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4140776 
Journal Article 
Rigid P-chiral phosphine ligands with tert-butylmethylphosphino groups for rhodium-catalyzed asymmetric hydrogenation of functionalized alkenes 
Imamoto, T; Tamura, K; Zhang, Z; Horiuchi, Y; Sugiya, M; Yoshida, K; Yanagisawa, A; Gridnev, ID 
2012 
Yes 
Journal of the American Chemical Society
ISSN: 0002-7863
EISSN: 1520-5126 
134 
3 
1754-1769 
English 
22192064 
WOS:000301084400062 
Both enantiomers of 2,3-bis(tert-butylmethylphosphino)quinoxaline (QuinoxP*), 1,2-bis(tert-butylmethylphosphino)benzene (BenzP*), and 1,2-bis(tert-butylmethylphosphino)-4,5-(methylenedioxy)benzene (DioxyBenzP*) were prepared in short steps from enantiopure (S)- and (R)-tert-butylmethylphosphine-boranes as the key intermediates. All of these ligands were crystalline solids and were not readily oxidized on exposure to air. Their rhodium complexes exhibited excellent enantioselectivities and high catalytic activities in the asymmetric hydrogenation of functionalized alkenes, such as dehydroamino acid derivatives and enamides. The practical utility of these catalysts was demonstrated by the efficient preparation of several chiral pharmaceutical ingredients having an amino acid or a secondary amine component. A rhodium complex of the structurally simple ligand BenzP* was used for the mechanistic study of asymmetric hydrogenation. Low-temperature NMR studies together with DFT calculations using methyl α-acetamidocinnamate as the standard model substrate revealed new aspects of the reaction pathways and the enantioselection mechanism.