Asymmetric hydrogenation with chiral aminophosphine-rhodium complexes and chiral recognition by bisphosphine-rhodium complexes in the asymmetric hydrogenation of olefins through the chiral helical conformation of phenyl groups on the phosphorus atom.

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The asymmetric hydrogenation of α-acylaminocinnamic acids with the rhodium complex of (1R,2R)-1,2-bis(N-diphenylphosphino-N-methylamino)cyclohexane has been reported to give preferentially (S)-amino acids. On the contrary, it has been found that the enantiomeric (R)-amino acids are obtained by hydrogenation with the rhodium complex of (1R,2R)-1,2-bis(diphenylphosphinamino)cyclohexane. The study of the inversion of the stereoselectivity of the rhodium complex of (1R,2R)-1,2-bis(diphenylphosphinamino)cyclohexane by the N-methylation of the ligand in asymmetric hydrogenation has been described. From stereochemical considerations, the chiral helical conformation of the phenyl groups attached on the phosphorus in bisphosphine-rhodium complexes may be responsible for the induced chirality of the product of the hydrogenation. A complex with a left-handed helicity would give (R)-amino acid, and a complex with a right-handed helicity would give (S)-amino acid. The effects of the solvents and substrate structures on the optical yields are also discussed.

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