A novel C2-symmetric bisphosphane ligand with a chiral cyclopropane backbone: synthesis and application in the Rh(I)-catalyzed asymmetric 1,4-addition of arylboronic acids

The synthesis of a novel C2-symmetric bisphosphane ligand was accomplished starting from trans-(2R,3R)-bis(3′,5′-diphenylphenyl)cyclopropane-1,1-dimethanol as a key intermediate. This ligand was tested in the asymmetric rhodium(I)-catalyzed 1,4-addition to cyclic enones. We also compared the new ligand with a similar phosphane ligand with a less bulky cyclopropane backbone. Good yields (up to 99%) and enantioselectivities (up to 89% ee) were observed. We demonstrated that the presence of a more bulky cyclopropane backbone resulted in a less effective ligand.

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(2R,3R)-1,1-Bis[(diphenylphosphanyl)methyl]-2,3-bis(3′,5′-diphenylphenyl)-cyclopropaneC65H52P2[α]D20=+95.3 (c 1.0, CHCl3)Source of chirality: Sharpless asymmetric dihydroxylationAbsolute configuration: (2R,3R)