THE ASYMMETRIC HYDROGENATION OF α-KETO ESTERS CATALYZED BY RHODIUM(I) COMPLEXES WITH CHIRAL DIPHOSPHINE LIGANDS. ON THE CATALYTIC CYCLES AND THE MECHANISM OF ASYMMETRIC INDUCTION

Article abstract of DOI:10.1016/S0022-328X(00)90008-1

Asymmetric hydrogenations of n-propyl pyruvate and ketopantoyl lactone catalyzed by rhodium complexes with (-) DIOP and BPPM were carried out under a variety of conditions.It was found that i) the Schrock-Osborn mechanism was not operative in these reactions at all since no acceleration of the reaction rate by the addition of water (1percent) was observed, ii) there was a clear difference between cationic and neutral (in situ) rhodium catalysts in their enantioslectivity, and iii) there was a remarkable solvent effect on the extent and direction of asymmetric induction.Possible mechanisms are discussed on the basis of these results.