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.
Catalytic Asymmetric Insertion of Diazoesters into Aryl-CHO Bonds: Highly Enantioselective Construction of Chiral All-Carbon Quaternary Centers
作者:Lizhu Gao、Byung Chul Kang、Do Hyun Ryu
DOI:10.1021/ja408196g
日期:2013.10.2
This paper describes a catalytic enantioselective route to synthesize functionalized all-carbonquaternary acyclic systems via a boron Lewis acid-promoted formal C-C insertion of diazoesters into aryl-CHO bonds. In the presence of chiral (S)-oxazaborolidinium cation 1d as a catalyst, the reaction proceeded in good yield (up to 83%) with good regioselectivity (up to 88:12) and excellent enantioselectivity
Catalytic enantioselective 1,3-dipolar cycloadditions of alkyl diazoacetates with α,β-disubstituted acroleins
作者:Lizhu Gao、Geum-Sook Hwang、Mi Young Lee、Do Hyun Ryu
DOI:10.1039/b910321j
日期:——
A catalytic route to highly functionalized chiral 2-pyrazolines by an asymmetric 1,3-dipolar cycloaddition reaction of ethyl diazoacetate with α-substituted and α,β-disubstituted acroleins has been developed; in the presence of chiral (S)-oxazaborolidinium ion 1 as catalyst, the reaction proceeded with high to excellent enantioselectivities (up to 99% ee).
Chiral oxazaborolidinium ion-catalyzed asymmetric cyclopropanation of α- or α,β-substituted acroleins with α-alkyl-α-diazoesters has been developed. With this methodology, chiral functionalized cyclopropanes containing a quaternary stereogenic center were obtained with high to excellent enantioselectivities (up to >99% ee). The synthetic utility of optically enriched functionalized cyclopropane was