Enantioselective Alkylation Of Benzaldehyde Research Articles

Enantioselective alkylation of aromatic aldehydes with (+)-camphoric acid derived chiral 1,3-diamine ligands

A series of chiral 1,3-diamine ligands derived from (+)-camphoric acid were prepared from the reaction of 1,3-diamino-1,2,2-trimethylcyclopentane with aromatic aldehydes, followed by reduction of the corresponding diimines. These newly synthesized ligands were tested in the enantioselective alkylation of benzaldehyde with diethylzinc, giving 1-phenyl-1-propanol with enantiomeric ratios of up to 86:14. Our most selective ligand, derived from 2-methoxybenzaldehyde, was also tested in the alkylation of several aromatic aldehydes and product alcohols with enantiomeric ratios of up to 93.5:6.5 being observed in 2h at room temperature in the presence of 5mol% ligand.

Stereoselective syntheses of pinane-based 1,3-diamines and their application as chiral ligands in the enantioselective addition of diethylzinc to benzaldehyde

A library of 1,3-difunctionalized pinane derivatives was synthesized and applied as chiral catalysts in the addition of diethylzinc to benzaldehyde. The key intermediate β-lactam 2 was prepared regio- and stereoselectively from (−)-apopinene 1. The treatment of 2 with di-tert-butyl dicarbonate afforded N-Boc β-lactam 3, while acid-catalyzed ring opening of 2 resulted in amino acid 4. Nucleophilic ring opening of 3 with dimethylamine, followed by deprotection and benzylation, furnished β-amino amides 5, 8, and 11, which were transformed in two steps into the corresponding N-tosyldiamines 7, 10, and 13, respectively. Since the use of other amines, such as diethylamine, to study the influence of dialkyl substitution was unsuccessful, an alternative synthetic route was applied. Amidation of tosylated β-amino acid 14 furnished amides 15–25. Reduction of 15, 16, 19, 20, and 24 resulted in N-tosyl diamines 26–30. The β-amino amides and N-tosylated diamines were used as chiral ligands in the enantioselective alkylation of benzaldehyde with diethylzinc, resulting in (R)- and (S)-1-phenyl-1-propanol. The (R)-enantiomer was predominant except when 17, 22, 23, and 25 were used as ligands, in which case the opposite stereochemistry was observed. The best ee values (up to 83%) were obtained when 17, 20, 23, and 25 were used as catalysts.

ChemInform Abstract: Chiral Diethanolamines and Their Lithium Alcoholates as Catalysts in the Enantioselective Alkylation of Benzaldehyde by Diethylzinc.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Catalytic investigation of (1R,2S)-(−)-N-dodecyl-N-methylephedrinium bromide immobilized on montmorillonite in the enantioselective alkylation of benzaldehyde with diethylzinc

Abstract The optically active cationic surfactant (1 R ,2 S )-(−)- N -dodecyl- N -methylephedrinium bromide (DMEB) was immobilized on montmorillonite (M) via cation exchange. XRD studies revealed that the resulting hydrophobic clay organocomplex dodecylmethylephedrinium–montmorillonite (DME–M) underwent a pronounced swelling in ethanol, tetrahydrofuran and toluene. The catalytic behaviour of the heterogenized surfactant was investigated for the enantioselective addition of diethylzinc to benzaldehyde and the results were compared with those obtained for DMEB in a homogeneous reaction, under otherwise the same conditions. The utilization of both DMEB and DME–M afforded pronounced selectivities for the formation of 1-phenyl-1-propanol. The application of DME–M was found to result in higher conversions and lower enantioselectivities than those observed for DMEB. The effect of the reaction temperature on the catalytic behaviour of the pristine and immobilized chiral surfactant was also examined.

Approach to a better understanding and modelling of β-pyrrolidinoalcohol ligands for enantioselective alkylation

A series of pyrrolidine-based β-amino alcohols derived from malic acid, citramalic acid and pantolactone with primary amines was prepared and their activity as chiral ligands in the enantioselective alkylation of benzaldehyde using diethylzinc was studied.

Synthesis of chiral pentacyclo-undecane ligands and their use in the enantioselective alkylation of benzaldehyde with diethylzinc

The synthesis of a new class of chiral pentacycloundecane cage annulated bidentate ligands is reported. This class of ligands can be used in many reactions that are catalysed by amino alcohol ligands. The ability of the chiral ligands to asymmetrically catalyse the reaction between diethylzinc and benzaldehyde was investigated. The cage annulated bidentate ligands have C 1 symmetry and showed poor to good enantioselectivity with high yields compared to previous systems reported using other amino alcohol ligands. An important conclusion from the results is that both ligands should be involved in the mechanism as the bidentate ligands gives much improved enantioselectivity when compared with a single chiral source molecule. This system could be utilised as a versatile probe for examining the reaction mechanism.

ChemInform Abstract: Chiral Tridentate versus Bidentate Pyridines as Catalysts in the Enantioselective Alkylation of Benzaldehyde with Diethylzinc.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Enantioselective Alkylation of Benzaldehyde with Diethylzinc Catalyzed by 1,1′‐ and 1,2‐Disubstituted Ferrocenyl Amino Alcohols.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Design of mesoporous aluminosilicates supported (1 R,2 S)-(−)-ephedrine: evidence for the main factors influencing catalytic activity in the enantioselective alkylation of benzaldehyde with diethylzinc

(−)-Ephedrine, used as a model β-amino alcohol, was covalently anchored on mesoporous micelle templated aluminosilicates (Al-MTS) through nucleophilic substitution of halogenoalkyl(aryl)silane chains previously grafted on the surface. The covalent grafting was performed either by silylation (method a) or by surface sol–gel (method b). The latter method provided higher loading. However, the higher loading lowers the resulting mesoporous volume. The coupling alkyl halide moiety was then substituted with (1 R,2 S)-(−)-ephedrine. Used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc, these materials showed properties which depend mainly on the grafting method. The best results (activity, enantioselectivity) were obtained with catalysts prepared from supports featuring high initial pore diameter. The effect of the regular porosity on the efficiency and enantioselectivity was shown. Dilution of catalytic sites by alkyl groups and rigidification of the linker were also studied.

Chiral tridentate versus bidentate pyridines as catalysts in the enantioselective alkylation of benzaldehyde with diethylzinc

Comparison of the enantioselectivity obtained with either bidentate or tridentate chiral pyridine derivatives demonstrated that both can be very efficient catalysts for the enantioselective addition of diethylzinc to benzaldehyde. This comparison also provided insights for the design of efficient new catalysts based on pyridine.

Enantioselective alkylation of benzaldehyde with diethylzinc catalyzed by 1,1′- and 1,2-disubstituted ferrocenyl amino alcohols

Optically active 1,1′- and 1,2-disubstituted ferrocenyl amino alcohols have been synthesized from 1,1′- and 1,2-ferrocene dicarboxaldehyde. They have been used as chiral catalysts in the asymmetric addition of diethylzinc to benzaldehyde. 1-Phenylpropanol has been obtained in up to 83% enantiomeric excess.

Heterogeneous enantioselective carbon–carbon bond formation: role of the inorganic support in the synthesis and activity of supported chiral auxiliaries

Heterogeneous enantioselective alkylation of benzaldehyde with diethylzinc was performed using (-)-ephedrine grafted on mesoporous micelle templated aluminosilicates or silicates, as chiral auxiliary. Supports were characterized by a regular mesoporosity and a same initial pore diameter. Immobilization of the chiral aminoalcohol was performed through covalent anchoring of 3-halogenopropyltrimethoxysilane (XPTMS) and substitution of the halogen by (-)-ephedrine. Comparison of the efficiency of the catalysts was carried out. Results were analyzed taking into account the accessibility to the catalytic sites by changing their density (decrease of XPTMS concentration, spacing of the sites by alkyl goups) and the effect of the uncovered mineral surface on activities and enantioselectivities.

Factors affecting the efficiency of hybrid chiral mesoporous silicas used as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

Chiral hybrid organic–inorganic materials were prepared by anchoring optically active β-aminoalcohols such as (−)-ephedrine on MCM-41 type silica as a member of micelle-templated silicas (MTS). Silylation of the surface was performed with halogenopropyltrimethoxysilane. Then, (−)-ephedrine was anchored through halogen substitution. These materials were used as chiral auxiliaries in the heterogeneous enantioselective catalysis of the alkylation of benzaldehyde by diethylzinc. This work deals with the study of the various factors such as accessibility to the catalytic sites and coverage of the inorganic surface, which affect their efficiency (activity, selectivity and enantioselectivity).

Chiral mesoporous templated silicas as heterogeneous inorganic–organic catalysts in the enantioselective alkylation of benzaldehyde

New mesoporous templated silicas of the MCM-41 family covalently linked to chiral ephedrine are used as heterogeneous chiral auxiliaries in the enantioselective alkylation of benzaldehyde by diethylzinc. Promising results are obtained with these inorganic–organic catalysts. Various factors which may affect the activity, selectivity and enantioselectivity are studied. Comparison with homogeneous catalysis is carried out.

Enantioselective addition of diethylzinc to benzaldehyde catalyzed by chiral titanate complexes with helical ligands

Abstract Enantioselective alkylation of benzaldehyde with Et2Zn has been studied. This reaction is catalyzed by helical titanium complexes of tetradentate ligands and has been found to give good to excellent enantioselectivities.

Enantioselective addition of Et2Zn to benzaldehyde catalyzed by N-(S)-α-methylbenzyl-β-aminoalcohols

The enantioselective alkylation of benzaldehyde by diethylzine in the presence of catalytic amounts of N-(S)-α-methylbenzyl-β-aminoalcohols as the dilithium salts was studied. The extent of asymmetric induction was found to depend strongly upon the structure of catalyst used and also on the presence of lithium chloride.

Chiral diethanolamines and their lithium alcoholates as catalysts in the enantioselective alkylation of benzaldehyde by diethylzinc.

The enantioselective alkylation of benzaldehyde by diethylzinc in the presence of catalytic amounts of bis- erythro diethanolamines and their lithium alcoholates was studied. The extent of asymmetric induction was found to depend strongly upon subtle changes in the structure of the catalyst used.