphanyl butanoic acid 1 was synthesized in four steps. This new chiral ligand was used in the asymmetric hydrogenation of dehydroamino acids with enantioselectivities being obtained of up to 90.8%.

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3-(S)-Boronatodiphenylphosphanyl-butanoic acidC16H20BO2PEe>98% (HPLC)[α]D20=+28.7 (c 1.02, CHCl3)Source of chirality: diastereoselective synthesisAbsolute configuration: 3S

3-(S)-Boronatodiphenylphosphanyl-butanolC16H22BOPEe>98%[α]D20=+5.0 (c 1.1, CHCl3)Source of chirality: diastereoselective synthesisAbsolute configuration: 3S

3-(S)-Diphenylphosphanyl-butanolC16H19OPEe>98%[α]D20=-2.3 (c 1.0, CHCl3)Source of chirality: diastereoselective synthesisAbsolute configuration: 3S

3-(S)-Diphenylphosphanyl-1-diphenylphosphinite butaneC28H28OP2Ee>98%[α]D20=+4.5 (c 1.1, CHCl3)Source of chirality: diastereoselective synthesisAbsolute configuration: 3S