Lewis Acid-catalyzed Reactions Research Articles

Computational Catalysis Using the Artificial Force Induced Reaction Method.

The artificial force induced reaction (AFIR) method in the global reaction route mapping (GRRM) strategy is an automatic approach to explore all important reaction paths of complex reactions. Most traditional methods in computational catalysis require guess reaction paths. On the other hand, the AFIR approach locates local minima (LMs) and transition states (TSs) of reaction paths without a guess, and therefore finds unanticipated as well as anticipated reaction paths. The AFIR method has been applied for multicomponent organic reactions, such as the aldol reaction, Passerini reaction, Biginelli reaction, and phase-transfer catalysis. In the presence of several reactants, many equilibrium structures are possible, leading to a number of reaction pathways. The AFIR method in the GRRM strategy determines all of the important equilibrium structures and subsequent reaction paths systematically. As the AFIR search is fully automatic, exhaustive trial-and-error and guess-and-check processes by the user can be eliminated. At the same time, the AFIR search is systematic, and therefore a more accurate and comprehensive description of the reaction mechanism can be determined. The AFIR method has been used for the study of full catalytic cycles and reaction steps in transition metal catalysis, such as cobalt-catalyzed hydroformylation and iron-catalyzed carbon-carbon bond formation reactions in aqueous media. Some AFIR applications have targeted the selectivity-determining step of transition-metal-catalyzed asymmetric reactions, including stereoselective water-tolerant lanthanide Lewis acid-catalyzed Mukaiyama aldol reactions. In terms of establishing the selectivity of a reaction, systematic sampling of the transition states is critical. In this direction, AFIR is very useful for performing a systematic and automatic determination of TSs. In the presence of a comprehensive description of the transition states, the selectivity of the reaction can be calculated more accurately. For relatively large molecular systems, the computational cost of AFIR searches can be reduced by using the ONIOM(QM:QM) or ONIOM(QM:MM) methods. In common practice, density functional theory (DFT) with a relatively small basis set is used for the high-level calculation, while a semiempirical approach or a force field description is used for the low-level calculation. After approximate LMs and TSs are determined, standard computational methods (e.g., DFT with a large basis set) are used for the full molecular system to determine the true LMs and TSs and to rationalize the reaction mechanism and selectivity of the catalytic reaction. The examples in this Account evidence that the AFIR method is a powerful approach for accurate prediction of the reaction mechanisms and selectivities of complex catalytic reactions. Therefore, the AFIR approach in the GRRM strategy is very useful for computational catalysis.

ChemInform Abstract: Potential and Challenges of Zeolite Chemistry in the Catalytic Conversion of Biomass

AbstractReview: 421 refs.

Approach to Isoindolinones, Isoquinolinones, and THIQs via Lewis Acid-Catalyzed Domino Strecker-Lactamization/Alkylations.

A one-pot, three-component synthesis of widely substituted isoindolinones and isoquinolinones, featuring a Lewis acid-catalyzed efficient Strecker reaction and lactamization sequence, affording products in good to high yields is reported. The method has also been extended to the synthesis of tetrahydroisoquinolines (THIQs) in high yields.

Asymmetric Brønsted Base Catalyzed and Directed [3+2] Cycloaddition of 2-Acyl Cycloheptatrienes with Azomethine Ylides.

Conjugated cyclic trienes have the potential for different types of cycloaddition reactions. In the present work, we will, in a novel asymmetric cycloaddition reaction, demonstrate that the organocatalytic reaction of 2-acyl cycloheptatrienes with azomethine ylides proceeds as a [3+2] cycloaddition, which is in contrast to the Lewis acid-catalyzed reaction, in which a [3+6] cycloaddition takes place. In the presence of a chiral organosuperbase, 2-acyl cycloheptatrienes react in a highly enantioselective manner in the [3+2] cycloaddition with azomethine ylides, providing the 1,3-dipolar cycloaddition product in high yields and up to 99 % ee. It is also shown that the diene formed by the reaction can undergo stereoselective dihydroxylation, bromination, and cycloaddition reactions. Finally, based on experimental observations, some mechanistic considerations are discussed.

Potential and challenges of zeolite chemistry in the catalytic conversion of biomass.

Increasing demand for sustainable chemicals and fuels has pushed academia and industry to search for alternative feedstocks replacing crude oil in traditional refineries. As a result, an immense academic attention has focused on the valorisation of biomass (components) and derived intermediates to generate valuable platform chemicals and fuels. Zeolite catalysis plays a distinct role in many of these biomass conversion routes. This contribution emphasizes the progress and potential in zeolite catalysed biomass conversions and relates these to concepts established in existing petrochemical processes. The application of zeolites, equipped with a variety of active sites, in Brønsted acid, Lewis acid, or multifunctional catalysed reactions is discussed and generalised to provide a comprehensive overview. In addition, the feedstock shift from crude oil to biomass involves new challenges in developing fields, like mesoporosity and pore interconnectivity of zeolites and stability of zeolites in liquid phase. Finally, the future challenges and perspectives of zeolites in the processing of biomass conversion are discussed.

Expedient synthesis of tetrahydroquinoline-3-spirohydantoin derivatives via the Lewis acid-catalyzed tert-amino effect reaction.

Magnesium triflate was found to effectively catalyze the tert-amino effect reaction (T-reaction) involving ethyl 3-(2-(dialkylamino)-phenyl)-2-nitroacrylates leading to tetrahydroquinoline nitroester derivatives. These compounds can be readily transformed to the corresponding valuable spirohydantoin derivatives.

Lewis acid-catalyzed reactions of N-allylanilines with diazo compounds involving aza-Claisen rearrangement

N-Allyl-N-methylanilines react with methyl diazoacetate or diazoacetone in the presence of Y, Sc or Sm triflates to give the corresponding methyl N-(2-allylaryl)-N-methylglycinates or 2-allyl-N-methyl-N-(2-oxopropyl)aniline. The formation of these compounds involves the aza-Claisen rearrangement.

Lewis Acid-catalyzed Ring-opening Addition Reactions of Alcohols to Vinylcyclopropane

Abstract Lewis acids such as Sn(OTf)2, GaCl3, Sc(OTf)3, and Al(OTf)3 catalyzed ring-opening 1,5-addition reactions of aliphatic alcohols to dimethyl 2-vinylcyclopropane-1,1-dicarboxylate, resulting in moderate to high yields of methyl 4-alkoxy-2-methoxycarbonyl-5-hexenoates with a catalytic turnover number of up to 80. A deuterium-labeling experiment and comparison with the reactivity of dimethyl cyclopropane-1,1-dicarboxylate suggested that this reaction involves a 1,3-dipole intermediate stabilized by the donor and the acceptor substituents. The ring-opening addition of phenols demonstrated several reaction modes, including Friedel–Crafts 1,5- and 1,7-additions.

Enantioselective Lewis Acid Catalysis in Intramolecular [2 + 2] Photocycloaddition Reactions: A Mechanistic Comparison between Representative Coumarin and Enone Substrates.

The intramolecular [2 + 2] photocycloaddition of three 4-(alk-4-enyl)coumarins and three 1-(alk-4-enoyl)-2,3-dihydropyridones was studied in the absence and in the presence of Lewis acids (irradiation wavelength λ = 366 nm). Spectral and kinetic data were collected for the respective parent compounds with a pent-4-enyl and a pent-4-enoyl chain. For the substrates with a methyl group in cis- or trans-position of the terminal alkene carbon atom (hex-4-enyl and hex-4-enoyl substitution), the stereochemical outcome of the [2 + 2] photocycloaddition was investigated. The mechanistic course of the uncatalyzed coumarin reactions was found to be a singlet pathway, whereas Lewis acid-catalyzed reactions proceeded with higher reaction rates in the triplet manifold. Contrary to that, the dihydropyridones underwent a fast triplet reaction in the absence of the Lewis acid. In the presence of a chiral Lewis acid the reactions slowed down but, due to the high extinction coefficient of the Lewis acid/dihydropyridone complexes at λ = 366 nm, still resulted in high enantioselectivity.

Synthesis of α-Hydroxy Amides

α-Hydroxy amides are a class of important intermediates in organic synthesis. It plays an important role in the field of science and medicine. However, the preparation methods of α-hydroxy amides are relatively few, and they are usually enzyme-or Lewis acid-catalyzed reactions. These types of methods are not ideal in operation, yield and/or stereoselectivity. We found a new way to synthesize α-hydroxy amides by transforming amino acids into α-hydroxyl acids, and then by amination of the α-hydroxy acids.

Lewis acid-catalyzed reaction between tertiary enamides and imines of salicylaldehydes: expedient synthesis of novel 4-chromanamine derivatives

In the presence of a catalytic amount of Zn(OTf)2 in DCE at ambient temperature, a number of tertiary enamides underwent highly efficient reaction with imines of salicylaldehydes to afford diverse functionalized 4-chromanamine derivatives in high yields. The reaction proceeds most probably through an enaminic addition of tertiary enamides to imine functionality followed by the intramolecular interception of the resulting iminium intermediate by the phenolic hydroxy group. The synthesis was also practically implemented by means of a three-component reaction starting from salicylaldehyde, para-nitroaniline, and a tertiary enamide.

ChemInform Abstract: Three‐Component Povarov Reaction—Heteroannulation with Arynes: Synthesis of 5,6‐Dihydroindolo[1,2‐a]quinolines.

A reaction of 2-acyl substituted tetrahydroquinolines, prepared by Lewis acid-catalyzed three-component reaction of α-oxo aldehydes, anilines, and dienophiles, with in situ generated arynes afforded 5,6-dihydroindolo[1,2-a]quinolines in good to excellent yields.

A study in indol-2-yl carbinol chemistry and the application for the total synthesis of mersicarpine

We present an efficient protocol for the Lewis acid-catalyzed reaction of indol-2-yl carbinols with various π-nucleophiles including the heteroarenes such as indole, pyrrole, furan, as well as the silyl vinyl ethers. Most importantly, the precise use of this protocol enabled us to establish a very concise and practical route for the total synthesis of (±)-mersicarpine in eight linear steps with ca. 14% overall yield from commercially available indole and succinic anhydride. Moreover, the method developed herein would be broadly applicable for the diverse synthesis of a number of structurally intriguing indole alkaloids as well as biologically interesting hetero-triarylmethanes.

Challenges of and Insights into Acid-Catalyzed Transformations of Sugars

The selective transformation of hexose and pentose sugars to intermediate platform chemicals, such as furans, is an essential step in the conversion of cellulosic and hemicellulosic biomass to biofuels and biochemicals. Yet, many challenges in achieving commercially viable processes remain. In this feature article, we outline challenges that need to be overcome to enable these transformations. Then, we present the newly introduced acid-catalyzed isomerization of aldose sugars to ketose sugars via a class of solid Lewis acid catalysts (e.g., Sn-Beta, Ti-Beta). We elucidate mechanistic insights arising from subnanometer cooperativity and solvent effects that can be controlled to tune reaction pathways and selectivity and draw parallels between heterogeneous and homogeneous Lewis acid catalysts. Subsequently, we discuss fructose dehydration to 5-hydroxyl-methylfurfural (HMF) via homogeneous and heterogeneous Bronsted acid-catalyzed chemistry. We show how fundamental insights arising from the combination of kinetics, spectroscopy, and multiscale simulations rationalize the improved yield of HMF in water–organic cosolvents. The stability of heterogeneous Lewis acid catalysts under low pH enables tandem Bronsted and Lewis acid-catalyzed reactions in a single pot that overcomes equilibrium limitations and gives a high HMF yield starting from sugar raw materials. Additionally, we provide an overview of multicomponent adsorption of biomass derivatives from solution in microporous materials and discuss how structure–property relations can lead to superior micro- and micromesoporous carbon adsorbents for reactive adsorption toward high HMF yield. Finally, we provide an outlook for the field.

ChemInform Abstract: Recent Advances on the Lewis Acid‐Catalyzed Cascade Rearrangements of Propargylic Alcohols and Their Derivatives

AbstractReview: 71 refs.

Heterogeneous Lewis Acid Catalysts Workable in Water

Abstract The Lewis acidities of Nb2O5·nH2O, anatase TiO2, and Ti-deposited mesoporous silica (TDMS) in the presence of water have been studied to devise new catalytic systems for the environmentally benign production of chemicals. These Groups 4 and 5-based oxides exhibit high catalytic performance for Lewis acid-catalyzed reactions in aqueous media such as the conversion of glucose into 5-(hydroxymethyl)furfural (HMF), lactic acid production from pyruvaldehyde, the allylation of benzaldehyde with tetraallyltin, and the Mukaiyama–aldol condensation of benzaldehyde with 1-trimethylsilyloxycyclohexene. Lewis acid catalysis of these materials in water can be attributed to MOx unsaturated coordination spheres such as NbO4 and TiO4 terrahedra: they are not decomposed in water and water molecules interacting with such Lewis acid sites can be easily exchanged with nucleophilic reactants. Lewis acid-catalyzed reactions on TiO2 and TDMS revealed that Lewis acid sites on TDMS are quite distinct from those of TiO2 in catalysis.

Slow reactant-water exchange and high catalytic performance of water-tolerant Lewis acids.

(31)P nuclear magnetic resonance (NMR) spectroscopic measurement with trimethylphosphine oxide (TMPO) was applied to evaluate the Lewis acid catalysis of various metal triflates in water. The original (31)P NMR chemical shift and line width of TMPO is changed by the direct interaction of TMPO molecules with the Lewis acid sites of metal triflates. [Sc(OTf)3] and [In(OTf)3] had larger changes in (31)P chemical shift and line width by formation of the Lewis acid-TMPO complex than other metal triflates. It originates from the strong interaction between the Lewis acid and TMPO, which results in higher stability of [Sc(OTf)3TMPO] and [In(OTf)3TMPO] complexes than other metal triflate-TMPO complexes. The catalytic activities of [Sc(OTf)3] and [In(OTf)3] for Lewis acid-catalyzed reactions with carbonyl compounds in water were far superior to the other metal triflates, which indicates that the high stability of metal triflate-carbonyl compound complexes cause high catalytic performance for these reactions. Density functional theory (DFT) calculation suggests that low LUMO levels of [Sc(OTf)3] and [In(OTf)3] would be responsible for the formation of stable coordination intermediate with nucleophilic reactant in water.

Recent Advances on the Lewis Acid-Catalyzed Cascade Rearrangements of Propargylic Alcohols and Their Derivatives

Propargylic alcohols and their derivatives are important classes of organic compounds that can be easily accessible from terminal alkynes and aldehydes or ketones. They are attractive and have been extensively applied as synthetic intermediates in modern organic synthesis. Recent investigations on the chemistry of propargylic alcohols and their derivatives disclosed a variety of highly efficient Lewis acid-catalyzed cascade reactions based on Meyer–Schuster rearrangement of propargylic alcohols and [3,3] rearrangement of propargylic esters and propargyl vinyl ethers. A tremendous number of structurally versatile enones, carbocycles, and heterocycles have been constructed through these methodologies. These advances, including our recent researches in this field, are summarized in this review.

Corrigendum: Iron- and Bismuth-Catalyzed Asymmetric Mukaiyama Aldol Reactions in Aqueous Media

The authors found that sentences were corrupted and the cited references were incomplete in the second paragraph of the Introduction. This paragraph should read as follows. In Scheme 5, the compound in the middle of the 4th row should be labeled 3 te. In Scheme 6, 1 u and 3 ua should read 1 v and 3 va, respectively. The authors apologize for these mistakes. Catalytic asymmetric variants on the Mukaiyama aldol reaction were initiated by a report on chiral tin(II) Lewis acid-catalyzed reactions in 1990,3 and chiral boron,4 chiral titanium,5 and chiral zirconium6 Lewis acids followed. Since then, many chiral Lewis acids have been developed to target asymmetric Mukaiyama aldol reactions.7 On the other hand, “direct-type aldol reactions” have been reported, in which the reactions did not proceed through silicon enolates but rather through ketones or synthetic equivalents, which reacted as nucleophiles directly with aldehydes.8, 9 While silicon enolates have to be prepared (isolated) from ketones using stoichiometric amounts of bases and silicon sources in Mukaiyama aldol reactions, direct-type reactions give aldol adducts directly. Therefore, from an atom economical point of view, the latter has an advantage. At the present stage, however, nucleophiles that can be used in direct-type aldol reactions are limited to ketones and aldehydes in most cases.10 Furthermore, among them there are few examples of aromatic ketones or acyclic ketones using non-metal catalysts.11 Silicon enolates that can be applied to the Mukaiyama aldol reaction are derived not only from ketones and aldehydes but also from esters, amides, lactones, lactams, enones, unsaturated esters, unsaturated amides, and others. Therefore, from the standpoint of substrate generality, the Mukaiyama aldol reaction still has an advantage over the direct-type aldol reaction.

Three-Component Povarov Reaction–Heteroannulation with Arynes: Synthesis of 5,6-Dihydroindolo[1,2-a]quinolines

A reaction of 2-acyl substituted tetrahydroquinolines, prepared by Lewis acid-catalyzed three-component reaction of α-oxo aldehydes, anilines, and dienophiles, with in situ generated arynes afforded 5,6-dihydroindolo[1,2-a]quinolines in good to excellent yields.