Chiral sulfonated phosphines. Rhodium(I)-catalyzed asymmetric hydrogenolysis of epoxides

Rhodium(I) complexes of sulfonated (-)-(2S,4S)-2,4-bis(diphenylphosphino)pentane ((S,S)-(BDPP)) are effective as catalyst for asymmetric hydrogenolysis of sodium cis-epoxysuccinate to sodium hydroxysuccinate in aqueous-organic two phase solvent system or in aqueous solution. It has been shown by deuterium labelling studies that both hydrogen and water participate in the aqueous hydrogenolysis as reactants and the reaction proceeds via the direct C-O bond cleavage of the epoxy group. High pressure NMR studies show the presence of rhodaoxetane-BDPP complexes as catalytic intermediates, which an formed by the oxidative addition of the epoxide to unsaturated Rh(I) species. Accordingly, a reaction mechanism has been proposed for the aqueous catalytic process. The use of a racemic substrate, sodium trans-phenylglycidate with the aqueous Rh-sulfonated (S,S)-BDPP system results in the kinetic resolution of the (2S,3R)-epoxide enantiomer. Thus, asymmetric aqueous catalytic hydrogenolysis could be a useful synthetic approach not only to chiral alpha-hydroxycarboxylic acid derivatives but also to chiral trans-substituted epoxides.