Lewis Acid Catalysis In Water Research Articles

A synergistic LUMO lowering strategy using Lewis acid catalysis in water to enable photoredox catalytic, functionalizing C-C cross-coupling of styrenes.

Easily available α-carbonyl acetates serve as convenient alkyl radical source for an efficient, photocatalytic cross-coupling with a great variety of styrenes. Activation of electronically different α-acetylated acetophenone derivatives could be effected via LUMO lowering catalysis using a superior, synergistic combination of water and (water-compatible) Lewis acids. Deliberate application of fac-Ir(ppy)3 as photocatalyst to enforce an oxidative quenching cycle is crucial to the success of this (umpolung type) transformation. Mechanistic particulars of this dual catalytic coupling reaction have been studied in detail using both Stern-Volmer and cyclic voltammetry experiments. As demonstrated in more than 30 examples, our water-assisted LA/photoredox catalytic activation strategy allows for excess-free, equimolar radical cross-coupling and subsequent formal Markovnikov hydroxylation to versatile 1,4-difunctionalized products in good to excellent yields.

Entropy-Controlled and Enantiodivergent Lewis Acid Catalysis in Water

Developing new and useful methods in asymmetric catalysis is of continuous importance. A current challenge is to address the imperatives of green chemistry, such that processes maximize resource-efficiency and minimize the generation of waste. To this end, this article discloses the potential of alpha-amino acids in the development of entropy-controlled and enantiodivergent Lewis acid catalysis. In an ytterbium-catalyzed aqueous Michael addition reaction, natural alpha-amino acids induced not only a large rate acceleration, but also an unusual and remarkable reversed temperature effect on enantioselectivity. As demonstrated with 17 alpha-amino acids, the enantioselectivity of the reaction can be significantly altered, and even reversed, simply by modifying the reaction temperature. After determining differential thermodynamic activation parameters, it was revealed that an unusually large entropy contribution was responsible for the observed effects. By further correlation to the influence of the aqueous medium, we put forward the concept of stereospecific aqueous solvation (SAS), which describes the bearing of aqueous solvation on the equilibrium of diastereomeric transition states, and thus on the R/S ratio of the product. (Less)

ChemInform Abstract: Green Acid Catalysis in Water

AbstractReview: 113 refs.

Chiral Lewis Acid Catalysis in Water

Chiral Lewis Acid Catalysis in Water

Asymmetric Lewis Acid Catalysis in Water: α‐Amino Acids as Effective Ligands in Aqueous Biphasic Catalytic Michael Additions

AbstractThis article explores the potential of native α‐amino acids as chiral ligands in aqueous asymmetric Lewis acid catalysis, employing the C–C bond forming Michael addition as a model reaction. Some insights are provided regarding the details of Yb(OTf)3/α‐amino acid‐catalyzed Michael additions in water through new kinetic data as well as studies on how both yield and selectivity are influenced by variations in metal/ligand ratio, pH, temperature, and structure of the α‐amino acid. Through this investigation it was found that reaction conditions that require only 5 mol‐% of the Lewis acid, provides enantiomeric excesses of up to 79 % and is applicable to a wider range of donors and acceptors than previously demonstrated. Importantly, it was also demonstrated that the α‐amino acid complexed ytterbium catalyst might have potential for large‐scale applications as it displays not only large ligand accelerations, but also good solubility and stability in water. It can be recycled multiple times without appreciable loss of activity. The result is a promising example of a water‐compatible chiral Lewis acid.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

ChemInform Abstract: Lewis Acid Catalysis in Water with a Hydrophilic Substrate: Scandium‐Catalyzed Hydroxymethylation with Aqueous Formaldehyde in Water.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 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.

Lewis Acid Catalysis in Water with a Hydrophilic Substrate: Scandium‐Catalyzed Hydroxymethylation with Aqueous Formaldehyde in Water

Lewis Acid Catalysis in Water with a Hydrophilic Substrate: Scandium‐Catalyzed Hydroxymethylation with Aqueous Formaldehyde in Water

Lewis Acid Catalysis in Water with a Hydrophilic Substrate: Scandium-Catalyzed Hydroxymethylation with Aqueous Formaldehyde in Water

Nasse Sache: Bei der hoch selektiven Titelreaktion sind Säure-Base-Wechselwirkungen zwischen dem Sc-Katalysator und HCHO wichtig. Die Synthese eines Duftstoffs belegt die Nützlichkeit der Reaktion (siehe Schema, der Ligand DS ist nicht gezeigt; PI-Pd=in Polymer eingeschlossenes Palladium, BTF=Benzotrifluorid).

Expanding the Scope of Lewis Acid Catalysis in Water: Remarkable Ligand Acceleration of Aqueous Ytterbium Triflate Catalyzed Michael Addition Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Expanding the Scope of Lewis Acid Catalysis in Water: Remarkable Ligand Acceleration of Aqueous Ytterbium Triflate Catalyzed Michael Addition Reactions

[reaction: see text] Significant rate acceleration of metal-catalyzed Michael addition reactions in water was observed upon addition of small, dibasic ligands. Ytterbium triflate and TMEDA was the most effective combination leading to a nearly 20-fold faster reaction than in the absence of ligand.

A Nanostructured, Scandium-Containing Polymer for Heterogeneous Lewis Acid Catalysis in Water

A nanostructured, polymer-supported Sc(III) catalyst for heterogeneous Lewis acid catalysis in water was prepared by quantitative Sc(III) exchange of a cross-linked inverted hexagonal assembly containing sodium sulfonate groups. The material was found to catalyze Mukaiyama aldol and Mannich reactions with a syn/anti product ratio of ca. 2/1, whereas Sc(III) catalysts in solution and on amorphous polymer supports do not show any significant syn/anti diastereoselectivity under similar conditions.

Effects of Lewis acid-surfactant-combined catalysts on aldol and Diels-Alder reactions in water

Aldol and Diels-Alder reactions in water in the presence of various dodecyl sulfate and dodecanesulfonate salts as Lewis acid-surfactant-combined catalysts have been studied. In the aldol reactions, these salts differed from each other with respect to their catalytic ability at the initial stage of the reaction and to the final yields of the aldol product, while these salts did not affect the reaction rates of the Diels-Alder reactions. These results disclose the remarkable characteristics of Lewis acid catalysis in water.