The asymmetric epoxidation of a,b-enones by the readily available bis(3,5-dimethylphenyl)-(S)- pyrrolidin-2-ylmethanol and tert-butyl hydroperoxide (TBHP) is described. Stereoelectronic substitution on the aryl moiety of diaryl-2-pyrrolidinemethanols was found to significantly affect the efficiency with respect to the previously reported (S)-diphenyl-2-pyrrolidinemethanol. Improved reactivity and enantioselectivity were achieved with bis(3,5-dimethylphenyl)- (S)-pyrrolidin-2-ylmethanol at reduced catalyst loading (20 mol %) with ees up to 94% for chalcone epoxides under mild reaction conditions, whereas (S)-diphenyl- 2-pyrrolidinemethanol afforded a maximum ee of 80%. Interestingly, the methodology is applicable to the epoxidation of more challenging aliphatic or enolizable enones with good control of the asymmetric induction (up to 87% ee).
Bis-(3,5-dimethylphenyl)-(S)-pyrrolidin-2-yl-methanol: an improved organocatalyst for the asymmetric epoxidation of a,b-enones
LATTANZI, Alessandra
2006-01-01
Abstract
The asymmetric epoxidation of a,b-enones by the readily available bis(3,5-dimethylphenyl)-(S)- pyrrolidin-2-ylmethanol and tert-butyl hydroperoxide (TBHP) is described. Stereoelectronic substitution on the aryl moiety of diaryl-2-pyrrolidinemethanols was found to significantly affect the efficiency with respect to the previously reported (S)-diphenyl-2-pyrrolidinemethanol. Improved reactivity and enantioselectivity were achieved with bis(3,5-dimethylphenyl)- (S)-pyrrolidin-2-ylmethanol at reduced catalyst loading (20 mol %) with ees up to 94% for chalcone epoxides under mild reaction conditions, whereas (S)-diphenyl- 2-pyrrolidinemethanol afforded a maximum ee of 80%. Interestingly, the methodology is applicable to the epoxidation of more challenging aliphatic or enolizable enones with good control of the asymmetric induction (up to 87% ee).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
