New chiral 1,3-diphosphine ligands for Rh-catalyzed enantioselective hydrogenation: a search for electronic effects

New electron-rich chiral 1,3-diphosphines of the BDPP type were prepared from 1,3-diphenylpropane-1,3-diol by an economically feasible synthetic approach. The σ-donor properties of the phosphines were determined by measurement of J(31P–77Se) coupling constants in the corresponding phosphine selenides. For comparison related, but electronically different, 1,3-diphosphines were considered. The new diphosphines showed good enantioselectivities as ligands in the Rh-catalyzed enantioselective hydrogenation of benchmark substrates and β-amino acid precursors (up to 98% ee). The electronic effects on the outcome of the enantioselective catalysis have been analyzed.

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(S,S)-1,3-Bismethanesulfonyloxy-1,3-dicyclohexylpropaneC17H32O6S2De = >99%, ee = >99%[α]D23=-62.4 (c 1.2, CH3Cl)Source of chirality: asymmetric hydrogenationAbsolute configuration: S,S

(R,R)-Bis(diphenylphosphino)-1,3-dicyclohexylpropaneC39H46P2De = >99%, ee = >99%[α]D20=-58 (c 0.6, C6H6)Source of chirality: asymmetric hydrogenationAbsolute configuration: R,R

(R,R)-Bis[(di-p-tolyl)phosphino]-1,3-dicyclohexylpropaneC43H54P2De = >99%, ee = >99%[α]D22=-18 (c 0.6, C6H6)Source of chirality: asymmetric hydrogenationAbsolute configuration: R,R