CHIRAL SULFONATED PHOSPHINES - RHODIUM(I)-CATALYZED ASYMMETRIC HYDROGENOLYSIS OF EPOXIDES

Rhodium(I) complexes of sulfonated (-)-(2S,4S)-2,4-bis(diphenylphosphi no)pentane ((S,S)-(BDPP)) are effective as catalyst for asymmetric hyd rogenolysis of sodium cis-epoxysuccinate to sodium hydroxysuccinate in aqueous-organic two phase solvent system or in aqueous solution. It h as been shown by deuterium labelling studies that both hydrogen and wa ter participate in the aqueous hydrogenolysis as reactants and the rea ction proceeds via the direct C-O bond cleavage of the epoxy group. Hi gh pressure NMR studies show the presence of rhodaoxetane-BDPP complex es as catalytic intermediates, which an formed by the oxidative additi on of the epoxide to unsaturated Rh(I) species. Accordingly, a reactio n mechanism has been proposed for the aqueous catalytic process. The u se of a racemic substrate, sodium trans-phenylglycidate with the aqueo us Rh-sulfonated (S,S)-BDPP system results in the kinetic resolution o f the (2S,3R)-epoxide enantiomer. Thus, asymmetric aqueous catalytic h ydrogenolysis could be a useful synthetic approach not only to chiral alpha-hydroxycarboxylic acid derivatives but also to chiral trans-subs tituted epoxides.