Ligands chiral amino alcohol-based

Jiang et al. utilized inexpensive chiral amino alcohol-based ligand, dimethylamino-l(p-nitrophenyl)-3-(ferf-butyldimethylsilyloxy)propane-l-ol for asymmetric alkylation of both aliphatic and aromatic aldehydes upto 99% e.e. Other ligands were also tested for this transformation (aminols 1 to 4, Scheme 21.17). 

A combination of the Lewis acid zinc triflate and the bases NEt, or pyridine acted as an achiral catalyst for this reaction. Instead, using a chiral base which incorporates a bipy ligand to bind zinc gave 26% ee of the product (Scheme 5-42a). Alternatively, diethylzinc was an active precatalyst, but attempts to use chiral amino alcohols as ligands in this system gave low ees (Scheme 5-42b) [31]. 

Figure 6.11 Typical tridentate ligand structure incorporating a chiral amino alcohol and modified diamine-based tridentate ligand structure attached to the solid support for parallel catalyst library strategy.

The above azomethine ylide cycloadditions have been extended to an enantioselective version involving amino alcohols both as chiral ligands and amine bases. Thus, reactions of the N-metalated azomethine yhdes derived from achiral methyl 2-(arylmethyleneamino)acetates, cobalt(II) chloride [or manganese(II) bromide], and chiral amino alcohols, 1 and 2 equiv each, with methyl acrylate as solvent have been performed to provide the enantiomer-enriched pyrrolidine-2,4-dicarboxylates with the enantioselectivities of up to 96% enantiomeric excess (ee) (128,129). However, a large excess of the metal ions and the chiral source (ligand and base) have to be employed. 

Boron enolates bearing menthol-derived chiral ligands have been found to exhibit excellent diastereo- and enantio-control on reaction with aldehydes34 and imines.35 Highly diastereo- and enantio-selective aldol additions of geometrically defined trichlorosilyl ketone enolates (31) and (32) have been achieved by promoting the reactions with chiral Lewis bases, of which (S,S)-(33) proved to be the most effective.36 Moderate enantiomeric excesses have been achieved by using chiral amino alcohols as catalysts for the Baylis-Hillman condensation of aldehydes with methyl vinyl ketone the unexpected pressure effect on the reaction has been rationalized.37... 

The indium-induced Reformatsky reaction with stoichiometric amounts of chiral amino alcohols such as cinnco-nine and cinchonidine gives optically active /3-hydroxy esters with 40%-70% ee (Table 19). In contrast to the smooth reaction with uncomplexed indium-based Reformatsky reagents, ketones do not react with the complexed indium Reformatsky reagents. Other chiral ligands, including (—)-spartein, (—)-norephedrine, (+)-(l-methylpyrrolidin-2-yl)diphenylmethanol, (+)-Dibutyl tartrate and (+)-l,l -bi-2-naphthol, are not effective for this reaction.324... 

A new family of hybrid organic-inorganic catalysts with dispersed active sites inside ordered mesoporous materials has been prepared by anchorage of transition-metal ligands of Schiff base-type and chiral amino alcohols like (li ,2S)-ephedrine on micelle-templated silicas [180]. Metalation of the grafted ligands with manganese was followed by UV-VIS spectroscopy. 

A few publications deal with silicon complexes of chiral 0,N,0-ligands. Tridentate imine ligands were obtained from chiral amino alcohols by Schlecht et al. [278]. These ligands serve for the formation of bis-chelated silicon complexes. Whereas the complex based on 2-amino-l,L2-triphenylethanol is obtained as a diastereomeric... 

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