Effective and recyclable dendritic ligands for the enantioselective epoxidation of enones
摘要:
An operationally simple and mild protocol for the catalytic enantioselective epoxidation of enones has been established using a series of chiral pyrrolidinylmethanol-based dendritic catalysts and tert-butyl hydroperoxide (TBHP) as an oxidant. The epoxides have been obtained in good yields and ee up to 78%. (c) 2006 Published by Elsevier Ltd.
from l‐ and d‐xylose, and l‐ and d‐arabinose, respectively. These monosaccharide‐based chiral macrocycles were tested as phase transfer catalysts in a few asymmetric reactions. The xylal‐based crown compounds proved to be efficient catalysts in a few liquid‐liquid phase reactions. The epoxidation of trans‐chalcone and the Darzens condensation of α‐chloroacetophenone with benzaldehyde took place with
A highly efficient catalytic kinetic resolution of 2,3-epoxy 3-aryl ketones via asymmetric ring-opening with pyrazole derivatives has been achieved by using a chiral N,N′-dioxide–Sc(iii) complex as the catalyst.
Asymmetric C–C bond formation via Darzens condensation and Michael addition using monosaccharide-based chiral crown ethers
作者:Péter Bakó、Zsolt Rapi、György Keglevich、Tamás Szabó、Péter L. Sóti、Tamás Vígh、Alajos Grűn、Tamás Holczbauer
DOI:10.1016/j.tetlet.2011.01.094
日期:2011.3
phase asymmetric Darzens condensations were promoted by d-glucose- and d-mannose-based crown ethers. The corresponding aromatic and heteroaromatic α,β-epoxyketones were obtained with moderate to high enantioselectivities (up to 96%) as well as diastereoselectivities (up to 98:2) under mild reaction conditions. The absolute configurations of several of the epoxyketones were determined by single crystal
and d-mannose-based crown ethers 1 and 2 as the catalyst. The use of d-glucose-based lariat ether 1 as the catalyst gave the best results. The reaction of 4-phenyl-α-chloroacetophenone, 2-chloro-1-tetralone, and 2-chloro-1-indanone with various aromatic aldehydes afforded the corresponding aromatic α,β-epoxyketones in moderate to high enantiomeric excess (ee up to 96%) under mild reaction conditions
An operationally simple and mild protocol for the catalytic enantioselective epoxidation of enones has been established using a series of chiral pyrrolidinylmethanol-based dendritic catalysts and tert-butyl hydroperoxide (TBHP) as an oxidant. The epoxides have been obtained in good yields and ee up to 78%. (c) 2006 Published by Elsevier Ltd.