Electronic effects on enantioselectivity in epoxidation catalyzed by D4-symmetric chiral porphyrins

Abstract

Asymmetric epoxidation of various aromatic olefins was examined with our D 4-symmetric chiral porphyrin. The enantioselectivity was greatly improved upon when the substrates contained electron-deficient groups. Moreover, examination of electronic effects in the porphyrin catalyst revealed that electron-deficient groups lowered and electron-donating groups raised the enantioselectivity. Hammett plot analysis suggested that these electronic effects could be interpreted in terms of the Hammond postulate.