Chiral Aluminum Complexes Research Articles

BINOL-Al catalysed asymmetric cyclization and amplification: preparation of optically active menthol analogs.

We report a highly selective asymmetric ring-closing ene reaction catalysed by aluminum complexes with chiral BINOL. This reaction yields optically active 6-membered cyclized alcohols from unsaturated aldehydes, with good diastereo- and enantioselectivities. Asymmetric amplification of this reaction was investigated by varying the ee of the BINOL employed in the catalyst.

Kinetic resolution of citronellal by chiral aluminum catalysts: l-menthol synthesis from citral

We developed a highly reactive catalytic ring-closing ene reaction with chiral aluminum complexes. Kinetic resolutions of citronellal successfully afforded 68% ee of diastereoselective isopulegol and 62% ee of citronellal at 47% conversion with the BINOL-Al catalyst. l-Menthol was synthesized from citral with kinetic resolutions.

Dual Catalyst System for Asymmetric Alternating Copolymerization of Carbon Dioxide and Cyclohexene Oxide with Chiral Aluminum Complexes: Lewis Base as Catalyst Activator and Lewis Acid as Monomer Activator

Optically active aluminum complexes such as Schiff base, binuclear β-ketoiminate, and bisprolinol complexes were found to promote asymmetric alternating copolymerizations of carbon dioxide and cyclohexene oxide. The aluminum Schiff base complexes–tetraethylammonium acetate afforded isotactic poly(cyclohexene carbonate)s with low enantioselectivities. Lewis bases having two coordinating sites were utilized to enhance activity and selectivity based on the binuclear structure of the aluminum β-ketoiminate clarified by X-ray crystallography. [2gAlMe]2–bulky bisimidazole produced the alternating copolymer with high enantioselectivity (62% ee). The polymerization is considered to preferentially proceed at more crowded, enantioselective site owing to coordination of bulky Lewis bases to aluminums in less enantioselective sites. 32AlMe–2-picoline also exhibited a high enantioselectivity (67% ee). Methylaluminum bis(2,6-di-tert-butyl-4-methylphenoxide) was applied to perform faster and more enantioselective copolymerizations at low temperature (82% ee). The asymmetric copolymerizations were found to be significantly dependent on size of epoxide, temperature, and kind/amount of activators.

Aluminum Oxidation Catalysis under Aqueous Conditions: Highly Enantioselective Sulfur Oxidation Catalyzed by Al(salalen) Complexes

Asymmetric oxidation catalysis with an aluminum-based complex was achieved by a combination of newly synthesized chiral aluminum(salalen) complexes (salalen = half-reduced salen = salan/salen-hybridized [ONNO]-type tetradentate ligand; salan = reduced salen, salen = N,N'-ethylenebis(salicylideneiminato)) derived from binol (1,1'-bi-2,2'-naphthol) with aqueous hydrogen peroxide as the oxidant. The combination was found to be efficient for asymmetric sulfur oxidation. Various sulfides were smoothly converted into the corresponding sulfoxides with high to excellent enantioselectivity. Thioacetals are also good substrates for the oxidation.

ChemInform Abstract: Chiral Aluminum Complexes as Catalysts in Asymmetric Baeyer—Villiger Reactions of Cyclobutanones.

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.

Chiral aluminum complexes as catalysts in asymmetric Baeyer-Villiger reactions of cyclobutanones

BINOL-aluminum complexes were successfully employed as mediators and catalysts in asymmetric Baeyer-Villiger rearrangements of cyclobutanones. Good enantioselectivies were achieved with only 15 mol% of the chosen chiral Lewis acid. The enantiomeric excesses obtained have never been reached before in such metal-catalyzed Baeyer-Villiger reactions.Key words: aluminum, asymmetric catalysis, lactones, oxidations, rearrangement.

Chiral Salen–Aluminum Complexes as Catalysts for Enantioselective Aldol Reactions of Aldehydes and 5-Alkoxyoxazoles: An Efficient Approach to the Asymmetric Synthesis of syn and anti -Hydroxy--amino Acid Derivatives

Chiral aluminum complexes 3 have been employed as catalysts for the stereoselective synthesis of cis-5-substituted 2-oxazoline-4-carboxylates from the aldol reaction of oxazole 1 and aldehydes. cis-Product diastereoselection ranges from 3:1–50:1, while enantioselectivities vary from 92–99 % for reactions with the 25 aromatic aldehydes investigated. Supporting information for this article is available on the WWW under http://www.angewandte.com or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Chiral Salen-Aluminum Complexes as Catalysts for Enantioselective Aldol Reactions of Aldehydes and 5-Alkoxyoxazoles: An Efficient Approach to the Asymmetric Synthesis ofsyn andantiβ-Hydroxy-α-amino Acid Derivatives

Chiral aluminum complexes 3 have been employed as catalysts for the stereoselective synthesis of cis-5-substituted 2-oxazoline-4-carboxylates from the aldol reaction of oxazole 1 and aldehydes. cis-Product diastereoselection ranges from 3:1–50:1, while enantioselectivities vary from 92–99 % for reactions with the 25 aromatic aldehydes investigated.

On the mechanism of catalytic enantioselective hetero-Diels–Alder reactions of carbonyl compounds catalyzed by chiral aluminum complexes—a concerted, step-wise or Mukaiyama–aldol pathway

The mechanism for the hetero-Diels–Alder reaction of benzaldehyde with Danishefsky's diene catalyzed by various types of achiral and chiral aluminum complexes has been studied from a theoretical point of view using semi-empirical and ab initio calculations. The uncatalyzed reaction proceeds as a concerted reaction with an unsymmetrical transition state. The catalytic reaction has been studied using first (MeO) 2AlMe, followed by ( S)-BINOL-AlMe as the catalysts, and the transition states and intermediates have been calculated for different reaction paths. The catalyst activates benzaldehyde making the carbon atom in the carbonyl functionality more electrophilic. Attempts to calculate a concerted reaction path failed. However, a two-step process, the first step being a nucleophilic attack of the activated diene to the carbonyl carbon atom, with a transition-state energy of up to 13 kcal mol −1, depending on the catalyst and calculation method used, was found to take place leading to an aldol-like local energy-minimum intermediate. The second step, the ring-closure, which has a significantly lower transition-state energy leads to the hetero-Diels–Alder adduct. The mechanistic aspects of the catalytic hetero-Diels–Alder reaction is discussed on the basis of the calculations.

Chiral aluminum complexes as catalysts in asymmetric Baeyer-Villiger reactions of cyclobutanones

Chiral aluminum complexes as catalysts in asymmetric Baeyer-Villiger reactions of cyclobutanones

Development of an Unusually Highly Enantioselective Hetero-Diels-Alder Reaction of Benzaldehyde with Activated Dienes Catalyzed by Hypercoordinating Chiral Aluminum Complexes

Development of an Unusually Highly Enantioselective Hetero-Diels-Alder Reaction of Benzaldehyde with Activated Dienes Catalyzed by Hypercoordinating Chiral Aluminum Complexes

Development of an unusually highly enantioselective hetero-Diels-Alder reaction of benzaldehyde with activated dienes catalyzed by hypercoordinating chiral aluminum complexes

The effect of Lewis acid catalysis of the hetero-Diels-Alder reaction between benzaldehyde and activated dienes (e.g. the Danishefsky's diene) has been investigated. In the present work we decided to study a series of chiral aluminum complexes as potential catalysts for the hetero-Diels-Alder reaction in order to gain a better understanding of the effect on the chiral induction of varying the steric and electronic environment of the metal ion. The results of this study prompted us to conclude that steric effects in the ligand coordination sphere and hypercoordination are strongly contributing factors to the optical yield of the reaction. Optimization of the reaction culminated in the synthesis of the hetero-Diels-Alder product in 99.4% ee and 97% yield of the isolated product. Based on the experimental results the mechanism for the hetero-Diels-Alder reaction is discussed and it is postulated that hypercoordination to the chiral aluminum Lewis acid center is of importance for the reaction.

ChemInform Abstract: Chiral Aluminum Complexes as Phospho‐Transfer Catalysts.

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: A Highly Chemo‐ and Enantioselective Hetero‐Diels‐Alder Reaction Catalyzed by Chiral Aluminum Complexes.

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.