Asymmetric Hydrogenation of Ketones and Imines with Poly-Coordinated Chiral Catalysts

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A series of ruthenium complexes with both chiral diphosphine and diamine ligands was designed and applied to asymmetric hydrogenation of ketones. The obtained results are described below1) Chiral 1,4-diamine IPHAN was prepared from mannitol. The TolBINAP/IPHAN-Ru complex effectively catalyzed asymmetric hydrogenation of 1-tetralones and their analogues in a base containing 2-propanol. The reaction was completed with a substrate-to-catalyst molar ratio (S/C) as high as 55,000 to afford the chiral alcohols in up to 99% enantiomeric excess (ee). Substituted 2-cyclohexenones were also converted to the allylic alcohols in high ee.2) The TolBINAP/PICA-Ru catalyst (PICA=α-picolylamine) achieved asymmetric hydrogenation of tert-alkyl ketones. A series of sterically hindered ketones was hydrogenated with an S/C as high as 100,000 at 20 atm H_2 to produce the chiral alcohols in up to 98% ee.3) A library of Ru complexes with chiral diphosphine ligands and chiral diamine ligands was made for systematic screening of chiral catalysts in asymmetric hydrogenation of various ketones. For this purpose, a series of chiral 1,2-diamine ligands was prepared from amino acids. Among of them a chiral N,N-dimethyl-1,2-diamine, DMAPEN, showed unique features. The TolBINAP/DMAPEN-Ru catalyzed hydrogenation of arylglyoxal dialkylacetals afforded the α-hydroxy acetals in up to 98% ee.4) Aromatic imines were hydrogenated with chiral Ru complexes under basic conditions.5) LiCl, one of the simplest lithium salts, efficiently catalyzed a reaction of aldehydes and (CH_3)_3SiCN under solvent free conditions. The cyanosilylation of a series of aromatic, aliphatic, and vinylic aldehydes completed with an S/C as high as 100,000 at ambient temperature.Topics 1) to 3) have expanded into collaboration projects with chemical industries.The investigator (Takeshi Ohkuma) received JSPS Prize from Japan Society for the Promotion of Science in 2007.