A new chiral Brønsted acid derived from carboxylic acid and a chiral oxazaborolidinium ion (COBI), as an activator, is introduced. This acid was successfully applied as a catalyst for the highly enantioselective protonation/nucleophilicaddition of diazoesters with carboxylic acids.
Desymmetrizing Asymmetric Ring Expansion of Cyclohexanones with α-Diazoacetates Catalyzed by Chiral Aluminum Lewis Acid
作者:Takuya Hashimoto、Yuki Naganawa、Keiji Maruoka
DOI:10.1021/ja202070j
日期:2011.6.15
in a 2:1 ratio was found to promote novel catalytic asymmetric ring expansion of cyclohexanone with α-substituted α-diazoacetates to give seven-membered rings with an all-carbon quaternary center. Application of this strategy to 4-substituted cyclohexanones opened up a novel way for the catalytic desymmetrizing asymmetric construction of cycloheptanones bearing remote α,δ-chiral centers.
Enantioselectivecyclopropanation and C–H insertion reactions of α-substituted vinyl ketones with α-diazoesters have been accomplished using a N,N′-dioxide-scandium(III) complex catalyst. Various tetrasubstituted cyclopropanes and E-enone derivatives bearing a chiral ester substituent were obtained simultaneously with good yields and excellent enantioselectivities.