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A protocol exploiting isocyanides as carbamoylating agents for the α‐C(sp3)‐H functionalization of cyclic ethers has been optimized via a combined visible light‐driven hydrogen atom transfer/Lewis acid‐catalyzed approach. The isocyanide substrate scope revealed an exquisite functional group compatibility (18 examples, with yields up to 99 %). Both radical and polar trapping, kinetic isotopic effect and real‐time NMR studies support the mechanistic hypothesis and provide insightful details for the design of new chemical processes involving the generation of oxocarbenium ions. [ABSTRACT FROM AUTHOR]

A BF3 ·OEt2-promoted facile synthesis of cyclic amidines (2-amino-1-pyrrolines) has been developed via the (3+2)-cycloaddition of cyanamides with donor-acceptor cyclopropanes (DACs). In addition to this, the protocol has been successfully extended to construct a dimerized amidine derivative and gram-scale synthesis with great efficiency. [ABSTRACT FROM AUTHOR]

Although the ability of Lewis acids to initiate oligomerisation or polymerisation of pyrroles and indoles is known, no reliable information was available on the structures of the complexes formed therewith. Using 1H NMR spectroscopy, an attempt has now been made to elucidate the structures of the complexes formed by the treatment of pyrroles and indoles with AlCl3. [ABSTRACT FROM AUTHOR]

Polyol esters are abundant bio‐based resources. Integration of polyol esters into the production chain of fine chemicals would reduce carbon emissions and improve the sustainability of the chemical industry. An efficient synthetic route to phenoxyethanols was developed through catalytic hydroxyethylation of phenols with ethylene glycol diacetate as the reagent. This method showed the potential of ethylene glycol diester as a safe and sustainable substitute for ethylene oxide, a useful but toxic reagent. A variety of phenoxyethanol esters were produced in high yield under simple catalytic conditions. Mechanistic studies revealed that the reaction underwent a neighboring group participation process. [ABSTRACT FROM AUTHOR]

This article discusses the synthesis of highly functionalized quinolines through a novel FeIII-catalyzed domino reaction. Quinolines have been widely used in pharmaceutical compounds and have shown various biological activities, including antifungal, antibacterial, and anti-inflammatory properties. The article presents the optimization of reaction conditions and explores the scope of the developed reaction. The FeIII-catalyzed domino reaction offers a cost-effective, environmentally friendly, and greener approach to synthesizing functionalized quinolines under mild conditions. [Extracted from the article]

Diphenyl carbonate is one of the raw materials used for the synthesis of polycarbonate, and its green and clean production is of great importance to the non-phosgene process for polycarbonate. The production of diphenyl carbonate by transesterification is its representative process route and is considered to be one of the typical examples of a green and sustainable process for chemicals. Since the discovery of the transesterification catalyst for diphenyl carbonate in the 1970s, researchers have been committed to improving its catalytic activity and selectivity and, correspondingly, the reaction engineering process. However, thermodynamic limitations, low activity, low selectivity, and limited stability have been bottlenecks that the transesterification catalyst has not been able to completely overcome, and the improvement of the catalyst is still ongoing. Therefore, this review takes the transesterification reaction of dimethyl carbonate and phenol as a model reaction and, based on a review of the progress in catalyst research on catalytic reaction processes, tries to clarify the structure–activity relationship between catalytic active sites and catalytic performance in homogeneous and heterogeneous catalytic processes and provides an overview of the progress in catalyst synthesis and modification. [ABSTRACT FROM AUTHOR]

The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water‐tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn‐ and Zr‐containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10‐MR medium pore zeolites (FER, MCM‐56, MEL, MFI, MWW), 12‐MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14‐MR extra‐large pore UTL zeolite. This review about Sn‐ and Zr‐containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances. [ABSTRACT FROM AUTHOR]

A microporous metal–organic framework {[Ni4(μ3−OH)2(d-2,4-cbs)2(H2O)4]·5H2O}n (Ni-CBS) with a stable Ni4(μ3–OH)2 core has been solvothermally synthesized by using an aspartate-derived tricarboxylic acid, H3(d-2,4-cbs). A tapered microrod-like surface morphology of Ni-CBS is observed via field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). Its crystallinity and thermal stability are analyzed using powder X-ray diffraction (PXRD) and thermogravimetric analysis (TGA), respectively. The nitrogen adsorption isotherm at 77 K validates the micron-size pores in the framework. The amine-functionalized framework is further utilized to study CO2 adsorption for a potent interaction between the framework and CO2 molecules with an isosteric heat of adsorption (Qst) value of 33.5 kJ mol–1 at zero loading. Further, the microporous nature of the framework is demonstrated through the encapsulation of various organic solvent molecules. With a high CO2 uptake value at room temperature (47.8 cm3g–1), Ni-CBS is found to be a competent heterogeneous catalyst for the formation of cyclic carbonates by fixing carbon dioxide chemically with epoxides of appropriate molecular dimensions. Furthermore, the catalytic behavior of Ni-CBS is compared with the previously reported isostructural Zn-CBS under solvent-free conditions, confirming more Lewis acid character of Zn-(II) over Ni-(II). [ABSTRACT FROM AUTHOR]

Abstract The incorporation of isolated Sn (IV) and Zr (IV) ions into silica frameworks is attracting widespread attention, which exhibits remarkable catalytic performance (conversion, selectivity, and stability) in a broad range of reactions, especially in the field of biomass catalytic conversion. As a representative example, the conversion route of carbohydrates into valuable platform and commodity chemicals such as lactic acid and alkyl lactates, has already been established. The zeotype materials also possess water‐tolerant ability and are capable to be served as promising heterogeneous catalysts for aqueous reactions. Therefore, dozens of Sn‐ and Zr‐containing silica materials with various channel systems have been prepared successfully in the past decades, containing 8 membered rings (MR) small pore CHA zeolite, 10‐MR medium pore zeolites (FER, MCM‐56, MEL, MFI, MWW), 12‐MR large pore zeolites (Beta, BEC, FAU, MOR, MSE, MTW), and 14‐MR extra‐large pore UTL zeolite. This review about Sn‐ and Zr‐containing metallosilicate materials focuses on their synthesis strategy, catalytic applications for diverse reactions, and the effect of zeolite characteristics on their catalytic performances.

Diphenyl carbonate is one of the raw materials used for the synthesis of polycarbonate, and its green and clean production is of great importance to the non-phosgene process for polycarbonate. The production of diphenyl carbonate by transesterification is its representative process route and is considered to be one of the typical examples of a green and sustainable process for chemicals. Since the discovery of the transesterification catalyst for diphenyl carbonate in the 1970s, researchers have been committed to improving its catalytic activity and selectivity and, correspondingly, the reaction engineering process. However, thermodynamic limitations, low activity, low selectivity, and limited stability have been bottlenecks that the transesterification catalyst has not been able to completely overcome, and the improvement of the catalyst is still ongoing. Therefore, this review takes the transesterification reaction of dimethyl carbonate and phenol as a model reaction and, based on a review of the progress in catalyst research on catalytic reaction processes, tries to clarify the structure–activity relationship between catalytic active sites and catalytic performance in homogeneous and heterogeneous catalytic processes and provides an overview of the progress in catalyst synthesis and modification.

Aryne insertions into the carbon‐iodine bond of heteroaryl iodides has been achieved for the first time. This novel reaction provides an efficient pathway for the synthesis of valuable building blocks 2‐iodoheterobiaryls from heteroaryl iodides and o‐silylaryl triflates in excellent regioselectivity. The copper(I) catalyst, which bears a N‐heterocyclic carbene (NHC) ligand, is essential to accomplish the reaction. Control reactions and DFT calculations indicate that the coordination of copper, as a Lewis acid, with nitrogen atoms of heteroaryl iodides mediates the insertion of arynes into heteroaryl carbon‐iodine bonds. [ABSTRACT FROM AUTHOR]

Cascade aza‐Piancatelli reaction and [3+3]/[4+2] cycloaddition reactions are carried out using the ideality principles of pot, atom, and step economy (PASE) synthesis. The reaction resulted in generation of octahydro‐4H‐cyclopenta[b]pyridin‐6‐one scaffolds. Moreover, octahydro‐5,7a‐epoxycyclopenta[cd]isoindol‐4‐one frameworks of gracilamine alkaloid and a novel decahydro‐1H‐dicyclopenta[cd,hi]isoindol‐6‐one were also realized in good yields with excellent regio‐ and diastereo‐selectivities. [ABSTRACT FROM AUTHOR]

Keywords: allylation; enol silane; one pot; alkylation; silyl triflates; Lewis acid catalysis; regioselectivity EN allylation enol silane one pot alkylation silyl triflates Lewis acid catalysis regioselectivity 2377 2389 13 07/14/23 20230801 NES 230801 Graph Allylation of ketones remains an active area of pursuit, with recent reports focusing upon the reaction of enol silanes, [1] enol acetates, [3] 1,3-dicarbonyls, [4] and simple unactivated ketones [6] with quasi-symmetrical allylic alcohols derived from chalcone. For example, a consistent color change from pale yellow to dark red or black was generally observed upon addition of TMSOTf to reaction mixtures containing allyl propionates, a change not observed when allyl propionate was absent; this color change may provide circumstantial evidence for the formation of the proposed carbocation. One-Pot Enol Silane Formation-Allylation of Ketones Promoted by Trimethylsilyl Trifluoromethanesulfonate While both allyl acetates and allyl propionates proved to be active carbocation precursors under the reaction conditions, allyl propionates provided consistently cleaner conversion to the desired product, and their use suppressed competing [3,3] and [1,3] rearrangements of the starting material. [Extracted from the article]

Hydrogen atom transfer (HAT) is one of the important class of radical reactions. Although extensive research into this elementary step has resulted in the discovery of many compounds capable of functioning as HAT reagents, synthetic methods available to control the stereoselectivity of the HAT process remains challenging. This mini review outlines how small molecule chiral HAT reagents and catalysts were used to achieve stereoselectivity (diastereoselectivity and enantioselectivity) in free radical reactions. The review also focuses on the recent surge in photoenzymatic catalysis to achieve efficient HAT reactions. [ABSTRACT FROM AUTHOR]

A visible‐light‐induced acyl radical conjugate addition to electron‐deficient alkenes with acylsilane was realized by merging photoredox and Lewis acid catalysis under mild reaction conditions. Various tri‐ and tetra‐substituted furans were obtained with good yield (up to 97%) from α,β‐unsaturated ketones. Based on the experimental results and spectral analysis, a possible catalytic cycle involving 1,4‐conjugate addition/ring‐closure/arylation sequence was proposed. Beyond that, 1,6‐acyl radical conjugate addition to para‐quinone methides was also accomplished to deliver a series of α‐aryl ketones by using this synergistic catalysis protocol. [ABSTRACT FROM AUTHOR]

We report a straightforward, metal-free, efficient protocol for the synthesis of 2-phenylnaphthalenes from 1-phenylethane-1,2-diols under mild conditions. In this strategy, 1,1,1,3,3,3-hexafluoro-2-propanol is used as a solvent that stabilizes the reaction intermediate. An in situ IR experiment revealed that the reaction proceeds through the formation of phenylacetaldehyde followed by a [4+2] Diels–Alder reaction. Several control experiments were performed to gain mechanistic insights into the reaction. [ABSTRACT FROM AUTHOR]

Compared to γ‐addition, the α‐addition of α‐branched β,γ‐unsaturated aldehydes faces larger steric hindrance and disrupts the π–π conjugation, which might be why very few examples are reported. In this article, a highly diastereo‐ and enantioselective α‐regioselective Mannich reaction of isatin‐derived ketimines with α‐, β‐ or γ‐branched β,γ‐unsaturated aldehydes, generated in situ from Meinwald rearrangement of vinyl epoxides, is realized by using chiral N,N′‐dioxide/ScIII catalysts. A series of chiral α‐quaternary allyl aldehydes and homoallylic alcohols with vicinal multisubstituted stereocenters are constructed in excellent yields, good d.r. and excellent ee values. Experimental studies and DFT (density functional theory) calculations reveal that the large steric hindrance of the ligand and the Boc (tButyloxy carbonyl) protecting group of imines are critical factors for the α‐regioselectivity. [ABSTRACT FROM AUTHOR]

3-Isothiocyanato oxindoles are a class of important building blocks which have been widely used in the synthesis of structurally diverse enantioenriched spirooxindoles. In this short review, it is attempted to cover the recent synthetic aspects of 3-isothiocyanato oxindoles participated cascade cyclizations in the last few years (i.e., from 2017 to 2022), with an emphasis on formal [3+2] cycloaddition reactions. 1 Introduction 2 Organocatalyzed Formal [3+2] Cycloaddition of 3-Isothiocyanato Oxindoles 3 Lewis Acid Catalyzed Formal [3+2] Cycloaddition of 3-Isothiocyanato Oxindoles 4 Conclusions [ABSTRACT FROM AUTHOR]

The Lewis acidic nature of both {[Zn4(µ3-OH)2(d-2,4-cbs)2(H2O)4].5H2O}n(Zn-CBS) and its ZnO nanostructures (ZnO_1, 3D microflower; ZnO_2, 3D polyhedron; and ZnO_3, 1D nanorod) was explored for the comparative study of the C–C and C-N bond forming reactions, such as Knoevenagel condensation, Friedel–Crafts alkylation and Strecker reaction, with various substrates. Notably, the nanorod (ZnO_3) is found to be an exceptionally efficient heterogeneous catalyst in comparison to its parent Zn-CBS for the Knoevenagel condensation reaction showing 100% conversion in 15 min with only 2 mol% catalyst in methanol at 25 °C. Similar catalytic results were obtained in the multicomponent Strecker reaction where ZnO_3 showed an enhanced catalytic activity in water as compared to Zn-CBS. However, for the Friedel–Crafts alkylation reaction, Zn-CBS was better than ZnO_3. These highly efficient catalysts are recyclable for three consecutive runs without any notable change in the catalytic activity. Their mechanism of action for all three reactions is also explained. [ABSTRACT FROM AUTHOR]

Recently, we presented a novel enantioselective multicomponent reaction of phthalazines, aldehydes and thiols accessing thioether‐substituted 1,2‐dihydronaphthalenes. Herein, a comprehensive investigation on the mechanism of this domino inverse electron‐demand (IEDDA)/thiol transfer reaction is disclosed. In particular, the origin of the stereochemical outcome has been rationalized, as well as structural requirement of the thiol component for an efficient transfer step. Detailed NMR spectroscopy studies uncover a competing reaction pathway resulting in N,S‐acetals. In addition, DFT computations illuminate the mechanism of the group transfer process and enable an explanation for the formation of the most dominant by‐product. The insights allow a direct prediction of suitable substrates for the reaction and provide the basis for further developments of novel stereoselective domino reactions. [ABSTRACT FROM AUTHOR]

A new Lewis acid promoted domino isocyanide insertion/5-exo-dig cyclization of readily available Strecker 3-component adducts to 4-substituted 5-aminoimidazole derivatives is herein reported. Despite their potential as relevant heterocyclic scaffolds in medicinal chemistry programs, this class of compounds is still underrepresented, with current synthetic strategies poorly efficient in terms of timing and yields. To this end, we show how the exploitation of unconventional reactivities of isocyanides, promoted by ytterbium-triflate, could represent a key resource to enable a fast and easy access to such an unexplored area of the chemical space. [ABSTRACT FROM AUTHOR]

Quinolizidine and azaphenalene alkaloids are common in nature and exhibit a pharmaceutical activity, which stirs up increased interest in expanding the range of methods for the synthesis of the corresponding derivatives. In this work, we attempted to adapt our previously presented method for the synthesis of tetrahydropyridines to the preparation of potential precursors for these heterocycles as a separate development of a necessary intermediate stage. To this end, we studied the reactions of β-styrylmalonates with N-protected cross-conjugated azatrienes in the presence of Sn(OTf)2. Moreover, the regioselectivity of the process involving unsymmetrically substituted azatrienes was estimated. The diene character of vinyltetrahydropyridines was studied in detail with the participation of PTAD. Finally, for the Ts-protected highly functionalized vinyltetrahydropyridines synthesized, a detosylation method to give new desired azadiene structures as precursors of the quinolizidine core was suggested. [ABSTRACT FROM AUTHOR]

A hyperresponsive tool to assess supramolecular catalysis, the cyclization of di‐epoxides into cyclic ethers is used to elucidate the difference between pnictogen‐bonding and Lewis acid catalysis systematically. For all stereoisomers, most tested catalysts follow the Baldwin rules. Brønsted acid and anion–π catalysis afford almost only Baldwin products. Lewis acids such as SbCl3, BF3 and BiCl3 give the poorest selectivity, with at least 50 % Baldwin (B) products for all stereoisomers. In clear contrast, optimized pnictogen‐bonding catalysts operating on the Sb(III) and the Sb(V) level give the fused anti‐Baldwin (A) bicycles as the main product of trans epoxides, independent of syn or anti relation of the two epoxides. In the cis series, Sb(III) pnictogen‐bonding catalysts afford BA products almost exclusively for syn diastereomers, while anti diastereomers give equal amounts of BA and AB products. Sb(V) pnictogen‐bonding catalysts show similarly special trends. These unique characteristics support that pnictogen‐bonding catalysis differs from Lewis acid catalysis and can arguably be defined as its non‐covalent counterpart, just like hydrogen‐bonding catalysis is understood and appreciated as the non‐covalent counterpart of Brønsted acid catalysis. Computational studies on the origin of anti‐Baldwin selectivity reveal Sb(V) catalysts with an introvert deep σ hole surrounded by an almost planar ring of ligands. Central pnictogen‐bond attraction against peripheral steric repulsion then forces the epoxide to break open. In contrast, transient antimony oxidation in cyclic intermediates accounts for the chemoselectivity of Sb(III) catalysts. Presumably due to insufficient accessibility of their σ holes, the activity of tetrel‐bonding catalysts is negligible. The division between powerful pnictogen‐bonding and irrelevant tetrel‐bonding catalysts does not exist with the respective orthodox Lewis acids and thus supports that σ‐hole and Lewis acid catalysis are not the same. [ABSTRACT FROM AUTHOR]

A Lewis acid-catalyzed [4 ​+ ​2] cycloaddition of 3-alkyl-2-vinylindoles with β,γ-unsaturated α-ketoesters has been established in the presence of Sc(OTf)3, which afforded a series of indole-containing pyran derivatives in generally good yields (up to 90% yield) with excellent diastereoselectivities (up to ​> 95:5 dr) under mild conditions. This approach not only enriches the chemistry of 3-alkyl-2-vinylindoles, but also has provided an atom-economic method for the synthesis of indole-containing pyran derivatives with potential bioactivity.

A Lewis acid‐catalyzed (3+2) cycloaddition of 2‐indolylmethanols with β,γ‐unsaturated α‐ketoesters was established, which afforded a series of cyclopenta[b]indoles in overall high yields (up to 98 %) with excellent diastereoselectivities (up to >95 : 5 dr). This reaction not only represents the first C3‐nucleophilic (3+2) cycloaddition of 2‐indolylmethanols, but also provides a good example for (2+n) cycloaddition of β,γ‐unsaturated α‐ketoesters, which will add new contents to the chemistry of 2‐indolylmethanols. In addition, this approach provides an atom‐economic and useful method for the construction of biologically important cyclopenta[b]indole scaffold. [ABSTRACT FROM AUTHOR]

In the present study, the influence of adding cerium oxide to NiMo/Al2O3 hydrodesulfurization (HDS) catalysts was herein analyzed through the impregnation of cerium sulfate at the surface of an Al2O3 support obtained by a sol–gel method at two different Ce contents (1 and 5 mol% as CeO2). The cerium-containing Al2O3 supports were then impregnated with Ni(NO3)2 and (NH4)6Mo7O24 precursors in aqueous solutions at pH 7 or pH 9 before being dried at 120 °C for 4 h and finally calcined under air at 400 °C for 4 h. The as-obtained NiMo/Ce–Al2O3 catalysts were characterized at their oxide state using UV–Vis diffuse reflectance, Raman and Infrared spectroscopies after each preparation step. Catalysts were also characterized at the sulfide state by pyridine adsorption followed by infrared spectroscopy. The sulfide catalysts were then evaluated in the hydrodesulfurization of dibenzothiophene (DBT). Results show that the pH of impregnation used influences more the final HDS activity than the amount of Ce with an optimum observed using 1 mol % and a pH of impregnation of 9. The activity achieved is then 62% higher than for a NiMo/Al2O3 reference catalyst. The analysis of both Raman and UV–Vis spectroscopy results show that impregnation under basic conditions help to maximize the dispersion of the CeO2 phase onto the alumina support improving substantially the final HDS activity. [ABSTRACT FROM AUTHOR]

A Ti(Oi‐Pr)4 promoted 5‐ or 6‐endo‐trig cyclisation to make nitrogen heterocycles is presented. The utilisation of HFIP as a key solvent enables the stereoselective preparation of di‐ & tri‐substituted pyrrolidines and piperidines while forming a new C−C bond at the same time. The process is triggered by a cationic intermediate generated from an allylic or benzylic alcohol and leads to the simultaneous generation of both a C−C and a C−N bond in a single step. Notably, either 2,3‐trans‐ or 2,3‐cis‐substituted heterocycles can be obtained by using a nucleophilic amine bearing different substituents. Lastly, the stereoselective synthesis of enantiopure products was achieved by using readily available enantiopure acyclic starting materials. [ABSTRACT FROM AUTHOR]

We report a formal carbon–carbon (C−C) bond insertion via the reaction of secondary benzylic halides (fluorides, chlorides, and bromides) with α‐diazo esters catalyzed by Lewis acid catalysts. Secondary benzylic halides underwent elongation to afford α,β‐diaryl‐β‐haloesters diastereoselectively. Density functional theory calculation revealed that the present formal C−C bond insertion was the result of Lewis acid‐promoted cleavage and the re‐formation of a carbon–halogen bond and that the aryl‐migration step determined the diastereoselectivity. Various diarylmethyl halides and α‐diazo esters were applicable to this reaction system. In addition, ring expansion in cyclic benzylic chlorides was accomplished. [ABSTRACT FROM AUTHOR]

A highly enantioselective tandem Pudovik addition/[1,2]‐phospha‐Brook rearrangement of α‐alkynylketoamides with diarylphosphine oxides was achieved with a N,N′‐dioxide/ScIII complex as the catalyst. This protocol features broad substrate scope, high regio‐ and enantioselectivity, and good functional‐group compatibility, providing a straightforward route to various trisubstituted allenes with a diarylphosphinate functionality in good yields with high enantioselectivities (up to 97 % yield, 96 % ee). Control experiments and theoretical calculations revealed that a synergistic effect of the counterion and water was critical for the regio‐ and enantioselective protonation after [1,2]‐phospha‐Brook rearrangement. The synthetic utility of this methodology was demonstrated by the conversion of products into complex bridged polycyclic architectures through intramolecular dearomatizing arene/allene cycloaddition. [ABSTRACT FROM AUTHOR]

A new and efficient method for preparation of quinazoline‐2,4‐diones by tandem reaction of isatins with aryl/alkyl amines via oxidative rearrangement in the presence of Lewis acid/TBHP is described. This method offers a new approach with wide substrate scope for preparation of quinazoline‐2,4‐diones, in highyields under mild conditions. [ABSTRACT FROM AUTHOR]

A protocol exploiting isocyanides as carbamoylating agents for the α-C(sp 3 )-H functionalization of cyclic ethers has been optimized via a combined visible light-driven hydrogen atom transfer/Lewis acid-catalyzed approach. The isocyanide substrate scope revealed an exquisite functional group compatibility (18 examples, with yields up to 99 %). Both radical and polar trapping, kinetic isotopic effect and real-time NMR studies support the mechanistic hypothesis and provide insightful details for the design of new chemical processes involving the generation of oxocarbenium ions., (© 2024 The Author(s). Chemistry - A European Journal published by Wiley-VCH GmbH.)

A catalytic [3+2]-cycloaddition using Sc(OTf)3 as a Lewis acid catalyst is developed. This catalytic 1,3-dipolar cycloaddition dia-stereoselectively transforms diazoacetoacetate enones and N -aryl nitrones into highly functionalized isoxazolidines bearing three contiguous chiral centers. The feasibility of the uncatalyzed 1,3-dipolar cycloaddition is postulated by DFT calculations and substantiated experimentally. [ABSTRACT FROM AUTHOR]

Density functional theory calculations with the M06-2X exchange–correlation functional have been performed to explore the Diels–Alder reaction between 2,5-DMF and ethylene as well as to compare the uncatalyzed reaction to the one catalyzed by the AlCl3 Lewis acid. The uncatalyzed reaction corresponds to a normal electron-demand (NED) mechanism where ethylene is an electron acceptor and 2,5-DMF plays the role of electron donor. This reaction presents a low polar character, its kinetics is little impacted by the solvent dielectric constant, and the formation of the two new σ bonds occurs through a one-step synchronous process. When the LA interacts with ethylene, forming a π-complex, it enhances its acceptor character, further favoring the NED mechanism, which is accompanied by a reduction of the free energy of the transition state. On the other hand, when AlCl3 is complexed by 2,5-DMF, the inverse electron-demand (IED) mechanism is favored, with ethylene playing the role of the donor. Within both NED and IED mechanism, the LA-catalyzed reaction takes place via a one-step asynchronous process. In addition, it is highly polar, so that the activation barrier decreases with the solvent polarity. Moreover, the calculations have evidenced that the LA forms stable complexes with any of the reactants so that the gain on the activation barrier amounts to 9–12 kcal mol−1 for the NED mechanism and to 3–9 kcal mol−1 for the IED one and that the formation of Al2Cl6 dimers impacts the different equilibria. Finally, the decrease of the activation barrier goes in pair with the reduction of the HOMO–LUMO gap, with the greatest decrease recorded when the LA interacts with ethylene according to the NED mechanism. [ABSTRACT FROM AUTHOR]

Diazo compounds have been largely used as carbene precursors for carbene transfer reactions in a variety of functionalization reactions. However, the ease of carbene generation from the corresponding diazo compounds depends upon the electron donating/withdrawing substituents either side of the diazo functionality. These groups strongly impact the ease of N2 release. Recently, tris(pentafluorophenyl)borane [B(C6F5)3] has been shown to be an alternative transition metal‐free catalyst for carbene transfer reactions. Herein, a density functional theory (DFT) study on the generation of carbene species from α‐aryl α‐diazocarbonyl compounds using catalytic amounts of B(C6F5)3 is reported. The significant finding is that the efficiency of the catalyst depends directly on the nature of the substituents on both the aryl ring and the carbonyl group of the substrate. In some cases, the boron catalyst has negligible effect on the ease of the carbene formation, while in other cases there is a dramatic reduction in the activation energy of the reaction. This direct dependence is not commonly observed in catalysis and this finding opens the way for intelligent design of this and other similar catalytic reactions. [ABSTRACT FROM AUTHOR]

A highly diastereoselective bidirectional C(sp3)−H bond functionalization of piperazine compounds, triggered by a Lewis acid catalyzed sequential hydride shift/cyclization process, is reported. Catalysts and ligands are key factors that control the diastereoselectivity of the reaction. The reaction affords the product with good yield and high diastereoselectivity. Detailed investigation of the reaction mechanism reveals that the energy barrier between the cis products and trans products results in the diastereoselectivity of the reaction. The trans products, which have higher energy and which are generated from the cis products, act as intermediate products. [ABSTRACT FROM AUTHOR]

Quinolizidine and azaphenalene alkaloids are common in nature and exhibit a pharmaceutical activity, which stirs up increased interest in expanding the range of methods for the synthesis of the corresponding derivatives. In this work, we attempted to adapt our previously presented method for the synthesis of tetrahydropyridines to the preparation of potential precursors for these heterocycles as a separate development of a necessary intermediate stage. To this end, we studied the reactions of β-styrylmalonates with N-protected cross-conjugated azatrienes in the presence of Sn(OTf)2. Moreover, the regioselectivity of the process involving unsymmetrically substituted azatrienes was estimated. The diene character of vinyltetrahydropyridines was studied in detail with the participation of PTAD. Finally, for the Ts-protected highly functionalized vinyltetrahydropyridines synthesized, a detosylation method to give new desired azadiene structures as precursors of the quinolizidine core was suggested.

In the present work, we explored Lewis acid catalysis, via FeCl 3 , for the heterogeneous surface functionalization of cellulose nanofibrils (CNFs). This approach, characterized by its simplicity and efficiency, facilitates the amidation of nonactivated carboxylic acids in carboxymethylated cellulose nanofibrils (c-CNF). Following the optimization of reaction conditions, we successfully introduced amine-containing polymers, such as polyethylenimine and Jeffamine, onto nanofibers. This introduction significantly enhanced the physicochemical properties of the CNF-based materials, resulting in improved characteristics such as adhesiveness and thermal stability. Reaction mechanistic investigations suggested that endocyclic oxygen of cellulose finely stabilizes the transition state required for further functionalization. Notably, a nanocomposite, containing CNF and a branched low molecular weight polyethylenimine (CNF-PEI 800), was synthesized using the catalytic reaction. The composite CNF-PEI 800 was thoroughly characterized having in mind its potential application as coating biomaterial for medical implants. The resulting CNF-PEI 800 hydrogel exhibits adhesive properties, which complement the established antibacterial qualities of polyethylenimine. Furthermore, CNF-PEI 800 demonstrates its ability to support the proliferation and differentiation of primary human osteoblasts over a period of 7 days.

An easy and efficient route to obtain 2-amino-4,5-dihydrothiophenes is presented. A formal (3+2)-cycloaddition of donor–acceptor cyclopropanes and ammonium thiocyanate catalyzed by Yb(OTf)3 delivers the desired products in good to excellent yields. A broad range of functional groups is tolerated during this process. [ABSTRACT FROM AUTHOR]

3-Aryloxindole derivatives were synthesized through a Friedel–Crafts-type cyclization. The reaction was catalyzed by a trimethylsilyl tricyanopalladate complex generated in situ from trimethylsilyl cyanide and Pd(OAc)2. Wide varieties of diethyl phosphates derived from N -arylmandelamides were converted almost quantitatively into oxindoles. When N , N -dibenzylamide was used instead of an anilide substrate, a benzo-fused δ-lactam was obtained. An oxindole product was subjected to substitution reactions to afford 3,3-diaryloxindoles with two different aryl groups. [ABSTRACT FROM AUTHOR]

A three-component reaction involving in situ generation of propargylureas and subsequent Zn(OTf)2-mediated cyclocondensation with a primary amine yielded trisubstituted 2-aminoimidazoles. These findings are in contrast to the previously reported base-promoted unimolecular cyclization of propargylureas (leading to 2-imidazolones) and extend the range of Lewis acid-catalyzed azole syntheses based on N-carbonyl propargylamines.

7-Allylindolines are valuable synthons for designing biologically active molecular libraries. Lewis acid catalyzed amino-Claisen rearrangement provides a one pot synthetic entry to these heteroarenes. In this context, Zinc chloride (ZnCl2)–N,N-dimethylformamide system efficiently catalyzed amino-Claisen rearrangements of 1-N-allylindolines to 7-allylindolines. The rearrangement is influenced by stereoelectronic effects of substituents present in 1-N-allylindolines. The substrates containing electron donating functionalities underwent rearrangement at lower temperature than substrates with electron withdrawing functional groups. The regioselectivity of the process is governed by the substitution pattern on allyl moiety in 1-N-allylindoline as well as ZnCl2 catalyst loading in the reaction system.

Density functional theory (DFT) was utilized to understand how bismuth(III) salts (BiX3) achieve greatest activation of organic Lewis bases in a catalytic reaction. It is reported in the literature that the BiX3 reactivity originates from its low lying Bi−X σ* orbital. In contrast to this belief, we will show here that for BiX3 to effectively serve as a catalyst, a p orbital of bismuth needs to be involved in activating organic substrates. [ABSTRACT FROM AUTHOR]

Environment pollution is causing serious human health issues and forest deterioration. Methyl mercaptan is a malodorous gaseous pollutant, which is a by product of sewage treatment plants, pulp plants, petrochemical plants, agrochemicals, and some pharmaceutical products. A long term exposure to methyl mercaptan may lead to adverse effects on central nervous system and cardiovascular system. The pharmaceutical industries are devoting significant efforts to develop process by using green solvents like water, and develop solvent‐free reactions. This will help to develop green, sustainable methods for the synthesis of API and reduce the manufacturing cost. A ZnCl2 catalyzed solvent‐free, one‐pot process for the synthesis of ranitidine and quenching of hazardous waste methyl mercaptan gas to a useful product have been developed. [ABSTRACT FROM AUTHOR]

Allylic ethers of kojic acid undergo Claisen rearrangement with catalysis by zinc triflate to give the corresponding C-allylated kojic acids in moderate to good yields.

A novel organoantimony complex of 6‐cyclohexyl‐6,7‐dihydrodibenzo[c,f] [1,5]azastibocin‐12(5H)‐yl nitrate (2) was synthesized and systematically characterized by techniques such as NMR spectra, TG‐DSC, and X‐ray diffraction. It was found that the complex 2 exhibits relatively strong Lewis acidity (3.3 < Ho ≤ 4.8) and could be employed as a water tolerant Lewis acid catalyst for the synthesis of synthetically valuable benzimidazole derivatives starting from aldehydes and arylenediamines. This catalytic system shows excellent tolerance toward a wide variety of functional groups, such as methyl, methoxyl, fluoro, chloro, bromo, nitro, cyan, trifluoromethyl, 1‐naphthaldehyde, furfural and n‐butyl, together with facile reusability in 5 times scale enlarged synthesis. [ABSTRACT FROM AUTHOR]

The utility of (C6F5)3B(OH2) as catalyst for the simple and environmentally benign synthesis of oligosiloxanes directly from hydrosilanes, is reported. This protocol offers several advantages compared to other methods of synthesizing siloxanes, such as mild reaction conditions, low catalyst loading, and a short reaction time with high yields and purity. The considerable H2O-tolerance of (C6F5)3B(OH2) promoted a catalytic route to disiloxanes which showed >99% conversion of three tertiary silanes, Et3SiH, PhMe2SiH, and Ph3SiH. Preliminary data on the synthesis of unsymmetrical disiloxanes (Si-O-Si') suggests that by modifying the reaction conditions and/or using a 1:1 combination of silane to silanol the cross-product can be favored. Intramolecular reactions of disilyl compounds with catalytic (C6F5)3B(OH2) led to the formation of novel bridged siloxanes, containing a Si-O-Si linkage within a cyclic structure, as the major product. Moreover, the reaction conditions enabled recovery and recycling of the catalyst. The catalyst was re-used 5 times and demonstrated excellent conversion for each substrate at 1.0 mol% catalyst loading. This seemingly simple reaction has a rather complicated mechanism. With the hydrosilane (R3SiH) as the sole starting material, the fate of the reaction largely depends on the creation of silanol (R3SiOH) from R3SiH as these two undergo dehydrocoupling to yield a disiloxane product. Generation of the silanol is based on a modified Piers-Rubinsztajn reaction. Once the silanol has been produced, the mechanism involves a series of competitive reactions with multiple catalytically relevant species involving water, silane, and silanol interacting with the Lewis acid and the favored reaction cycle depends on the concentration of various species in solution.

Aluminum–magnesium oxides are excellent catalysts for the thiolation of methanol with H2S. The substitution of the alcohol OH with SH groups requires balanced Lewis acid and base sites. This is achieved by varying the aluminum and magnesium concentrations in the mixed oxide. The highest rate and selectivity was obtained for equal concentrations. [ABSTRACT FROM AUTHOR]