Asymmetric transfer hydrogenations of β-N-substituted enamino esters with ammonia borane
作者:Weiwei Zhao、Xiangqing Feng、Jing Yang、Haifeng Du
DOI:10.1016/j.tetlet.2019.03.060
日期:2019.4
β-enamino esters is one of the most efficientapproaches for their synthesis. Ammonia borane with low molecular weight, high hydrogen capacity, and good stability, is an ideal hydrogen source for the transfer hydrogenation. However, only a few successful examples have been reported for the asymmetric reduction with ammonia borane. In this work, an asymmetric metal-free transfer hydrogenation of β-N-substituted
Synthesis of chiral β-amino acid derivatives by asymmetric hydrosilylation with an imidazole derived organocatalyst
作者:Simon Jones、Xianfu Li
DOI:10.1016/j.tet.2012.04.084
日期:2012.7
hydrosilylation of a number of N-aryl and alkyl β-substituted enamino esters proceeds in generally good yield and enantioselectivity. Crucial to obtaining high yield and selectivity was the addition of benzoic acid as an additive and under these conditions, both N-alkyl and N-aryl substituents were well tolerated. β-Aryl and alkyl substituents were evaluated and a model proposed to account for the experimental
The mixtures of axiallychiral (aR,S)- and (aS,S)-biscarboline alcohols were firstly used as catalysts in enantioselective 1,2- and 1,4-transfer hydrogenations of ketimines and β-enamino esters, respectively. This mixed axiallychiral catalysts exhibited excellent enantioselectivity (up to 98%ee) in the transfer hydrogenations under mild reaction conditions.
A Continuously Regenerable Chiral Ammonia Borane for Asymmetric Transfer Hydrogenations
作者:Qiwen Zhou、Wei Meng、Jing Yang、Haifeng Du
DOI:10.1002/anie.201806877
日期:2018.9.10
A novel chiral ammonia borane was designed and developed through the dehydrogenation of ammonia borane with a chiral phosphoric acid, which was highly effective for the asymmetric transfer hydrogenation of imines and β‐enamino esters to afford high levels of reactivities and enantioselectivities. Significantly, this chiral ammonia borane can be continuously regenerated during the transfer hydrogenation
aminoacid after dehydrogenation and oxidations using m-CPBA. These diastereoisomers can be obtained by column chromatography and used as catalysts in asymmetric hydrogenation reactions of β-enamine esters and ketimines. Chiral catalysts 6 and 7 exhibited very high enantioselectivity in the reactions. For example, high up to 98%ee was achieved in the enantioselective hydrogenations when only 1%mol of