M.C. White Chem 153 Hydrogenation -144- Week of october 15. 2002 Wilkinson: diastereoselectivity Ph3 Ba,, PPh3 PhaP Cl I mol% H2 (1 atm. ) benzene/EtoH, rt R=H: 73%endo R=Me 92%endo R Rationale for observed diastereoselectivity Olefin binds the catalyst from the least sterically hindered exo face. Subsequent cis hydrometallation of the exo face followed by stereospecific reductive elimination of Ph3 Pu, the alkyl metal hydrido intermediate results in overall cis addition of H, to the leas sterically hindered exo face of the olefin. Rousseau J. Mol. Cat. 1979(5)163 Jardine Prog. Inorg. Chem. 1981(28)63 olefin complexation and hydrogenation from sterically less hindered face Ph3p a PPha Bno OMOM OMOM 30mo% H2(I atm ) tol, rt OBn Lowary OL 2000(2)167M.C. White, Chem 153 Hydrogenation -144- Week of October 15, 2002 Wilkinson: diastereoselectivity Ph3P Rh(I) Ph3P PPh3 Cl 1 mol% H2 (1 atm.), benzene/EtOH, rt Me H endo exo Me R R R R = H : 73% endo R = Me : 92% endo Rationale for observed diastereoselectivity: Olefin binds the catalyst from the least sterically hindered exo face. Subsequent cis hydrometallation of the exo face followed by stereospecific reductive elimination of the alkyl metal hydrido intermediate results in overall cis addition of H2 to the least sterically hindered exo face of the olefin. Cl Rh(III) Ph3P H PPh3 H R vs. Cl Rh(III) Ph3P H PPh3 H R Rousseau J. Mol. Cat. 1979 (5) 163. Jardine Prog. Inorg. Chem. 1981 (28) 63. BnO OMOM BnO OBn olefin complexation and hydrogenation from sterically less hindered face Ph3P Rh(I) Ph3P PPh3 Cl 30 mol% H2 (1 atm.), tol, rt 83% BnO OMOM BnO Lowary OBn OL 2000 (2) 167