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The development of sustainable, functional-group-tolerant catalysis is highly significant from the perspectives of safety, user-friendliness, and cost-effectiveness. We report herein the triple hydrogen-bonding donor activator N -triflyl phosphoric triamide (N -TPT ) for the synergistic Brønsted acid aquacatalysis of multicomponent allylation 'on-water'. The reaction demonstrated remarkable efficiency in converting polar diol substrate, such as 1,3-dihydroxyacetone, into α-tertiary amine derivative incorporating homoallylic amine functionalities using bulk water as the reaction medium. The single crystal X-ray structure and control experiments highlighted the crucial role of multiple hydrogen bonds in enabling this aqueous reaction. [ABSTRACT FROM AUTHOR]

The present study describes the synthesis of various bioactive compounds, including bis‐coumarins, bis‐lawsones, bis‐dimedones, and bis‐indolylmethanes, using a novel catalytic system called "Brønsted acid saponin combined catalyst" (BASapC). The BASapC was formed by combining p‐toluenesulfonic acid (PTSA) and saponin in an aqueous medium. The prepared BASapC proved to be effective in facilitating cascade‐type Knoevenagel–Michael addition reactions between various aromatic aldehydes with 4‐hydroxycoumarin, lawsone, dimedone, or indole at 80 °C. In the BASapC system, PTSA acted as a powerful Brønsted acid, activating reactants, whereas saponin served as a natural surfactant, enhancing the solubility of organic compounds in water. This catalytic approach established a straightforwardness and robustness of diversity‐oriented synthesis (DoS), delivering the desired products with good to excellent yields. Additionally, the BASapC exhibited recyclability for at least four cycles without significant loss of activity. [ABSTRACT FROM AUTHOR]

Brønsted acid catalyzed intramolecular allylic substitution reaction of secondary and tertiary allylic alcohols has been developed. A variety of 2-vinylchromans were efficiently prepared in moderate to excellent yields. The given method features wide substrate scope, operational simplicity, and mild, metal-free reaction conditions. The practicability of the method was demonstrated by a gram-scale reaction and further derivations of the product. Preliminarily studies on a catalytic asymmetric reaction were also undertaken. [ABSTRACT FROM AUTHOR]

In order to solve the problem of the low efficiency of lactose hydrolysis using traditional metal–organic frameworks (MOFs) nanozymes, Brønsted acid active sites (-COOH) were firstly introduced into Fe-MIL-101 nanozymes to enhance the lactose hydrolysis activity of MOFs bearing Lewis acid sites in this study. When compared to Fe-MIL-101, Fe-MIL-101-COOH exhibited improved catalytic performance, showing a lactose conversion rate of up to 78%. Our experiments suggested that this enhancement could be attributed to the synergistic effect between the Brønsted acidic COOH groups and Lewis acidic Fe clusters. Furthermore, Fe-MIL-101-COOH displayed good stability and reusability with no significant loss in catalytic activity observed after at least five consecutive cycles. Our results showed that the activity of Fe-MIL-101-COOH with Brønsted acid active sites was better than that of Fe-MIL-101. Fe-MIL-101-COOH could be applied to the hydrolysis of lactose in milk powder and the conversion rate of lactose was higher than 48%. This study provided support for the application of MOFs nanozymes in lactose catalytic conversion. [ABSTRACT FROM AUTHOR]

[Display omitted] Non-oxidative intercalation of graphite avoids damage to graphene lattices and is a suitable method to produce high-quality graphene. However, the yield of exfoliated graphene is low in this process due to the poor delamination efficiency of guest species. In this study, a Brønsted acid intercalation protocol is developed involving polyoxometalate (POM) clusters (H 6 P 2 W 18 O 62) as guests and intercalation of graphite is realized at the sub-nanometer scale. Theoretical simulation based on DFT elucidates the stepwise intercalation mechanism of Brønsted acid molecules and clusters. Unlike common molecules/ionic guests, intercalation of POM clusters induces large expansion and extensive donor–acceptor interactions among graphite interlayers. This significantly weakens the van der Waals forces and promotes exfoliation efficiency of graphene layers. The exfoliated graphene possesses outstanding features of large lateral size, thin thickness, and high purity, and shows excellent performance as the anode for high power sodium-ion batteries. This work proffers a new pathway toward non-oxidative intercalation of graphite for large-scale production of graphene. [ABSTRACT FROM AUTHOR]

A mechanochemistry approach is developed for regioselective synthesis of functionalized dihydropyrido[2,3‐d]pyrimidines by milling propargylic alcohols and 6‐aminouracils with HFIP/p‐TsOH. In the case of tert‐propargyl alcohols, this [3+3] cascade annulation proceeded through allenylation of uracil followed by a 6‐endo trig cyclization. With sec‐propargyl alcohols, the reaction furnished the propargylation of uracil. This atom economy ball milling reaction allows access to a broad range of dihydropyrido[2,3‐d]pyrimidine derivatives in excellent yields. We demonstrated the gram scale synthesis of 3 g and post‐synthetic modifications to effect the cyclization of 5 to 6. [ABSTRACT FROM AUTHOR]

The chemical space of chiral Brønsted acid catalysts is defined by quantity and complexity, reflecting the diverse synthetic challenges confronted and the innovative molecular designs introduced. Here, we detail how this successful outcome is a powerful demonstration of the benefits of utilizing both local structure searches and a comprehensive understanding of catalyst performance for effective and efficient exploration of Brønsted acid properties. In this concept article we provide an evolutionary overview of this field by summarizing the approaches to catalyst optimization, the resulting structures, and functions. [ABSTRACT FROM AUTHOR]

An alternative approach to synthesize bis‐indolylmethanes (BIMs) via a unique p‐toluenesulfonic acid (PTSA) catalyzed dual Csp3−Csp2 bond‐breaking reaction has been reported here. In the reported protocol, 1,3,5‐trimethoxybenzene (TMB), an electron‐rich and sterically bulky arene, acts as a carbon‐based leaving group which can be recovered after the completion of the reaction. In this process, several BIMs of various indole derivatives can be synthesized from symmetrical triarylmethanes (TRAMs) containing bis‐TMB motifs. By modifying the reaction conditions, we could control the sequential bond cleavage of two Csp3−Csp2 bonds in starting TRAM. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive overview of various methods for the synthesis of substituted naphthalene derivatives. Naphthalene is a versatile organic compound with applications in materials chemistry, electronics, and medicine. The synthesis of naphthalene involves metal-catalyzed reactions, such as palladium-catalyzed carboannulation, and yields derivatives with diverse substituents. These derivatives have medicinal importance and exhibit a wide range of therapeutic activities. The article discusses different metal-catalyzed reactions, their mechanisms, and examples of reactions. It also highlights the need for more environmentally friendly approaches to naphthalene synthesis. [Extracted from the article]

Electron-rich heteroaromatics, such as furan, thiophene and pyrrole, as well as their benzo-condensed derivatives, are of great interest as components of natural products and as starting substances for various products including high-tech materials. Although their reactions with Brønsted and Lewis acids play important roles, in particular as the primary step of various transformations, they are often disregarded and mechanistically not understood. The present publication gives a first overview about this chemistry focusing on the parent compounds. It comprises reactions with strong Brønsted acids forming adducts that can undergo intramolecular proton and/or substituent transfer reactions, ring openings or ring transformations into other heterocycles, depending on their structure. Interactions with weak Brønsted acids usually initiate oligomerizations/polymerizations. A similar behaviour is observed in reactions of these heteroaromatics with Lewis acids. Special effects are achieved when the Lewis acids are activated through primary protonation. Deuterated Brønsted acids allow straight forward deuteration of electron-rich heteroaromatics. Mercury salts as extremely weak Lewis acids cause direct metalation in a straight forward way replacing ring H-atoms yielding organomercury heterocycles. This review will provide comprehensive information about the chemistry of adducts of such heterocycles with Brønsted and Lewis acids enabling chemists to understand the mechanisms and the potential of this field and to apply the findings in future syntheses. [ABSTRACT FROM AUTHOR]

Fluorescent tiny molecules that are resistant to acid have long been the center of interest. The nitrogen atoms on benzyl cyanide were sp hybridized, while the two nitrogen atoms at pyrimidine were sp2 hybridized in the primary structure that we constructed. With the addition of a protonic acid (H2SO4, CH3SO3H, and HF), the nitrogen atoms at acridine underwent sp3 hybridization, which caused the hydrogen protons to interact with the three types of nitrogen atoms to varying degrees. This distribution of the electron cloud density led to a decrease in fluorescence emission. Furthermore, Gaussian 09 software and DFT calculations were used to model its orbital conformation, which is the highest occupied molecular orbital—lowest unoccupied molecular orbital (HOMO–LUMO). Furthermore, its crystal structure was assigned to the orthorhombic system with stronger non-homogeneity (a = 8.9160 (4) Å, b = 44.289 (3) Å, c = 9.6131 (7) Å, α = 90°, β = 90°, γ = 90°, V = 3796.0 (4) Å3, z = 4, Dc = 1.244 g/cm3). [ABSTRACT FROM AUTHOR]

A Brønsted acid-catalyzed regioselective intramolecular hydroalkoxylation is described. This reaction proceeds via a carbocation intermediate and enables the preparation of 1,1,1'-trisubstituted tetrahydropyran derivatives under mild conditions using catalytic triflic acid (TfOH) and hexafluoroisopropanol (HFIP) as a mediator. [ABSTRACT FROM AUTHOR]

This article presents a new method for synthesizing α-quaternary carbaldehydes through the chemoselective House-Meinwald rearrangement of trisubstituted epoxides. The authors used Brønsted acids as catalysts and identified optimal reaction conditions. The method allows for the synthesis of various carbaldehydes and has been validated for stereospecific reactions. The authors suggest that this method could be useful in the total synthesis of natural products. [Extracted from the article]

In this paper, rare earth tailings catalysts with different amounts of Mn modification were prepared by hydrothermal method, and the effects of Mn modification on the physical and chemical properties of rare earth tailings catalysts and the mechanism of surface thermal stability reaction were investigated by means of characterization, such as XRD, BET, NH3-TPD, H2-TPR, and infrared spectroscopy. The experiments showed that Mn modification of rare earth tailings under hydrothermal conditions allowed the synthesis of low-temperature wide-window (50 °C ~ 300 °C) catalysts. The best catalytic activity was achieved within the Mn-5% catalyst, which was above 85%. The results showed that Mn interacted with Fe/Ce elements in the rare earth tailings under hydrothermal conditions to improve the specific surface area and acid type and quantity of the rare earth tailings. In a mechanistic study of the surface thermal stability reaction during catalysis carried out by the Mn-5% catalyst, it was concluded that a large amount of Brønsted acid existed in the catalyst and acted as a reactive substance in the low-temperature section to mainly adsorb the NH4+ species, promoting the efficiency of low-temperature catalytic. Meanwhile the unstable nitrite species produced by hydrothermal Mn modification can react with NH3 adsorbed on the catalyst surface to enhance the low temperature catalytic capacity. [ABSTRACT FROM AUTHOR]

Brønsted acid mediated [3+2] cycloaddition of coumarin‐based enamines with 3‐ylidene oxindoles generated in situ from 3‐hydroxy‐3‐aroylmethyl oxindoles enabled the synthesis of polyheterocyclic compounds with a pyrrolocoumarin core structure in a highly regioselective manner. The synthetic procedure is highly efficient and metal‐free, and no chromatographic purification of the products is required. The chromenopyrrole derivatives bearing an oxindole moiety formed as rapidly interconverting rotamers. [ABSTRACT FROM AUTHOR]

4‐Aryl‐1H‐isochromene derivatives have been successfully synthesized by Brønsted acid‐catalyzed pinacol rearrangement/intramolecular cyclization of the substituted 1‐(2‐(hydroxymethyl)phenyl)‐2‐arylethane‐1,2‐diols. The reaction generally proceeded with low catalyst loading of trifluoromethanesulfonic acid (5 mol%) for short reaction times (10‐20 min) to furnish the desired 4‐aryl‐1H‐isochromenes which were subsequently hydrogenated to 4‐aryl‐isochromans with up to 90 % yield. Moreover, oxidation of the resulting 4‐aryl‐isochroman provided the desired 4‐aryl‐isochroman‐1‐one in good yield. [ABSTRACT FROM AUTHOR]

Developing a highly efficient catalytic system for the transformation of benzhydrol to simultaneously form diphenylmethane and diphenyl ketone is an attractive strategy in modern organic synthesis. In this work, acidic mesoporous Beta (H‐MBeta) zeolite successfully catalyzed the dismutation of the benzhydrol to yield equivalent amounts of diphenylmethane and diphenyl ketone under mild conditions. Combining X‐ray diffraction, N2‐adsorption, ammonia temperature programmed desorption, pyridine‐adsorbed infrared spectra, scanning electron microscopy and transmission electron microscopy, it was found that, compared to MBeta, H‐MZSM‐5 and USY zeolite catalysts, the abundant Brønsted acidic sites on the external surface of H‐MBeta are responsible for its superior catalytic performance. [ABSTRACT FROM AUTHOR]

Biorefinery of flavonoid aglycones by natural deep eutectic solvents (NADESs) is a green approach for the valorization of agro-food wastes. Using rutin/quercetin as a model system, this work studies the role of Bronsted acids in deglycosylation of flavonoid glycosides and the sustainable approach to producing aglycone-rich extracts by acidic NADESs. Different NADESs were tested, and the effects of Bronsted acids in catalysis and Hammett acidities were determined. The deglycosylation kinetics of rutin in the choline chloride-citric acid was measured and followed a first-order model with a half-life time (t1/2) of 0.16 h at 90 °C and an activation energy (Ea) of 140.3 kJ mol-1. A two-step one-pot approach was valid to produce quercetin-rich extracts from Sophora japonica buds waste. The quercetin-to-rutin ratio in the acidic NADES extracts was adjustable by changing the heating time. The acidic NADES of ChCl-Citric and quercetin-rich extracts showed low cytotoxicity to Caco-2 cells with EC50 greater than 2000 mg L-1, and the cytotoxicity was mainly determined by citric acid. The study provides a new perspective for the valorization of bioproducts into ready-to-use flavonoid aglycone-rich extracts using acidic NADES. [ABSTRACT FROM AUTHOR]

Electron-rich heteroaromatics, such as furan, thiophene and pyrrole, as well as their benzo-condensed derivatives, are of great interest as components of natural products and as starting substances for various products including high-tech materials. Although their reactions with Brønsted and Lewis acids play important roles, in particular as the primary step of various transformations, they are often disregarded and mechanistically not understood. The present publication gives a first overview about this chemistry focusing on the parent compounds. It comprises reactions with strong Brønsted acids forming adducts that can undergo intramolecular proton and/or substituent transfer reactions, ring openings or ring transformations into other heterocycles, depending on their structure. Interactions with weak Brønsted acids usually initiate oligomerizations/polymerizations. A similar behaviour is observed in reactions of these heteroaromatics with Lewis acids. Special effects are achieved when the Lewis acids are activated through primary protonation. Deuterated Brønsted acids allow straight forward deuteration of electron-rich heteroaromatics. Mercury salts as extremely weak Lewis acids cause direct metalation in a straight forward way replacing ring H-atoms yielding organomercury heterocycles. This review will provide comprehensive information about the chemistry of adducts of such heterocycles with Brønsted and Lewis acids enabling chemists to understand the mechanisms and the potential of this field and to apply the findings in future syntheses.

We present a rapid (0.25–1 h), method to produce functionalised allylsilanes from readily available vinylsilanes. Employing a Brønsted acid catalysed dehydration as the key step, allylsilanes are produced in good yields (22–98%) and, in most cases, as a single geometric isomer. Furthermore, a possible allylation‐Cope pathway was discovered for certain substrates and attempts to optimise this are described. [ABSTRACT FROM AUTHOR]

This study reports the first chemoenzymatic dynamic kinetic resolution (DKR) of racemic sec‐alcohols by simultaneously using immobilized lipase and aqueous sulfuric acid as catalysts for kinetic resolution and racemization, respectively. The nanoparticle‐stabilized phase separation in a Pickering emulsion enabled the use of these inherently incompatible catalysts in a single vessel. The racemization reaction in the aqueous sulfuric acid solution significantly suppressed the dehydrative side reactions that form alkenes and dimeric ethers, which are often observed in racemization using Brønsted/Lewis acids or oxovanadium compounds in organic solvents. The efficacy of the Pickering emulsion was confirmed by the significantly lower catalytic performance in DKR without emulsification. This method achieved high yields and high optical purities in the production of a wide range of sec‐alcohols. [ABSTRACT FROM AUTHOR]

An effective bifunctional Pd/SiO 2 -Al 2 O 3 -30 catalyst was synthesized for the selective hydrogenation-etherification of furfural to furfuryl ether and exhibited 86.2% 2-(isopropoxymethyl)furan yield with the synergistic catalysis of Pd particles and Brønsted–Lewis acid sites. [Display omitted] • An effective bifunctional Pd/SiO 2 -Al 2 O 3 -30 catalyst was synthesized successfully. • The catalyst exhibited 86.2% 2-(isopropoxymethyl)furan yield. • The incorporation of Si suppressed the furan ring hydrogenation. • The formation of Brønsted acid centers catalyzed the etherification step. • A Pd-Brønsted-Lewis acid synergistic catalysis mechanism was proposed. Production of ethers from biomass-derived platform compounds is a substantial scientific challenge and industrial pursuit. In this study, an effective bifunctional Pd/SiO 2 -Al 2 O 3 -30 catalyst was synthesized for the selective hydrogenation-etherification of furfural (FAL) to furfuryl ether and exhibited an 86.2% 2-(isopropoxymethyl)furan yield with the synergistic catalysis of Pd particles and Brønsted–Lewis acid sites. The incorporation of Si with Al 2 O 3 in the catalysts weakened the metal-support interaction and resulted in larger Pd particles, which inhibited the hydrogenation of the furan ring. Meanwhile, the formation of Brønsted acid centers catalyzed the etherification step and promoted the selectivity to corresponding ethers. Furthermore, extensive reaction results and characterizations uncovered the metal-acid synergistic catalysis mechanism for the selective hydrogenation-etherification of FAL. This work provides an innovative strategy for preparing effective metal-acid bifunctional catalysts for the hydrogenation-etherification of bio-aldehydes to ethers. [ABSTRACT FROM AUTHOR]

This article discusses the development of a Brønsted acid catalyzed asymmetric silylation method for biaryl diols, which allows for the synthesis of axially chiral biaryl silyl ethers. The researchers tested different catalysts and reaction conditions to optimize the enantioselectivity of the silylation reaction. They also conducted control experiments to confirm that the reaction proceeds through a desymmetrization-kinetic resolution sequence. The authors acknowledge the contribution of Professor Martin Oestreich, who independently investigated the same transformation. [Extracted from the article]

We report a Brønsted acid‐catalyzed synthesis of tetrasubstituted allenyl compounds decorated with heterocyclic sulfenyl group. The reaction proceeds readily from available propargylic alcohols in the presence of pentacarboxycyclopenatadienes (PCCPs) as organocatalysts. The developed strategy provides tetrasubstituted allene derivatives in high yields (from 55 to 98 %) and under mild reaction conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Glycerol C-O cleavage via protonation dehydration mechanism at reaction condition. • Brønsted acid generated in-situ by H spill over from Pt to WO x across Pt-WO x interface. • Primary/secondary C-O cleavage: linear/non-monotonic relation with NH 3 binding. • Brønsted acid strength is a descriptor for catalyst activity and selectivity. • Increasing strong Brønsted acid sites likely to enhance 1,3-PDO yield. DFT simulations predicted the C-O bond cleavage in glycerol on Brønsted acidic Pt-WO x catalyst under a hydrogen atmosphere to be via a "protonation dehydration" mechanism. Interfacial Pt-WO x sites facilitate Brønsted acid (BA) site formation by hydrogen spillover and synergistic activity of Pt and WO x. At strong BA sites, selective formation of 1,3-PDO is likely due to the large difference of over 40 kJ/mol in primary and secondary C-O bond cleavage barriers. The secondary C-O bond cleavage has a linear relation with NH 3 binding energy while there is a non-monotonic trend for the primary C-O cleavage. Hence, Brønsted acid strength is a potential descriptor for the catalyst activity and 1,3-PDO selectivity. Synthetic strategies enabling fine dispersion of WO x to trimeric units on the Pt nanoparticles, while preventing W doping and agglomeration of WO x to 3D WO 3 on small Pt nanoparticles are desirable for high BA strength and thereby 1,3-PDO yield. [ABSTRACT FROM AUTHOR]

Over the last ten years, the combination of organocatalysis with transition metal (TM) catalysis has become one of the most important toolboxes used for synthesizing optically pure compounds containing chiral quaternary centers, including spiro heterocyclic molecules. The dominant method in the enantioselective synthesis of spiro heterocyclic compounds based on synergistic catalysis includes chiral aminocatalysis and NHC catalysis, as already established covalent organocatalytic strategies. Another area of organocatalysis widely combined with TM catalysis producing enantiomerically enriched spiro heterocyclic compounds is non‐covalent catalysis, dominated by chiral phosphoric acids, thiourea, and squaramide derivatives. This review article aims to summarize enantioselective methods used for constructing spirocyclic heterocycles based on a combination of organocatalysis and transition metal catalysis. [ABSTRACT FROM AUTHOR]

WOx/ZrO2 catalysts with different tungsten loadings were prepared via wet impregnation, wherein the presence of WO3 appreciably altered the textural and structural properties. According to Raman spectroscopy, loadings as high as 15 wt% WO3 marked the onset of WO3-nanoparticle formation. Moreover, NH3-TPD and DRIFT spectroscopy with pyridine adsorption revealed that 15 wt% WO3/ZrO2 showed the highest total number of acid centres together with the largest population of Brønsted acid sites. This material was able to achieve full conversion of α-angelica lactone in n-butanol leading to the production of 43% n-butyl levulinate and 53% pseudo-butyl levulinate after 5 h at 75 °C. The catalytic performance and selectivity towards the esters were found to be strongly related to the concentration of Lewis and Brønsted acid species. [ABSTRACT FROM AUTHOR]

This article describes the development of a metal and additive‐free protocol that utilizes acetic acid (AcOH) as a catalyst for the C3‐alkylation of indolizines using para‐Quinone Methides (p‐QMs) as an alkylation agent. The metal and additive free method offers an easy route to various substituted indolizine derivatives with good functional group tolerance and delivering acceptable good yields (up to 93%). A gram‐scale synthesis and further product derivatization show the synthetic potential of this technique. The significance of these findings for medicinal chemistry makes this easy and green approach relevant to both medicinal and synthetic organic chemists, given the crucial role of indolizine in the pharmaceutical industry. [ABSTRACT FROM AUTHOR]

The effect of phosphoric acid treatment on the physical-chemical properties and catalytic activity of the niobium-doped silica-titania bifunctional catalyst was investigated. As part of the synthesis procedure to produce xPO4−/Nb/TiO2-SiO2, different concentrations of phosphoric acid (H3PO4) were used (x= 0, 0.05, 0.10, 0.15, 0.20, 0.25 M). As shown by XRD analysis, the samples synthesized using 0–0.20 M H3PO4 were in amorphous form, as featureless diffractograms were obtained, indicating the PO4− groups were dispersed homogeneously on the surface of Nb doped SiO2-TiO2. Due to the increased concentration of acid, other compounds were formed in the samples by reactions between PO4− and Nb and/or Ti. Additionally, UV-Vis DRS results indicated that the presence of the PO4− group accelerated the transformation of hydrated tetrahedral Ti species into isolated tetrahedral Ti species. An experimental investigation of the catalytic performance of the catalyst was conducted using 1,2-epoxyoctane as an oxidant for the epoxidation of 1-octene to 1,2-octanediol. It has been demonstrated that H3PO4 treatment was essential for oxidative and acidity active site formation. The current research findings strongly suggested that Nb-doped TiO2-SiO2 treated with 0.2 M H3PO4 was the most effective bifunctional catalyst in generating 1,2-octanediol.

A Brønsted acid‐catalyzed, transition metal‐free intramolecular 7‐endo hydroarylation reaction of 1,5‐diaryl‐1‐pentynes has been developed. The use of 1,1,1,3,3,3‐hexafluoro‐2‐propanol (HFIP) as a solvent was found to be critical for this process. Using the present methodology, we have accomplished the synthesis of KGP‐18, an analogue of the anticancer natural product combretastatin A4. [ABSTRACT FROM AUTHOR]

A Brønsted acid‐catalysed cyclization of ene‐ynamides has been developed to construct 7‐ or 8‐membered azacycles in good to high yields. The use of a simple C=C double bond as a nucleophile enables the synthesis of medium‐sized ring from an acyclic ynamide. This reaction system features simple and mild reaction conditions without any metal catalysts, and no requirement of high dilution for medium‐sized ring formation. This method is applicable to a variety of substituents on the ynamides, such as alkyl, aryl, acetylene and silyloxy group. [ABSTRACT FROM AUTHOR]

This review is devoted to underpinning the contributions of Indian researchers towards asymmetric organocatalysis. More specifically, a comprehensive compilation of reactions mediated by a wide range of non-covalent catalysis is illustrated. A detailed overview of vividly catalogued asymmetric organic transformations promoted by hydrogen bonding and Brønsted acid catalysis, alongside an assortment of catalysts is provided. Although asymmetric organocatalysis has etched itself in history, we aim to showcase the scientific metamorphosis of Indian research from baby steps to large strides within this field. 1 Introduction 2 Non-Covalent Catalysis and Its Various Activation Modes 3 Hydrogen-Bonding Catalysis 3.1 Urea- and Thiourea-Derived Organocatalysts 3.1.1 Thiourea-Derived Organocatalysts 3.1.2 Urea-Derived Organocatalysts 3.2 Squaramide-Derived Organocatalysts 3.2.1 Michael Reactions 3.2.2 C-Alkylation Reactions 3.2.3 Mannich Reactions 3.2.4 [3+2] Cycloaddition Reactions 3.3 Cinchona-Alkaloid-Derived Organocatalysts 3.3.1 Michael Reactions 3.3.2 Aldol Reactions 3.3.3 Friedel–Crafts Reactions 3.3.4 Vinylogous Alkylation of 4-Methylcoumarins 3.3.5 C-Sulfenylation Reactions 3.3.6 Peroxyhemiacetalisation of Isochromans 3.3.7 Diels–Alder Reactions 3.3.8 Cycloaddition Reactions 3.3.9 Morita–Baylis–Hilman Reactions 4 Brønsted Acid Derived Organocatalysts 4.1 Chiral Phosphoric Acid Catalysis 4.1.1 Diels–Alder Reactions 4.1.2 Addition of Ketimines 4.1.3 Annulation of Acyclic Enecarbamates 5 Conclusion [ABSTRACT FROM AUTHOR]

A simple protocol catalyzed by a Brønsted acid, trifluoromethanesulfonic acid (CF3 SO3 H), to synthesize conjugated diene-diones from easily accessible tertiary propargyl alcohols and 1,3-dicarbonyl compounds is described. Reactions are performed in an air atmosphere by using undried solvents with water being the environmentally benign side product of the process. Preliminary synthetic applications of the conjugated diene-diones in the formation of conjugated dieneones and furans are also reported herein. [ABSTRACT FROM AUTHOR]

AlCl3-mediated protodeboronation of arylboronic acids and esters is reported herein. This method features mild reaction conditions, high reaction yields, as well as short reaction times. Mechanistic studies based on 11B NMR spectroscopy suggest that it might proceed through initial boron activation by coordination of AlCl3 to the oxygen atom of arylboronic acid or ester groups. AlCl3-mediated protodeborylation of arylboronic acids and esters was reported with mild reaction conditions, high reaction yields as well as a simple work-up procedure. [ABSTRACT FROM AUTHOR]

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A Brønsted acid mediated annulation of cyclic α‐hydroxy amides with cycloalkanones provide access to unusual double spirocyclic oxazolidin‐4‐one derivatives. This spirocyclization occurs in one‐pot and the overall process is highly efficient. The annulation reaction does not need metal‐catalyst. No self‐condensation of cycloalkanone occurs under acidic conditions. The synthetic technique is operationally simple and chemoselective. The transformation exhibits broad scope constructing a large array of highly functionalized complex double spirocyclic oxazolidin‐4‐one derivatives in good yields. Notably, all the reactions have been carried out in gram scale. [ABSTRACT FROM AUTHOR]

A study on relative catalytic efficacy of 1,3-diaryl thioureas has revealed that 1-[3,5-bis(trifluoromethyl)phenyl]-3-phenylthiourea is an efficient alternative to the Schreiner's thiourea catalyst (STC) for acid-catalyzed activation of carbonyl compounds in the synthesis of symmetrical trisubstituted methanes (TRSMs) at an elevated temperature. Since the preparation of STC involves the use of toxic thiophosgene, the 1-[3,5-bis(trifluoromethyl)phenyl]-3-phenylthiourea represents an easily accessible and simpler alternative. Strikingly, the temperature-assisted reaction showed significantly shorter reaction time in comparison to photoirradiation in the thiourea-catalyzed Friedel–Crafts type reaction of indole with aldehydes. Simple reaction set-up and excellent yields are some of the highlights of the reported method. [ABSTRACT FROM AUTHOR]

An enantioselective aza-Piancatelli rearrangement has been developed using a chiral Brønsted acid based on pentacarboxycyclopentadiene (PCCP). This reaction provides rapid access to valuable chiral 4-amino-2-cyclopentenone building blocks from readily available starting material and is operationally simple.

Selective hydrogenolysis of biomass‐derived glycerol to propanediol is important for producing high value‐added chemicals from renewable resources but faces a huge challenge. Here we report a transition metal doped Pt/TiO2 catalyst with incorporated Cr, Mo, or W oxides, which exhibits the selective formation of 1,2‐propanediol or 1,3‐propanediol with a yield from 51.2% to 82.5% toward glycerol hydrogenolysis. In situ experimental studies verify that the surrounding CrOx decreases the hydrogenating ability of Pt, leading to the formation of 1,2‐propanediol, while the MoOx or WOx brings the Brønsted acid, giving 1,3‐propanediol. This modification based on the catalyst compositions alters the reaction pathway with a different adsorption and bond scission mechanism, which can be extended to other sustainable catalytic systems. [ABSTRACT FROM AUTHOR]

Selective hydrogenolysis of biomass‐derived glycerol to propanediol is important for producing high value‐added chemicals from renewable resources but faces a huge challenge. Here we report a transition metal doped Pt/TiO2 catalyst with incorporated Cr, Mo, or W oxides, which exhibits the selective formation of 1,2‐propanediol or 1,3‐propanediol with a yield from 51.2% to 82.5% toward glycerol hydrogenolysis. In situ experimental studies verify that the surrounding CrOx decreases the hydrogenating ability of Pt, leading to the formation of 1,2‐propanediol, while the MoOx or WOx brings the Brønsted acid, giving 1,3‐propanediol. This modification based on the catalyst compositions alters the reaction pathway with a different adsorption and bond scission mechanism, which can be extended to other sustainable catalytic systems. [ABSTRACT FROM AUTHOR]

Cellulose is the primary substance of sugarcane bagasse and is essential for producing chemicals such as levoglucosan (LG), which can be synthesized through various methods, such as cellulose hydrolysis catalyzed by a Brønsted acid. This recent research was preceded by a preliminary study on glucose hydrolysis into LG with hydrochloric acid (HCl) as the catalyst. Following the preliminary one, the main study was conducted in two stages: alkaline-acid pre-treatment to separate cellulose from other undesired components in bagasse and cellulose hydrolysis in generating LG. The cellulose hydrolysis was catalyzed by HCl at temperatures ranging from 140 to 180 °C with catalyst concentrations ranging from 0.1 to 0.5 M and solid-to-liquid ratios ranging from 1 to 10%. The experimental results showed that LG could be synthesized from glucose and cellulose, and all the variables observed, namely temperature, catalyst concentration, and solid-to-liquid ratio, influenced the formation of LG. The LG formed was very unstable, thus easily be degraded into other compounds. The cellulose hydrolysis to LG occurred through the following route: cellulose-glucose-LG-decomposition compounds. The reaction's controlling step was the cellulose conversion into glucose for its lowest reaction rate constant compared to the others. [ABSTRACT FROM AUTHOR]

Chiral imidodiphosphates (IDPs) have emerged as strong Brønsted acid catalysts for many enantioselective processes. However, the dynamic transformation between O,O‐syn and O,O‐anti conformers typically results in low enantioselectivity. Here we demonstrate that topologies of metal‐organic frameworks (MOFs) can be exploited to control IDP conformations and local chiral microenvironments for enantioselective catalysis. Two porous Dy‐MOFs with different topologies are obtained from an enantiopure 1,1′‐biphenol IDP‐based tetracarboxylate ligand. While the ligand adopts a 4‐ or 3‐connected (c) binding mode, all IDPs are rigidified to get only a single O,O‐syn conformation and display greatly enhanced Brønsted acidity relative to the free IDP. The MOF with the 4‐c IDP that has a relatively less compact shape than the 3‐c IDP can be an efficient and recyclable heterogeneous Brønsted acid catalysing the challenging asymmetric O,O‐acetalization reaction with up to 96 % enantiomeric excess. [ABSTRACT FROM AUTHOR]

Since the innovative work of Terada and Akiyama, asymmetric reaction using chiral Brønsted acid has attracted great attention. Asymmetric aldol reactions are extensively studied in different organocatalysis. Brønsted acid-catalyzed aldol reaction may be carried out directly without modification of the substrates or Mukaiyama type aldol reaction using silyl enol ether as nucleophiles. The reaction may proceed through the formation of enol intermediate followed by the attack to the electrophile while Mukaiyama type aldol reactions may follow two mechanistic pathways-Brønsted acidic pathways where Brønsted acid directly activates the substrate or Lewis acid pathways where Brønsted acid acts as precatalyst. Here, the recent advancement of asymmetric aldol reactions using chiral Brønsted acid as a catalyst and the fate of the catalysts in the reaction has been discussed in this review. It is observed that some kinds of aldol reactions have rarely been studied and need more attention. [ABSTRACT FROM AUTHOR]

Baeyer–Villiger oxidation can synthesize a series of esters or lactones that have essential application value but are difficult to be synthesized by other methods. Cycloketones can be oxidized to lactones using molecular oxygen, peroxy acids, or hydrogen peroxide as an oxidant. Hydrogen peroxide is one of the environmental oxidants. Because of the weak oxidation ability of hydrogen peroxide, Bronsted acids and Lewis acids are used as catalysts to activate hydrogen peroxide or the carbonyl of ketones to increase the nucleophilic performance of hydrogen peroxide. The catalytic mechanisms of Bronsted acids and Lewis acids differ in the Baeyer–Villiger oxidation of cyclohexanone with an aqueous solution of hydrogen peroxide as an oxidant. [ABSTRACT FROM AUTHOR]

This review focuses on the carbocyclization reactions of alkyne-containing substrates catalyzed by Brønsted acids. The electrophilic activation occurs either by direct protonation of the alkyne or by formation of an intermediate cation that further reacts with the alkyne to give a key vinyl cation intermediate. Specific focus is placed on the selectivity of the various methodologies described herein and on mechanistic rationales. 1 Introduction 2 Brønsted Acid Catalyzed Alkyne Carbocyclization Involving C(sp) Reaction Partners 2.1 Brønsted Acid Catalyzed Cyclization of Diynes 2.2 Brønsted Acid Catalyzed Cyclization of Allenynes 3 Brønsted Acid Catalyzed Alkyne Carbocyclization Involving C(sp2) Reaction Partners 3.1 Brønsted Acid Catalyzed Cycloisomerization of Enynes 3.1.1 Initial Protonation of the Alkene Function 3.1.2 Initial Protonation of the Alkyne Function 3.1.3 A Conia-Ene Reaction 3.2 Electrophile-Induced Carbocyclization Involving Other C(sp2)-Based Reaction Partners 3.2.1 Iminium Electrophiles 3.2.2 Oxonium Electrophiles 3.2.3 Isocyanate and Thioisocyanate Electrophiles 3.3 Brønsted Acid Catalyzed Cycloisomerization of Aryl-alkynes 3.3.1 Reactions Using Excess or Stoichiometric Amounts of Brønsted Acid 3.3.2 Reactions Using Substoichiometric Amounts of Brønsted Acid 3.3.3 Heteroatom-Substituted Alkynes 3.3.4 Enantioselective Brønsted Acid Catalyzed Cycloisomerization of Aryl-alkynes 4 Brønsted Acid Catalyzed Alkyne Carbocyclization Involving C(sp3) Reaction Partners: Alkyne-alkane Cycloisomerization 5 Conclusion and Outlook [ABSTRACT FROM AUTHOR]