M C. White, Chem 153 Hydrogenation -153 Week of october 15. 2002 Origin of Asymmetric Induction (CO4) It was concluded from kinetic measurements that the minor diastereomer was 580 fold more reactive towards H, oxidative addition (recall the rds at rt) This factor offsets its lower concentration in olution and results in a 60: 1 product ratio in favor of the r enantiomer (S,S-CHIRAPHOS /(rDCO2Et CO,H H,(1 atm), 25C, MeOH NHA NHAc N-acetyI-(R)-phenylalanine >95%ee stereospecific H migratory insertion/ stereospecific H/C reductive elimination both to the olefin face bound to rh (C1O4) HN/CO2Me H3C MeO2C、NH olefin bound R to rh via its H3C olefin bound to rh via major diastereomer formed minor diastereomer formed in solution(identified by NMR one detected by nmr(must be and x-ray crystallography) less than 5% present in solution) HalM.C. White, Chem 153 Hydrogenation -153- Week of October 15, 2002 Origin of Asymmetric Induction It was concluded from kinetic measurements that the minor diastereomer was 580 fold more reactive towards H2 oxidative addition (recall the RDS at rt). This factor offsets its lower concentration in solution and results in a 60:1 product ratio in favor of the R enantiomer. Halpern Science 1982 (217) 401. CO2H NHAc H2 (1 atm), 25oC, MeOH CO2Et NHAc N-acetyl-(R)-phenylalanine >95% ee (R) Rh(I) P P (ClO4-) + H3C H3C (S,S-CHIRAPHOS) Rh(I) P P O NH (ClO4-) + H3C H3C MeO2C Ph olefin bound to Rh via its si-face stereospecific H migratory insertion / stereospecific H/C reductive elimination both to the olefin face bound to Rh minor diastereomer formed none detected by NMR (must be less than 5% present in solution) Rh(I) P O P HN (ClO4-) + CH3 CH3 CO2Me Ph olefin bound to Rh via its re-face major diastereomer formed in solution (identified by NMR and x-ray crystallography)