Asymmetric Addition Of Diethylzinc Research Articles

Ligand Anatomy: Probing Remote Substituent Effects in Asymmetric Catalysis through NMR and Kinetic Analysis

A series of structurally related beta-amino alcohols only differing in the steric bulk of a remote alkoxy group exhibit striking differences in kinetic behavior when used as ligands in the asymmetric diethylzinc addition to benzaldehyde (R = Trityl, much more active). A combination of NMR titration studies and kinetic analysis allows the quantitative decomposition of the remote substituent effect into a lower dimerization constant of the active species and a much faster ethyl addition step.

Synthesis of Chiral C/N‐Functionalized Morpholine Alcohols: Study of Their Catalytic Ability as Ligand in Asymmetric Diethylzinc Addition to Aldehyde.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Asymmetric addition of diethylzinc to benzaldehyde catalyzed by silica-immobilized titanium(IV) complexes of N-sulfonylated amino alcohols

A chiral (1 R,2 S)-2-( p-toluenesulfonylamino)-1,3-diphenyl-1-propanol derived catalyst was synthesized and successfully grafted onto amorphous silica gel and mesoporous silica (MCM-41) by a facile approach. This is the first use of silica-immobilized titanium(IV) complexes of N-sulfonylated amino alcohols for the asymmetric addition of diethylzinc to benzaldehyde with good enantioselectivity (80% e.e.). Particularly, after readily recoverble procedure, the catalyst was able to be reused in multiple catalytic runs (up to 10 times) without loss of enantioselectivity.

A Facile Synthesis of 3‐ or 3,3′‐Substituted Binaphthols and Their Applications in the Asymmetric Addition of Diethylzinc to Aldehydes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis of modified H 4-BINOL ligands and their applications in the asymmetric addition of diethylzinc to aromatic aldehydes

Two new ligands ( S, S)-3-(1,1′-bi-2-naphthol-3-yl)-5,6,7,8-tetrahydro-1,1′-bi-2-naphthol [( S, S)- 1] and ( S)-3-(morpholin-4-ylmethyl)-H 4-BINOL [( S)- 2] have been synthesized via Suzuki cross-coupling reaction and a Mannich-type reaction, respectively. In the presence of titanium tetraisopropoxide, 0.8 mol % of ligand ( S, S)- 1 catalyzed the asymmetric addition of diethylzinc to aromatic aldehydes in good yield and with high enantioselectivity.

Design and Synthesis of 1,4-Amino Alcohol Ligands with a Chiral Cyclopropane Backbone for Asymmetric Diethylzinc Addition to Aromatic Aldehydes

A new type of cis-1,4-amino alcohols with a cyclopropane backbone have been developed in three simple steps, from a cheap industrial intermediate for enantioselective asymmetric diethylzinc addition to aromatic aldehydes, under mild conditions to afford corresponding secondary alcohols in high yield with excellent enantioselectivity.

Calculation on enantiomeric excess of catalytic asymmetric reactions of diethylzinc addition to aldehydes with topological indices and artificial neural network

The relationships between the enantiomeric excess of products in several types of asymmetric diethylzinc addition reactions and the structures of the catalysts and reagents were studied by using the BP neural network with topological indices. Moderate cross-validated correlation coefficients were yielded by the models generated from the neural network. Then the models were further used to validate reaction mechanisms, determine the proper reaction environment, and predict the activities of new catalysts.

Novel C2‐Symmetric 1,1′‐Disubstituted Ferrocenyl Aziridino Alcohol Ligands: Remarkable Improvement of Enantioselectivity in the Catalytic Asymmetric Addition of Diethylzinc to Aldehydes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Convenient synthesis of a new class of chiral hydroxymethyldihydrooxazole ligands and their application in asymmetric addition of diethylzinc to aromatic aldehydes

A number of chiral hydroxymethyl-substituted dihydrooxazoles were synthesized from D-or L-mandelic acid and amino alcohols. The chiral ligands thus obtained were tested as catalyst in the asymmetric addition of diethylzinc to aromatic aldehydes, and the structure-activity relationship was studied. The addition products were characterized by an enantiomeric excess of up to 91%.

Synthesis of 3 or 3,3′‐Substituted BINOL Ligands and Their Application in the Asymmetric Addition of Diethylzinc to Aromatic Aldehydes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis and Application of 3,3′-Diarylmethyl BINOLs

A new class of 3,3′-diarylmethyl BINOL derivatives were synthesized and applied to the catalytic asymmetric addition of diethylzinc to aldehydes. These chiral diol auxiliaries could be used as catalysts without the addition of Ti(i-PrO)4 and showed unprecedented catalytic activities and enantioselectivities (up to 94% ee, 5 mol% catalyst loading).

P‐Chiral o‐Phosphinophenol as a P/O Hybrid Ligand: Preparation and Use in Cu‐Catalyzed Asymmetric Conjugate Addition of Diethylzinc to Acyclic Enones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis of New Chiral [2‐(1‐Hydroxyalkyl)pyrrolidino]methylferrocenes and Application to the Catalytic Asymmetric Addition of Diethylzinc to Arylaldehydes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Synthesis of chiral C/N-functionalized morpholine alcohols: study of their catalytic ability as ligand in asymmetric diethylzinc addition to aldehyde

A broad variety of chiral C/N-functionalized morpholine alcohols sharing a common structural motif in the 3-(hydroxymethyl)morpholine 6 were prepared from enantiomerically pure serine for the purpose of studying their catalytic ligand properties. The asymmetric addition of diethylzinc to benzaldehyde in the presence of 10 mol % of chiral C/N-functionalized morpholine alcohols gave 1-phenyl-1-propanol in 59–81% yield with 10–30% ee. The addition of 10 mol % of n-butyl lithium to the reaction mixture resulted in a significant enhancement of the stereoselectivity in the case of ligands bearing the two geminal phenyl substituents on the backbone. In the presence of n-butyl lithium and using ( S)-3-(hydroxydiphenylmethyl)morpholine ( S)- 19 as the chiral promoter, ( S)-1-phenyl-1-propanol was obtained in 81% yield with 76% ee. The geminal diphenyl-class of morpholine ligands was examined for the diethylzinc addition to four different aldehydes in the presence of n-butyl lithium. ( S)- N-Benzyl-3-(hydroxydiphenylmethyl)morpholine ( S)- 27 was found to be most enantioselective in the case of 4-methoxybenzaldehyde to give ( R)-alcohol in 87% yield with 80% ee. Catalysts ( S)- 19 and its N-methyl derivative ( S)- 26 gave alcohols with an ( S)-absolute configuration while the N-benzylated derivative ( S)- 27 gave the opposite enantiomeric products. The tentative transition state models to account for the observed product stereoselectivity with morpholine ligands holding the geminal diphenyl group on the β-amino alcohol segment are proposed.

A facile synthesis of 3 or 3,3′-substituted binaphthols and their applications in the asymmetric addition of diethylzinc to aldehydes

By using a direct ortho-lithiation, the ligands ( S)-3-methoxymethyl-1,1′-bi-2-naphthol [( S)- 1], ( S)-3,3′-bis(methoxymethyl)-1,1′-bi-2-naphthol [( S)- 2], ( S)-3-(quinolin-2-yl)-1,1′-bi-2-naphthol [( S)- 3] and ( S)-3,3′-bis(quinolin-2-yl)-1,1′-bi-2-naphthol [( S)- 4] have been synthesized. ( S)- 1 and ( S)- 3 show moderate catalytic properties for the asymmetric diethylzinc addition to aromatic aldehydes.

Chiral N-heterocyclic carbene ligands based on a biisoquinoline template

New chiral imidazolinium salts with tunable steric features, based on a biisoquinoline template, have been developed and structurally characterised using single crystal X-ray crystallography. The trans PdI(2)(NHC)(2) complex was prepared by reaction of the parent H(4) imidazolinium salt with Pd(OAc)(2) in the presence of NaI, and the solid state structure determined by X-ray crystallography. The rigid, chiral, biisoquinoline geometry of the H(4) imidazolinium salt was found to be maintained upon ligand complexation. The sterically unencumbered parent biisoquinoline ligand has been found to give high conversion with modest enantioselectivity in the copper-catalysed asymmetric addition of diethylzinc to cyclohexenone.

Immobilization of a BINOLate-Titanium Catalyst by Use of Aggregation Phenomenon

Upon treatment with titanium tetraisopropoxide, tris-BINOL with a rigid aromatic tether forms an insoluble polymeric aggregate, which shows a catalytic activity in asymmetric addition of diethylzinc to aldehydes.

Discovery of Chiral Catalysts by Asymmetric Activation for Highly Enantioselective Diethylzinc Addition to Imines: Using Racemic and Achiral Diimines as Effective Activators.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Novel Chiral Copper Complexes of N,P‐Ferrocenyl Ligands with Central and Planar Chirality as Efficient Catalyst for Asymmetric Addition of Diethylzinc to Imines.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mesoporous Silica SBA-15-supported Norephedrine and Ephedrine as Heterogeneous Chiral Ligands

Successful development of the homogeneous catalysts has been sometimes followed by attempts to attach the catalysts on an insoluble polymeric support. A suitably designed immobilized catalyst can retain the advantages of a heterogeneous catalyst in terms of simplified workup procedure and recyclization while maintaining reactivity and selectivity of a homogeneous catalyst. The immobilization of homogeneous species is of particular interest in the field of asymmetric catalysis since it is desirable to be able to regenerate and reuse expensive chiral catalysts. Polystyrene resin and silica gel have been most commonly used as insoluable supports for the immobilization of the catalysts. Recently, mesoporous silica SBA-15 with large uniform pore diameters and high specific surface areas have become of high interest as inorganic supports. Our interest in the field led to prepare SBA-15-supported ephedrine 1 and norephedrine 2. Herein, we report our investigation on the asymmetric addition of diethylzinc reagent to aldehydes and on the asymmetric transfer hydrogenation of ketones mediated by the supported ligands. As shown in Scheme 1, (−)-ephedrine was anchored on SBA-15 silica in a similar procedure as for silica gelsupported ephedrine 1. Treatment of SBA-15 with an excess of (3-chloropropyl)triethoxysilane in refluxing toluene gave chloropropylated SBA-15. The free silanol group was endcapped by treatment with hexamethyldisilazane (HMDS). Reaction of the samples are summarized in Table 1. The surface area was decreased considerably in the chloropropylation, but the pore diameter was not changed substantially during the modification steps. chloropropylated SBA-15 with 1.5 equiv. excess of (−)-ephedrine in refluxing toluene in the presence of 1 equiv of diisopropylethylamine afforded SBA-15-supported ephedrine 1. SBA-15-supported norephedrine 2 was also prepared from (−)-norephedrine by the same method. The degrees of functionalization were determined by weight gain or nitogen elemental analysis for the modified SBA-15. The characteristics of the two samples are summarized in Table 1. The surface area was decreased considerably during the modification, but the pore diameter was not changed substantially. With the supported ephedrine 1 in hand, we examined its catalytic efficiency in asymmetric addition of diethylzinc to aldehyde in hexane. Aldehydes were converted to the corresponding (R)-secondary alcohols with moderate ee's in high yields. The results were compared to the data previously obtained with amorphrous silica gel-supported ephedrine. As can be seen in Table 2, SBA-supported ephedrine 1 gave much higher reaction rate and better