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Mayer, Sandra F.; Kroutil, Wolfgang; Faber, Kurt

doi:10.1039/b105493g

Cited by 194 publications

(76 citation statements)

References 23 publications

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“…[28][29][30][31] A major problem encountered in the design of catalytic cascade processes is the incompatibility of the different catalysts and a possible solution is compartmentalization (i.e., immobilization) of the different catalysts thus circumventing their mutual interaction which could result in inhibition and or deactivation.…”

Section: Introductionmentioning

confidence: 99%

Enzyme Immobilization: The Quest for Optimum Performance

2007

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Immobilization is often the key to optimizing the operational performance of an enzyme in industrial processes, particularly for use in non-aqueous media. Different methods for the immobilization of enzymes are critically reviewed. The methods are divided into three main categories, viz. (i) binding to a prefabricated support (carrier), (ii) entrapment in organic or inorganic polymer matrices, and (iii) cross-linking of enzyme molecules. Emphasis is placed on relatively recent developments, such as the use of novel supports, e.g., mesoporous silicas, hydrogels, and smart polymers, novel entrapment methods and cross-linked enzyme aggregates (CLEAs).

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Section: Introductionmentioning

confidence: 99%

Enzyme Immobilization: The Quest for Optimum Performance

2007

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“…Cascade (or domino) reactions are common in natural (enzyme-catalyzed) systems (40) and are of increasing importance in organic synthesis (41). To the best of our knowledge, the reaction of Scheme 4 represents the first example of a cascade reaction in which (molecular) chemistry that was performed on a ligand triggered (supramolecular) ligand exchange.…”

Section: Resultsmentioning

confidence: 99%

“…It was demonstrated that selective exchange of both ligands and ligand subcomponents occurs, permitting the dynamic reassembly of these complexes on both supramolecular and molecular levels. A previously undocumented kind of cascade reaction (40,41) was also introduced, whereby the addition of one ligand-component molecule cleanly induces two distinct rearrangements to occur.…”

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confidence: 99%

Dynamic covalent and supramolecular direction of the synthesis and reassembly of copper(I) complexes

Schultz

Nitschke

2005

Proc. Natl. Acad. Sci. U.S.A.

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The technique of subcomponent self-assembly has been applied to the preparation of a set of copper(I) complexes from diamines and aldehydes in aqueous solution. These complexes may be synthesized alongside one another in solution despite the chemical nonorthogonality of their respective starting materials; thermodynamic equilibration eliminates all mixed products. The reactivity of these complexes has been studied, revealing that in certain cases, the substitution of both ligands and ligand subcomponents could be independently carried out. In one particular case, a complex was shown to be inert to ligand substitution but readily underwent ligand subcomponent substitution, creating the possibility of a previously undocumented kind of cascade reaction: Once ligand subcomponent substitution had occurred, ligand exchange could then happen, allowing both reactions to be triggered by a single chemical event.self-assembly ͉ coordination chemistry ͉ cascade reactions T he generation of complex metal-containing architectures from simple building blocks through self-assembly (1-8) is a compelling means by which to build up functional molecular machines (9-11). Such molecular devices are beginning to give substance to the promises of nanotechnology; recent examples include Mirkin and coworkers' (12) signal-amplifying allosteric catalyst, Nolte and colleagues' (13) ''chain-walking'' epoxidation catalyst, Leigh and coworkers' (14) reversible molecular motor, and the molecular elevator of Stoddart and colleagues (15).A powerful technique in metallo-organic self-assembly consists of the simultaneous formation of covalent (carbonheteroatom) and dative (heteroatom-metal) bonds, bringing both ligand and complex into being at the same time. This ''subcomponent self-assembly'' has its roots in the template synthesis of Busch and coworkers (16) and has recently been used in the synthesis of a wealth of structures, including rotaxanes (17), catenanes (18), helicates (19-22), grids (23-25), and a Borromean link (26). These structures belong to the domains of both dynamic covalent (27) and supramolecular (28) Because subcomponent self-assembly reactions operate on two distinct levels simultaneously, one might expect that these reactions would give rise to mixtures of diverse products or large dynamic combinatorial libraries (30-35), as the multiple components combine in different ways. Although many structures might in theory be possible at both covalent and supramolecular levels, the metal and the subcomponents of the ligand may be chosen such that the thermodynamic preferences of both converge to give rise to a single product or a limited number of products (22)(23)(24)(36)(37)(38). It is important to note that it is the reversible formation of intraligand imine bonds (in addition to the metal-ligand bonds) that allows for this dynamic sorting͞ selection effect to occur.Along similar lines, although the addition of further ligand components might be expected to increase the number of species present in the product mixture, it is non...

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“…[1] However, those involving more than one mutually compatible catalyst are much less common. [2] Furthermore, the use of site-isolated catalysts that would otherwise be mutually destructive and thus ineffective in solution phase to facilitate reaction cascades is in its infancy. [3] Although pioneered around 30 years ago by Cohen et al, [4] recent papers reporting new ways of preventing mutual deactivation of reagents have brought site isolation to the forefront again.…”

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confidence: 99%

Site‐Isolated Base‐ and Acid‐Mediated Michael‐Initiated Cyclization Cascades

2007

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Cascade reactions are attractive in modern synthetic strategies as they enable several bond-forming events to occur in the same reaction vessel without the necessary drain of resources associated with one-reaction, one-pot approaches. [1] This allows rapid and efficient syntheses of complex molecules from relatively simple starting materials whilst minimizing cost and waste, and thus, the impact of the chemistry on the environment. Many examples involving cascade sequences catalyzed by a single chemical entity have been reported.[1] However, those involving more than one mutually compatible catalyst are much less common.[2] Furthermore, the use of site-isolated catalysts that would otherwise be mutually destructive and thus ineffective in solution phase to facilitate reaction cascades is in its infancy. [3] Although pioneered around 30 years ago by Cohen et al., [4] recent papers reporting new ways of preventing mutual deactivation of reagents have brought site isolation to the forefront again. [5,6] Reported sequences have included acid-and base-catalyzed condensation of carbonyl compounds with active methylene compounds to form electrondeficient alkenes, which are subsequently attacked by a nucleophilic reagent or reduced by using hydrogen over a palladium catalyst. However, to date the concept has not been exploited to generate complex molecular structures and accordingly, we believed the true synthetic power of cascades catalyzed by both basic and acidic reagents in one pot was still to be realized.By combining a base-catalyzed intermolecular Michael addition reaction of an a,b-unsaturated carbonyl compound 1 and a suitable amide pronucleophile 2 with an acid-catalyzed intramolecular N-acyl iminium ion cyclization [7] of the resulting adduct 3, we believed site isolated base and acid (SIBA) catalysis could be exploited to form structurally complex multiring heterocyclic molecules 4 in one pot and under mild conditions (Scheme 1). With five points of diversity present in the reaction products, this procedure could be a powerful tool for both library generation and target synthesis. Herein we present our findings.Proof-of-principle studies were required to determine the necessity and feasibility of the SIBA catalysis cascade. b-Keto amide 5 containing an acidic methine group and pendant nucleophilic pyrrole substituent was chosen as a test substrate. When a dichloromethane solution of 5 and methyl vinyl ketone 6 (1.1 equiv) at room temperature was treated with PS-BEMP [8] (10 %), Michael adduct 7 was formed as the sole reaction product in an excellent yield.[9] When the reaction was repeated by using Amberlyst A15 (200 %) in the presence or absence of liquid BEMP (10 %), the only observed reaction product was substituted pyrrole 8 in 68 % yield; 7 was not present in the reaction mixture. However, when the reaction was repeated by using a combination of PS-BEMP (10 %) and Amberlyst A15 (200 %), the sole reaction product was the desired tetracyclic product 9 produced in 83 % yield as a 1:1 mixture of diastereoiso...

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Untitled

Cited by 194 publications

References 23 publications

Enzyme Immobilization: The Quest for Optimum Performance

Enzyme Immobilization: The Quest for Optimum Performance

Dynamic covalent and supramolecular direction of the synthesis and reassembly of copper(I) complexes

Site‐Isolated Base‐ and Acid‐Mediated Michael‐Initiated Cyclization Cascades

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