Readily available chiral phosphine–aminophosphine ligands derived from 1-phenylethylamine for Rh-catalyzed enantioselective hydrogenations

A series of new chiral phosphine–aminophosphine ligands have been prepared via a two- or three-step transformation from commercially available and inexpensive (S)-1-phenylethylamine, and successfully used in the rhodium-catalyzed asymmetric hydrogenation of various enamides, β-dehydroamino acid esters, and dimethyl itaconate. The results show that the ligand structure plays an important influence on both the reactivity and enantioselectivity. Ligand 2d bearing a N–H proton and two F-atoms on the 3,5-positions of the phenyl ring of the aminophosphino moiety was most effective for the hydrogenation of enamides and (Z)-β-aryl-β-(acylamino)acrylates, whereas ligand 1b showed the highest enantioselectivities in the hydrogenation of (Z)-β-alkyl-β-(acylamino)acrylates and dimethyl itaconate.

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N-[Bis(4-trifluoromethylphenyl)phosphino]-(S)-1-[2-(diphenylphosphino)phenyl]ethylamineC34H27F6NP2Ee >98%[α]D25=+3.2 (c 0.72, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

N-[Bis(4-methylphenyl)phosphino]-(S)-1-[2-(diphenylphosphino)phenyl]ethylamineC34H33NP2Ee >98%[α]D25=-5.2 (c 0.25, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

N-{Bis[3,5-bis(trifluoromethyl)phenyl]phosphino}-(S)-1-[2-(diphenylphosphino)phenyl]ethylamineC36H25F12NP2Ee >98%[α]D25=+24.7 (c 0.59, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

N-[Bis(3,5-difluorophenyl)phosphino]-(S)-1-[2-(diphenylphosphino)phenyl]ethylamineC32H25F4NP2Ee >98%[α]D25=+10.2 (c 1.35, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

N-Methyl-N-[bis(4-trifluoromethylphenyl)phosphino]-(S)-1-[2-(diphenylphosphino)phenyl]ethylamineC35H29F6NP2Ee >98%[α]D25==+56.0 (c 1.16, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

N-Methyl-N-[bis(4-methylphenyl)phosphino]-(S)-1-[2-(diphenyl-phosphino)phenyl]ethylamineC35H35NP2Ee >98%[α]D25=+44.4 (c 0.70, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

N-Methyl-N-{bis[3,5-bis(trifluoromethyl)phenyl]phosphino}-(S)-1-[2-(diphenylphosphino)phenyl]ethylamineC37H27F12NP2Ee >98%[α]D25=+58.7 (c 0.16, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)

N-Methyl-N-[bis(3,5-difluorophenyl)phosphino]-(S)-1-[2-(diphenylphosphino)phenyl]ethylamineC33H27F4NP2Ee >98%[α]D25=+54.8 (c 0.45, ClCH2CH2Cl)Source of chirality: (S)-1-phenylethylamineAbsolute configuration: (S)