Showing papers on "Chiral Lewis acid published in 2009"
TL;DR: complex [4j](2)Al(III)Cl isolated as a white solid displayed similar reactivity as that prepared in situ, and reaction between alpha-isocyanoacetamides and aldehydes afforded the corresponding 5-aminooxazoles in good yields and enantioselectivities.
Abstract: A chiral Lewis acid catalyst was prepared by mixing 2 equiv of chiral binol-derived organophosphoric acid and 1 equiv of Et2AlCl. In the presence of a catalytic amount of [4j]2Al(III)Cl complex (0.05 equiv), reaction between α-isocyanoacetamides (2) and aldehydes (3) afforded the corresponding 5-aminooxazoles (1) in good yields and enantioselectivities. Complex [4j]2Al(III)Cl isolated as a white solid displayed similar reactivity as that prepared in situ.
98 citations
TL;DR: The diastereoselectivities presented are disparate to those previously reported for hetero-Diels-Alder reactions catalyzed by a chiral Lewis acid.
Abstract: A highly enantioselective anti-diastereoselective hetero-Diels−Alder reaction between a glyoxylate and siloxy- or methoxydienes using a chiral phosphoric acid catalyst that possesses less bulky phenyl groups at the 3 and 3′ positions of binaphthyl has been developed. The diastereoselectivities presented are disparate to those previously reported for hetero-Diels−Alder reactions catalyzed by a chiral Lewis acid.
86 citations
TL;DR: In this paper, Cinchona-derived chiral 2-aminobenzimidazole catalysts were obtained by the coupling of 5,7-bis(trifluoromethyl)-2-chlorobenzinamide with C( 9S)-aminodihydroquinine or C(9R)-aminodehydroquinidine and successively applied to the addition of dimethyl malonate to nitroolefins as very efficient chiral Lewis acid bifunctional organocatalysts.
Abstract: Efficient Cinchona-derived chiral 2-aminobenzimidazole catalysts were prepared by the coupling of 5,7-bis(trifluoromethyl)-2-chlorobenzimidazole with C(9S)-aminodihydroquinine or C(9R)-aminodihydroquinidine and successively applied to the Michael addition of dimethyl malonate to nitroolefins as very efficient chiral Lewis acid bifunctional organocatalysts (up to >99% ee).
49 citations
TL;DR: This work shows that nitrile ylide cycloadditions to electron-poor acceptors attached to chiral auxiliaries proceed in high yield and stereoselectivity in the absence of Lewis acids.
27 citations
TL;DR: A titanium-based chiral Lewis acid was found to be effective for the ring-opening reactions of meso-aziridines with aniline nucleophiles as mentioned in this paper.
Abstract: A titanium-based chiral Lewis acid was found to be effective for the ring-opening reactions of meso-aziridines with aniline nucleophiles. The products were generally isolated in high yields and with high to excellent enantioselectivity. The catalytic system was studied by X-ray single crystal analysis. In experiments on non-linear effects a strong non-linear effect of the catalyst system was observed.
26 citations
TL;DR: In this paper, the potential of native a-amino acids as chiral ligands in aqueous asymmetric Lewis acid catalysis, employing the C-C bond forming Michael addition as a model reaction, was explored.
25 citations
TL;DR: In this article, the chiral indole-based ligand families and their chromium(III) complexes were used as enantioselective catalysts for the conversion of propylene oxide and carbon monoxide to enantioenriched β-butyrolactone.
22 citations
TL;DR: A rare example of the application of a catalytic, enantioselective Diels-Alder cycloaddition to affect a kinetic resolution has been developed.
21 citations
TL;DR: In this paper, the authors highlight the enantioselective radical cyclization reactions catalyzed by chiral Lewis acid as well as organocatalyst and summarize the results.
Abstract: This review highlights the enantioselective radical cyclization reactions catalyzed by chiral Lewis acid as well as organocatalyst. The results of the radical cyclization controlled by chiral Al, Ti, Mg, Yb and Zn reagents, the oxidative cyclization using chiral amine, the chiral complexing agent-catalyzed reductive cyclization, transfer of chirality in radical cyclization, and so on are summarized.
20 citations
TL;DR: In this paper, a chiral Lewis acid mediated cyclization of the azetidin-2-one ring has been shown to yield up to 50% optical and chemical yields for β-lactam antibiotics.
14 citations
01 Jan 2009
TL;DR: In this article, the chiral bisoxazoline, 2,6-bis(oxazolinyl)pyridine, and related oxazoline ligands are shown to be quite effective in obtaining high levels of asymmtric induction.
Abstract: Highly enantioselective 1,3-dipolar cycloaddition reactions of several 1,3-dipoles, such as nitrones, nitrile oxides, nitrile imines, diazoalkanes, azomethine imines and carbonyl ylides, catalyzed by heterocyclic supramolecular type of metal complexes consisting of chiral heterocyclic compounds and metal salts were described in terms of their ability of asymmetric induction and enantioface differentiation. The scope and limitations of each cycloaddition reactions were also briefly described. Of the chiral hererocycle-based ligands, chiral bisoxazoline, 2,6-bis(oxazolinyl)pyridine, and related oxazoline ligands are shown to be quite effective in obtaining high levels of asymmtric induction. The combination of the bisoxazoline ligand derived from (1S,2R)-cis-1-amino-2-indanol and metal salts was especially efficient for asymmetric cycloaddition reactions of a number of 1,3-dipoles, such as nitrones, nitrile oxide, nitrile imines, diazoacetates and azomethine imines. The metals utilized for the heterocycle-based complexes show a crucial role for degree of asymmetric induction depending upon the 1,3-dipole used. High levels of enantioselectivity were achieved in 1,3-dipolar cycloaddition reactions of unstable carbonyl ylides with benzyloxyacetaldehyde derivatives, α-keto esters, 3-(2-alkenoyl)-2-oxazolidinones, and even vinyl ethers, which were catalyzed by Pybox-lanthanoid metal complexes.
TL;DR: In this paper, a chiral Lewis acid catalyzed enantioselective Nazarov reaction affording α-alkoxy cyclopentenones has been developed, which involves a nucleophilic attack of an alcohol on the α-position of the keto function.
Abstract: A chiral Lewis acid catalyzed enantioselective Nazarov reaction affording α-alkoxy cyclopentenones has been developed. This is the first example for construction of an asymmetric quaternary center by using the monodentate coordinated divinyl ketones via the interrupted Nazarov reaction, which involves a nucleophilic attack of an alcohol on the α-position of the keto function.
TL;DR: Chiral cationic palladium-BINAP catalyst in ionic liquid showed an excellent asymmetric catalytic activity in the Diels-Alder reactions using several dienes and the catalyst was easily recycled 7 times with good chemical yield and excellent enantioselectivity.
Abstract: Chiral cationic palladium-BINAP catalyst in ionic liquid showed an excellent asymmetric catalytic activity in the Diels-Alder reactions using several dienes and the catalyst was easily recycled 7 times with good chemical yield and excellent enantioselectivity (50-60%, 94-98% ee).
TL;DR: A titanium-based chiral Lewis acid was found to be effective for the ring-opening reactions of meso-aziridines with aniline nucleophiles.
Abstract: A titanium-based chiral Lewis acid was found to be effective for the ring-opening reactions of meso-aziridines with aniline nucleophiles. The products were generally isolated in high yields and with high to excellent enantioselectivity. The catalytic system was studied by X-ray single crystal analysis. In experiments on non-linear effects a strong non-linear effect of the catalyst system was observed.
TL;DR: In this article, four amino acids (alanine, valine, phenylalanine and phenylglycine) were converted into C 1-symmetrical salen ligands and complexed to titanium, vanadium, copper and cobalt.
Abstract: Four amino acids (alanine, valine, phenylalanine and phenylglycine) have been converted into C1-symmetrical salen ligands and complexed to titanium, vanadium, copper and cobalt. The resulting complexes have been used as asymmetric catalysts for asymmetric cyanohydrin synthesis, asymmetric Strecker reactions, asymmetric synthesis of α-methyl amino acids and asymmetric Darzens condensations. Satisfactory levels of asymmetric induction were obtained from reactions in which the (salen)metal complex acts as a chiral Lewis acid, but low levels of asymmetric induction were obtained from reactions carried out under solid–liquid phase-transfer conditions.
TL;DR: In this article, the authors highlight the enantioselective radical cyclization reactions catalyzed by chiral Lewis acid as well as organocatalyst and summarize the results.
Abstract: This review highlights the enantioselective radical cyclization reactions catalyzed by chiral Lewis acid as well as organocatalyst. The results of the radical cyclization controlled by chiral Al, Ti, Mg, Yb and Zn reagents, the oxidative cyclization using chiral amine, the chiral complexing agent-catalyzed reductive cyclization, transfer of chirality in radical cyclization, and so on are summarized.