Amino alcohol zinc complex

The slow nucleophilic addition of dialkylzinc reagents to aldehydes can be accelerated by chiral amino alcohols, producing secondary alcohols of high enantiomeric purity. The catalysis and stereochemistry can be interpreted satisfactorily in terms of a six-membered cyclic transition state assembly [46,47], In the absence of amino alcohol, dialkylzincs and benzaldehyde have weak donor-acceptor-type interactions. When amino alcohol and dialkylzinc are mixed, the zinc atom acts as a Lewis acid and activates the carbonyl of the aldehyde. Zinc in this amino alcohol-zinc complex is regarded as a kind of chirally modified Lewis acid. Various kinds of polymer-supported chiral amino alcohol have recently been prepared and used as ligands in dialkylzinc alkylation of aldehydes. 

TMS acetylene has been added to aromatic aldehydes in high ee, using an amino alcohol/zinc complex derived from prolinol. ... 

A substantial enhancement of the condensation rate of these substances is observed by using hydrotropes such as sodium butylmonoglycosulfate (NaBMGS) and the sodium salts of aromatic sulfonic acids in alkaline media [8]. In the absence of NaOH, the reaction does not proceed, which indicates that the hydrotropes do not catalyze the reaction and that the effect is simply that of the solubilization of the reactants at higher concentrations. The selectivity of the reaction of p-nitrobenzaldehyde with acetone can be controlled in aqueous media by working in the presence of zinc nitrate hexahydrate and A,A-dimethylaminoethanol [9]. The amino alcohol-zinc combination favors aldol addition at pH 9.1-9.5 and aldol condensation at pH 11.4. The same reaction catalyzed by metal complexes bearing ligands of the a-amino acids... 

Activators. Activators are chemicals that increase the rate of vulcanization by reacting first with the accelerators to form mbber soluble complexes. These complexes then react with the sulfur to achieve vulcanization. The most common activators are combinations of zinc oxide and stearic acid. Other metal oxides have been used for specific purposes, ie, lead, cadmium, etc, and other fatty acids used include lauric, oleic, and propionic acids. Soluble zinc salts of fatty acid such as zinc 2-ethyIhexanoate are also used, and these mbber-soluble activators are effective in natural mbber to produce low set, low creep compounds used in load-bearing appHcations. Weak amines and amino alcohols have also been used as activators in combination with the metal oxides. 

We came up with the idea of using a dummy ligand, as shown in Scheme 1.23 [34]. Reaction of dimethylzinc with our chiral modifier (amino-alcohol) 46 provided the methylzinc complex 62, which was subsequently reacted with 1 equiv of MeOH, to form chiral zinc alkoxide 63, generating a total of 2 moles of methane. Addition of lithium acetylide to 63 would generate an ate complex 64. The ate complex 64 should exist in equilibrium with the monomeric zincate 65 and the dimer 66. However, we expected that the monomer ate complex 64 and the mono-... 

A related enantiomerically pure zinc amide initiator, (340), has also been described.966 This complex catalyzes the alternating copolymerization of CHO and C02 to yield isotactic material (RR SS = 86 14). Similar enantiomeric excesses have been achieved using a mixture of Et2Zn and the chiral amino alcohol (341).967 Molecular weight distributions are much broader than using catalyst (340), but this protocol is still a convenient way to prepare optically pure diols (Scheme 23). 

High anti-diastereoselectivity is observed for several aromatic imines for ortho-substituted aromatic imines the two newly formed stereocenters are created with almost absolute stereocontrol. Aliphatic imines can also be used as substrates and the reaction is readily performed on the gram scale with as little as 0.25 mol% catalyst loading. Furthermore, the Mannich adducts are readily transformed to protected a-hydroxy-/8-amino acids in high yield. The absolute stereochemistry of the Mannich adducts revealed that Et2Zn-linked complex 3 affords Mannich and aldol adducts with the same absolute configuration (2 R). However, the diastereoselectiv-ity of the amino alcohol derivatives is anti, which is opposite to the syn-l,2-diol aldol products. Hence, the electrophiles approach the re face of the zinc enolate in the Mannich reactions and the si face in the aldol reactions. The anti selectivity is... 

Zinc complexes, consisting of amine, amino alcohol, alcohol, sulfide, or phosphine as ligand, catalyzed 1,4-addition of Grignard reagents to a,) -unsaturated carbonyl compounds [447,448]. An optically active ligand on zinc achieved asymmetric 1,4-addition, the best result is presented in Eq. (204) [448]. 

The addition of diethylzinc to aldehydes produces secondary alcohols. This process can be stereoselectively catalyzed by chiral amino alcohols that form Schiff-base zinc complexes with the aldehyde and the metal. With the aim of simplifying the work-up of these reactions and to use continuous-flow processes, the polymer-supported amino alcohols 115 and 116 were synthesized (Scheme 21) [91]. The polymers were obtained by co-polymerization of the chiral monomer 117 and styrene 58 in the presence of divinylbenzene (118) or cross-tinldng agent 119 containing a flexible oxyethylene chain. The latter was used to ensure sufficient flexibility within the cross-linked network of the polymer and to further activate the nucleophile by coordination of the oxyethylene chain to the metal. 

Zeise s salt, 353, 403 Zinc, 925-1022 metallocnzymcs, 1001, 1002 biomimetic modelling, 1021 X-ray crystallography, 1002 zinc-carbonyl mechanism, 1003 zinc-hydroxide mechanism. 1003 Zinc complexes acetate, 969 alcohols, 964 amides, 944 amine oxides, 964 amines, 933 amino acids, 938... 

Huang, X. Rickman, B.H. Borhan. B. Berova. N. Nakanishi. K. Zinc porphyrin tweezer in host-guest complexation—Determination of absolute configurations of diamines, amino acids, and amino alcohols by circular dichroism. J. Am. Chem. Soc. 1998. 120. 6158. 

Porphyrin tweezer 51 was used to determine the absolute configuration of chiral diamines by measuring the CD spectrum of the diamine-51 complex. - Upon com-plexation, the two porphyrins adopt a chiral configuration, which leads to a coupled CD. The absolute configuration of amino acids and amino alcohols can be similarly detennined after derivatization to diamines. Ji and coworkers also reported CD smdies of the binding of diamine to a zinc porphyrin dimer. ... 

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