Enantioselective epoxidation of trans-disubstituted alkenes by D2-symmetric chiral dioxoruthenium(VI) porphyrins

Abstract

A series of D2-symmetric chiral trans-dioxoruthenium(VI) porphyrins bifacially encumbered by four threitol units with staggered conformation can react favorably with trans-alkenes in exceptional percentages of enantiomeric excess up to 70% and 76% enantiomeric excess are achieved for the epoxidation of trans-β-methylstyrene and cinnamyl chloride, respectively. Much lower enantioselectivity, however, is obtained for the cis-β-methylstyrene. Oxidation by these complexes exhibits clean pseudo-first-order kinetics. The trans-alkene oxidation gives a higher second-order rate constant k2 compared with that of the analogous cis-isomer. A 'head-on approach' model elucidates the stereoselectivity for the trans-preference oxidation. Original is an abstract.