Asymmetric Michael addition reactions using a chiral La–Na aminodiolate catalyst
TL;DR: In this paper, a chiral ligand was used in the synthesis of an optically active lanthanum-sodium amino diol complex LS-1, and the adducts were obtained in high yield with moderate to high enantiomeric excess under extremely mild conditions.
Abstract: (R,R)-(+)-2-[Benzyl-(2-hydroxy-2-phenylethyl)amino]-1-phenylethanol 1 is used as a chiral ligand in the synthesis of an optically active lanthanum–sodium amino diol complex LS-1. This heterobimetallic catalyst is quite effective as an asymmetric catalyst for various Michael addition reactions, 1H NMR study indicates the co-ordination of enone to the central lanthanum atom in LS-1. The reaction conditions were optimized and the adducts were obtained in high yield with moderate to high enantiomeric excess under extremely mild conditions.
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TL;DR: In this article, an effective enantioselective synthetic method based on a new concept of double catalytic activation was developed, in which both electrophile and nucleophile precursors are activated by use of catalytic amounts of chiral Lewis acid and amine base, respectively.
64 citations
TL;DR: In this paper, a new category of β-amino alcohols with a bicyclo[3.3.0] octane scaffold has been synthesized and used in the direct asymmetric nitroaldol reaction (Henry reaction).
Abstract: A new category of β-amino alcohols with a bicyclo[3.3.0]octane scaffold has been synthesized and used in the direct asymmetric nitroaldol reaction (Henry reaction). Up to 74% ee was obtained with the addition of nitromethane to relatively bulky aldehydes.
62 citations
TL;DR: Four novel heterobimetallic complexes stabilized by chiral phenoxy-functionalized prolinolate, highly active in catalyzing the epoxidation of α,β-unsaturated ketones, while the enantioselectivity varies according to the ionic radii of the rare earth center.
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TL;DR: In this paper, the conjugate addition of thioacetic acid to methacrylamides with chiral C 2 -symmetric trans-2,5-disubstituted pyrrolidines afforded the addition products in excellent stereoselectivities (>99% de) and good yields (80-90%).
Abstract: The conjugate addition of thioacetic acid to methacrylamides with chiral C 2 -symmetric trans -2,5-disubstituted pyrrolidines afforded the addition products in excellent stereoselectivities (>99% de) and good yields (80–90%). The high selectivity was attributed mainly to the steric effect of the chiral auxiliaries. The cyclic nature of the chiral auxiliaries seemed also important for both the stereoselectivity and the reaction rate. Acidic hydrolysis of the adduct containing (2 R ,5 R )-bis(methoxymethyl)pyrrolidine gave ( S )-3-mercapto-2-methylpropanoic acid, a key intermediate for captopril, in 98% ee and 96% yield. The chiral auxiliary was recovered in the demethylated form of N -Boc-(2 R ,3 R )-bis(hydroxymethyl)pyrrolidine in 90% yield.
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TL;DR: In this paper, the authors describe the development of rare-earth-alkali metal complexes such as LnM3tris(binaphthoxide) complexes (LnMB, Ln = rare earth metal, M = alkali metal), which are readily prepared from corresponding rare earth trichlorides or rare earth isopropoxides, and their application to catalytic asymmetric synthesis.
Abstract: This review focuses on a new concept in catalytic asymmetric reactions that was first realized for the use of heterobimetallic complexes. As these heterobimetallic complexes function as both a Bronsted base and as a Lewis acid, just like an enzyme, they make possible a variety of efficient catalytic asymmetric reactions. This heterobimetallic concept should prove to be applicable to a variety of new asymmetric catalyses. The first part of this review describes the development of rare-earth–alkali metal complexes such as LnM3tris(binaphthoxide) complexes (LnMB, Ln = rare-earth metal, M = alkali metal), which are readily prepared from the corresponding rare-earth trichlorides or rare-earth isopropoxides, and their application to catalytic asymmetric synthesis. By using a catalytic amount of LnMB complexes several asymmetric reactions proceed efficiently to give the corresponding desired products in up to 98% ee: LnLB-catalyzed asymmetric nitroaldol reactions (L = Li), LnSB-catalyzed asymmetric Michael reactions (S Na), and LnPB-catalyzed asymmetric hydrophosphonylations of either imines or aldehydes (P K). Applications of these heterobimetallic catalysts to the syntheses of several biologically and medicinally important compounds are also described. Spectral analyses and computational simulations of the asymmetric reactions catalyzed by the heterobimetallic complexes reveal that the two different metals play different roles to enhance the reactivity of both reaction partners and to position them. From mechanistic considerations, a useful activation of the heterobimetallic catalyses was realized by addition of alkali metal reagents. The second part describes the development of another type of heterobimetallic catalysts featuring Group 13 elements such as Al and Ga as the central metal. Among them, the AlLibis(binaphthoxide) complex (ALB) is an effective catalyst for asymmetric Michael reactions, tandem Michael–aldol reactions, and hydrophosphonylation of aldehydes.
586 citations
TL;DR: A remarkable diversity is also seen in the structures of the active sites of these di- and trinuclear metalloenzymes, even for enzymes that catalyze very similar reactions, including hydrolytic cleavage of phosphomono-, -di- and -triester bonds, phosphoanhydride bonds as well as of peptide bonds or urea.
Abstract: Numerous studies, both in enzymatic and nonenzymatic catalysis, have been undertaken to understand the way by which metal ions, especially zinc ions, promote the hydrolysis of phosphate ester and amide bonds. Hydrolases containing one metal ion in the active site, termed mononuclear metallohydrolases, such as carboxypeptidase. A and thermolysin were among the first enzymes to have their structures unraveled by X-ray crystallography. In recent years an increasing number of metalloenzymes have been identified that use two or more adjacent metal ions in the catalysis of phosphoryl-transfer reactions (R-OPO3 + R′-OH R′-OPO3 + R-OH; in the case of the phosphatase reaction R′-OH is a water molecule) and carbonyl-transfer reactions, for example, in peptidases or other amidases. These dinuclear metalloenzymes catalyze a great variety of these reactions, including hydrolytic cleavage of phosphomono-, -di- and -triester bonds, phosphoanhydride bonds as well as of peptide bonds or urea. In addition, the formation of the phosphodiester bond of RNA and DNA by polymerases is catalyzed by a two-metal ion mechanism. A remarkable diversity is also seen in the structures of the active sites of these di- and trinuclear metalloenzymes, even for enzymes that catalyze very similar reactions. The determination of the structure of a substrate, product, stable intermediate, or a reaction coordinate analogue compound bound to an active or inactivated enzyme is a powerful approach to investigate mechanistic details of enzyme action. Such studies have been applied to several of the metalloenzymes reviewed in this article; together with many other biochemical studies they provide a growing body of information on how the two (or more) metal ions cooperate to achieve efficient catalysis.
553 citations
TL;DR: In this article, the authors reported several carbon-carbon bond-forming reactions catalyzed by rare earth metal alkoxides and their application to a catalytic asymmetric nitroaldol reaction.
Abstract: In a recent paper, the authors reported that Zr(O-t-Bu){sub 4} was an efficient and convenient basic reagent in organic synthesis. However, all reactions examined were performed with stoichiometric quantities of the reagent. The authors envisioned that rare earth metal alkoxides would be stronger bases than group 4 metal alkoxides due to the lower ionization potential (ca. 5.4-6.4 eV) and the lower electronegativity (1.1-1.3) of rare earth elements; thus, the catalytic use of rare earth metal alkoxides in organic synthesis was expected. Although a variety of rare earth metal alkoxides have been prepared for the last three decades, to the authors knowledge, there have been few reports concerning the basicity of rare earth metal alkoxides. Herein, the authors report several carbon-carbon bond-forming reactions catalyzed by rare earth metal alkoxides and their application to a catalytic asymmetric nitroaldol reaction.
500 citations
268 citations