Brønsted-Acid-Catalyzed Activation of Nitroalkanes: A Direct Enantioselective Aza-Henry Reaction
作者:Magnus Rueping、Andrey P. Antonchick
DOI:10.1021/ol8003589
日期:2008.5.1
A direct asymmetric organocatalytic aza-Henryreaction has been developed in which a new bifunctional Bronsted-acid-catalyzed activation of nitroalkanes provides an efficient access to alpha,beta-diamino acids with high dia- and enantioselectivities under mild and base-free reaction conditions.
Heterogeneous asymmetric nitro-Mannich reaction using a bis(oxazoline) ligand grafted on mesoporous silica
作者:Anna Lee、Woosung Kim、Jinwoo Lee、Taeghwan Hyeon、B. Moon Kim
DOI:10.1016/j.tetasy.2004.07.024
日期:2004.9
A chiral bis(oxazoline) ligand was immobilized on mesoporous silica (SBA-15) and examined in an asymmetric heterogeneous nitro-Mannich reaction. Depending upon the size of the alkyl chain in the nitroalkane substrates, enantioselectivities comparable to and higher diastereoselectivities (syn/anti ratio) than those obtained from homogeneous reactions were observed. In the case of the long chain substituted nitroalkane substrate (nitrohexane), the best selectivities (diastereoselectivity: syn/anti = 98/2, and enantioselectivity: 93% and 82% ee's for syn- and anti-isomers, respectively), were observed. Recycling of the catalyst in subsequent reactions was carried out and gradually diminishing levels of both diastereo and enantioselectivities were observed after each recycle. (C) 2004 Elsevier Ltd. All rights reserved.
The First Catalytic Asymmetric Aza-Henry Reaction of Nitronates with Imines: A Novel Approach to Optically Active β-Nitro-α-Amino Acid- and α,β-Diamino Acid Derivatives
作者:Kristian Rahbek Knudsen、Tine Risgaard、Nagatoshi Nishiwaki、Kurt V. Gothelf、Karl Anker Jørgensen