Enantioselective cyanation of aldehydes catalyzed by bifunctional salen–aluminum complex
摘要:
Chiral N-oxide salen ligands and their corresponding Al complexes were synthesized. Notably, the catalytic activity and asymmetric induction ability of the bifunctional N-oxide salen-Al for asymmetric cyanosilylation were compared with that of bi-component catalyst system including chiral pyrrolidine salen-Al complex and Ph3PO. Interestingly, introducing N-oxide group in salen unit could enhance the activity and enantioselectivity of bifunctional catalyst without further adding Ph3PO as co-catalyst and inverse configurations were generated from the two systems. In addition, excellent yields and high ee values could be obtained under milder conditions in bifunctional catalyst system compared with that of bi-component catalyst system. (C) 2012 Elsevier B.V. All rights reserved.
Kinetics and mechanism of vanadium catalysed asymmetric cyanohydrin synthesis in propylene carbonate
作者:Michael North、Marta Omedes-Pujol
DOI:10.3762/bjoc.6.119
日期:——
Propylene carbonate can be used as a green solvent for the asymmetricsynthesis of cyanohydrin trimethylsilyl ethers from aldehydes and trimethylsilyl cyanide catalysed by VO(salen)NCS, though reactions are slower in this solvent than the corresponding reactions carried out in dichloromethane. A mechanistic study has been undertaken, comparing the catalytic activity of VO(salen)NCS in propylene carbonate
The Asymmetric Addition of Trimethylsilyl Cyanide to Aldehydes Catalyzed by Chiral (Salen)Titanium Complexes
作者:Yuri N. Belokon'、Susana Caveda-Cepas、Brendan Green、Nicolai S. Ikonnikov、Viktor N. Khrustalev、Vladimir S. Larichev、Margarita A. Moscalenko、Michael North、Charles Orizu、Vitali I. Tararov、Michela Tasinazzo、Galina I. Timofeeva、Lidia V. Yashkina
DOI:10.1021/ja984197v
日期:1999.4.1
The use of chiral (salen)TiCl2 complexes to induce the asymmetricaddition of trimethylsilyl cyanide to aldehydes has been investigated. The complexes are catalytically active at substrate-to-catalyst ratios as high as 1000:1, and the optimal catalyst (2e) which is derived from (R,R)-1,2-diaminocyclohexane and 3,5-di-tert-butyl-2-hydroxybenzaldehyde produces trimethylsilyl ethers of cyanohydrins with
Asymmetric catalysis of carbon–carbon bond forming reactions using amino acid-derived C1-symmetrical salen ligands
作者:Yuri N. Belokon′、Jamie Hunt、Michael North
DOI:10.1016/j.tetasy.2008.11.037
日期:2008.12
Four amino acids (alanine, valine, phenylalanine and phenylglycine) have been converted into C1-symmetrical salen ligands and complexed to titanium, vanadium, copper and cobalt. The resulting complexes have been used as asymmetric catalysts for asymmetric cyanohydrin synthesis, asymmetric Strecker reactions, asymmetricsynthesis of α-methyl amino acids and asymmetric Darzens condensations. Satisfactory
Fine Modification of Salen Ligands - Effects on the Salen-Ti-Catalyzed Asymmetric Cyanosilylation of Aldehydes
作者:Chengwei Lv、Qigan Cheng、Daqian Xu、Shoufeng Wang、Chungu Xia、Wei Sun
DOI:10.1002/ejoc.201100319
日期:2011.7
bifunctional N-oxide salen―Ti IV complexes and a pyrrolidine salen―Ti IV complex in combination with achiral N-oxide were developed and applied to the asymmetricaddition of trimethylsilyl cyanide to aldehydes. Notably, both enantiomers of trimethylsilyl ethers of cyanohydrins could be easily prepared by modifying the catalysts employed in this reaction, which are based on the same chiral diamine collar
开发了新的双功能 N-氧化物 salen-Ti IV 配合物和吡咯烷 salen-Ti IV 配合物与非手性 N-氧化物的结合,并将其应用于三甲基氰基氰化物与醛的不对称加成。值得注意的是,氰醇的三甲基甲硅烷基醚的两种对映异构体都可以通过修改该反应中使用的催化剂来轻松制备,这些催化剂基于相同的手性二胺环,源自 L-酒石酸。通过使用相对低的催化剂负载量和仅 1.05 当量的三甲基氰基氰化物 (TMSCN),通常以中等至良好的对映体过量和优异的产率获得产物。
A practical Ti-salen catalyst based on dimeric salen ligand for asymmetric addition of trimethylsilyl cyanide to aldehydes
作者:Chengwei Lv、Daqian Xu、Shoufeng Wang、Cheng-Xia Miao、Chungu Xia、Wei Sun
DOI:10.1016/j.catcom.2011.04.022
日期:2011.7
from L-tartaric acid was synthesized through linking two salen units with 1,6-dibromohexane. The corresponding Ti complex was proved to be an efficient catalyst for asymmetric addition of trimethylsilyl cyanide to aldehydes, providing the corresponding optically active trimethylsilyl ether of cyanohydrins with moderate to good enantiomeric excesses and excellent yields under relatively low catalyst