A dendrimer-supported heterobimetallic asymmetric catalyst

Arai, Takayoshi; Sekiguti, Tetuya; Iizuka, Yoshimasa; Takizawa, Shinobu; Sakamoto, Shigeru; Yamaguchi, Kentaro; Sasai, Hiroaki

doi:10.1016/s0957-4166(02)00573-6

Cited by 40 publications

(16 citation statements)

References 30 publications

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“…10.2.1 Dendrimer-supported MACs [4] Dendrimers are a class of spherical polymers with hyperbranched chains, possessing a central core with a specific number of dendron units attached. The structure, size, FIGURE 10.2.…”

Section: Dendrimer-supported and Dendronized Polymer-supported Macsmentioning

confidence: 99%

Immobilization of Multicomponent Asymmetric Catalysts (MACs)

Sasai

Takizawa

2011

Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis

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Section: Dendrimer-supported and Dendronized Polymer-supported Macsmentioning

confidence: 99%

Immobilization of Multicomponent Asymmetric Catalysts (MACs)

Sasai

Takizawa

2011

Polymeric Chiral Catalyst Design and Chiral Polymer Synthesis

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“…The catalytic asymmetric reaction gave the corresponding ketone 26 in 94% ee, this being a key building block in the synthesis of coronafic acid 27. Furthermore, Sasai and coworkers have shown that heterobimetallic BINOL-derived dendrimer complexes exhibit excellent enantioselectivity for the catalytic ECAs shown in Eqs 4.11 and 4.12 [25]. These dendrimer complexes may also be employed as efficient supports, with the catalyst capable of being recycled at least three times.…”

Section: Heterobimetallic Rare-earth-alkali Metal-binol Complexes In mentioning

confidence: 99%

Asymmetric Bifunctional Catalysis Using Heterobimetallic and Multimetallic Systems in Enantioselective Conjugate Additions

Córdova

2010

Catalytic Asymmetric Conjugate Reactions

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The conjugate addition of a nucleophile to an α,β-unsaturated carbonyl compound (commonly referred to as Michael addition) is a classic carbon-carbon bond-forming reaction in organic synthesis [1]. It is also an important transformation for the formation of carbon-heteroatom bonds. As these reactions often result in the creation of a stereogenic center, the importance of controlling the stereoselectivity of such conjugate addition reactions has sparked intense and impressive developments by chemists in both academia and industry. The use of stoichiometric amounts of chiral reagents, ligands, and auxiliaries has led to the development of several asymmetric Michael reactions [2]. However, the need to develop more effective and atom-economic methods has led to the utilization of asymmetric catalysis in enantioselective conjugate additions (ECAs) [3]. In Nature, natural catalysts -enzymes -mainly use general base and acid catalysis to achieve carbon-carbon bond-forming reactions, with almost exclusive stereocontrol [4]. This is accomplished in the active site of the enzyme by the perfect arrangement and dual activation of the electrophilic acceptor and nucleophilic donor substrate. Sometimes, a metallic cofactor in cooperation with the neighboring amino acids of the active site is necessary to achieve C−C bond-formation. In this context, type II aldolase enzymes employ a Zn ion (which is a Lewis acid) to activate dihydroxyacetone phosphate, in cooperation with an amino acid residue (which acts as a Brønsted base) to generate, regioselectively, an enolate (Figure 4.1a) [4]. At the same time, the electrophilic aldehyde acceptor is a Brønsted acid activated by an amino acid residue, such that stereoselective C−C bond-formation will occur with excellent enantioselectivity. In Nature, millions of years of evolution were required order to achieve this perfectly orchestrated transformation in an aqueous medium. Consequently, in taking their inspiration from Nature, research chemists have developed asymmetric catalysts that may reach impressive levels of enantioselectivity in carbon-carbon bond-forming reactions [5]. One way to achieve such enantioselectivity is to employ a strategy similar to that utilized by type II aldolase enzymes, which includes asymmetric bifunctional catalysis and metal activation (Figure 4.1b) Catalytic Asymmetric Conjugate Reactions. Edited by Armando Córdova

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“…Molecular dynamics simulation of the dendrimer-supported ALB catalysts with varying spacer lengths indicated that a C4 to C6 alkyl chain would be optimal [44]. Accordingly the synthesis of the dendrimer was initiated with 18 (see scheme 5) [45]. Two molecules of 18 were reacted with methyl 3,5-dihydroxybenzoate under the Mitsunobu conditions to obtain the terminal unit 37 in 66% yield, which was reduced with LiAlH 4 to afford the compound 38 in 98% yield.…”

Section: Dendrimer-supported Binol Ligandsmentioning

confidence: 99%

“…Two molecules of 18 were reacted with methyl 3,5-dihydroxybenzoate under the Mitsunobu conditions to obtain the terminal unit 37 in 66% yield, which was reduced with LiAlH 4 to afford the compound 38 in 98% yield. The resulting alcohol was subsequently coupled with 1,3,5-tris(4-hydroxyphenyl)benzene (39) [45] as the core to obtain the first-generation (G1) dendrimer 40, which contains six BINOL units at the terminal positions, in 63% yield. Deprotection of 40 using TBAF afforded the corresponding dendrimer-supported BINOL (G1 DSB) 41 in 92% yield.…”

Section: Dendrimer-supported Binol Ligandsmentioning

confidence: 99%

Development of efficient methods for the immobilisation of multicomponent asymmetric catalysts

Jayaprakash

Takizawa

Arai

et al. 2006

Journal of Experimental Nanoscience

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Immobilisation of multicomponent asymmetric catalysts has been achieved utilizing soluble polymers and dendrimers containing BINOL ligands. A novel approach based on the use of ''catalyst analogue'' helps to position the ligands suitably on the polymer backbone. Utilizing metal-bridged polymers, a simple and efficient method for immobilisation without the need for a polymer support has also been realized. Heterogeneous Al-Li-bis(binaphthoxide) and -oxodititanium complexes thus obtained have been used as catalysts for the asymmetric Michael addition and the asymmetric carbonyl-ene reactions respectively. The catalysts displayed high activity affording the corresponding products with high enantiomeric excesses. In many cases, the catalysts could be recovered and reused.

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A dendrimer-supported heterobimetallic asymmetric catalyst

Cited by 40 publications

References 30 publications

Immobilization of Multicomponent Asymmetric Catalysts (MACs)

Immobilization of Multicomponent Asymmetric Catalysts (MACs)

Asymmetric Bifunctional Catalysis Using Heterobimetallic and Multimetallic Systems in Enantioselective Conjugate Additions

Development of efficient methods for the immobilisation of multicomponent asymmetric catalysts

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