MIL‐101‐SO3H: A Highly Efficient Brønsted Acid Catalyst for Heterogeneous Alcoholysis of Epoxides under Ambient Conditions

For the first time, a ～100 % sulfonic acid functionalized metal–organic framework (MOF), MIL‐101‐SO₃H, with giant pores has been prepared by a hydrothermal process followed by a facile postsynthetic HCl treatment strategy. The replete readily accessible Lewis acidic and especially Brønsted acidic sites distributed throughout the framework as well as high stability endow the resultant MOF exceptionally high efficiency and recyclability, which surpass all other MOF‐based catalysts, for the ring opening of epoxides with alcohols (especially, methanol) as nucleophiles under ambient conditions.     

Terbium–organic framework as heterogeneous Lewis acid catalyst for β‐aminoalcohol synthesis: Efficient,reusable and green catalytic method

A terbium–organic framework (Tb‐MOF) was prepared using a previously reported procedure. Tb‐MOF was characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, powder X‐ray diffraction and surface area analysis. Tb‐MOF was employed as a heterogeneous Lewis acid catalyst for the synthesis of β‐aminoalcohols. Also, the effect of ultrasonic irradiation was examined in the catalytic aminolysis of styrene oxide. The reaction conditions were optimized by variation of reaction time, catalyst concentration and solvent. A variety of β‐aminoalcohols were synthesized and characterized. The Tb‐MOF catalyst showed excellent selectivity and high yield for these transformations.     

A 4‐Hydroxypyrrolidine‐Catalyzed Mannich Reaction of Aldehydes: Control of anti‐Selectivity by Hydrogen Bonding Assisted by Brønsted Acids

An anti‐selective Mannich reaction of aldehydes with N‐sulfonyl imines has been developed by using a 4‐hydroxypyrrolidine in combination with an external Brønsted acid. The catalyst design is based on three elements: the α‐substituent of the pyrrolidine, the 4‐hydroxy group, and the Brønsted acid, the combination of which is essential for high chemical and stereochemical efficiency. The reaction works with aromatic aldehyde‐derived imines, which have rarely been employed in previously reported enamine‐based anti‐Mannich reactions. Additionally, both N‐tosyl and N‐nosyl imines can be successfully used and the Mannich adducts can be easily reduced or oxidized, and after N‐deprotection the corresponding β‐amino acids and β‐amino alcohols can be obtained with good yields. The results also show that this ternary catalytic system may be practical in other enamine‐based reactions.     

Phosphonate‐Modified UiO‐66 Brønsted Acid Catalyst and Its Use in Dehydra‐Decyclization of 2‐Methyltetrahydrofuran to Pentadienes

Phosphorus‐modified all‐silica zeolites exhibit activity and selectivity in certain Brønsted acid catalyzed reactions for biomass conversion. In an effort to achieve similar performance with catalysts having well‐defined sites, we report the incorporation of Brønsted acidity to metal–organic frameworks with the UiO‐66 topology, achieved by attaching phosphonic acid to the 1,4‐benzenedicarboxylate ligand and using it to form UiO‐66‐PO₃H₂ by post‐synthesis modification. Characterization reveals that UiO‐66‐PO₃H₂ retains stability similar to UiO‐66, and exhibits weak Brønsted acidity, as demonstrated by titrations, alcohol dehydration, and dehydra‐decyclization of 2‐methyltetrahydrofuran (2‐MTHF). For the later reaction, the reported catalyst exhibits site‐time yields and selectivity approaching that of phosphoric acid on all‐silica zeolites. Using solid‐state NMR and deprotonation energy calculations, the chemical environments of P and the corresponding acidities are determined.     

Highly efficient and green approach for the synthesis of spirooxindole derivatives in the presence of novel Brønsted acidic ionic liquids incorporated in UiO‐66 nanocages

An efficient and green approach is reported for the rapid synthesis of spirocyclic 2‐oxindole using triethylenediamine or imidazole Brønsted acidic ionic liquids supported in Zr metal–organic framework (TEDA/IMIZ‐BAIL@UiO‐66) as a novel, superior and retrievable heterogeneous catalyst under ultrasonic irradiation. Heterocyclic compounds including pyrido[2,3‐d:6,5‐d′]dipyrimidines and indeno[2′,1′:5,6]pyrido[2,3‐d]pyrimidines were obtained by the one‐pot condensation reaction of 6‐amino‐1,3‐dimethyluracil, isatins and cyclic 1,3‐diketone (barbituric acid or 1,3‐indanedione). The reusability of the catalyst, low catalyst loading, short reaction times, excellent yields, simple work‐up, and use of sonochemical procedure as a mild process and an alternative energy source are some of the advantages of this method. Furthermore, the novel heterogeneous nanocomposite was fully characterized using various techniques.     

Synthesis of chromene derivatives in the presence of mordenite zeolite/MIL‐101 (Cr) metal–organic framework composite as catalyst

In the present study, the synthesis of mordenite zeolite/MIL‐101(Cr) metal–organic framework (MOF) composite [MOR/MIL‐101(Cr)] using the ship in a bottle method was suggested. The properties of prepared composite and individual MOF and MOR zeolite were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), nitrogen adsorption–desorption measurement, and thermogravimetric analysis (TGA). The XRD results indicated diffraction peaks for each compound (MOR and MOF) in composite. The SEM and TEM images showed the formation of plates MOR (with size of 2.5 × 3 μm) along with spherical particles MIL‐101. The Brunauer–Emmett–Teller results showed that the surface area of the composite was smaller than individual MOF and MOR zeolite. Based on TGA plots, the hybrid zeolite/MOF composite was more thermally stable compared with the isolated MIL‐101(Cr). The composite was functionalized by post‐synthetic modification to obtain acid–base bifunctionality (H‐MOR/MIL‐101‐ED) for the synthesis of chromene derivatives. The acidity from framework Al‐O(H)‐Si sites in MOR and basicity from amine groups in MIL‐101 were obtained by post‐synthetic modification.     

Immobilization of phosphotungstic acid in an amino‐containing metal–organic framework for oxidative desulfurization

A composite material has been successfully synthesized using an amino‐containing metal–organic framework (NH₂‐MOF) and phosphotungstic acid (PTA). This composite was characterized using X‐ray diffraction, high‐resolution transmission electron microscopy, nitrogen adsorption–desorption measurements, Fourier transform infrared spectroscopy and X‐ray fluorescence. Characterization results confirmed the immobilization and good distribution of PTA in the NH₂‐MOF. The PTA/NH₂‐MOF was subsequently applied in the oxidative desulfurization of dibenzothiophene (DBT) with H₂O₂ as the oxidant in n‐octane under atmospheric conditions. Under optimal reaction conditions, the oxidative desulfurization conversion of DBT reached 100%, and there was no significant decrease of the catalytic activity after four recycles. Kinetic experiments were also performed for the reaction at various temperatures, which indicated that oxidative reaction rates followed pseudo first‐order kinetics, and the apparent activation energy for the desulfurization reaction was 34.1 kJ mol^?1. The results indicated that this material exhibited excellent catalytic performance for oxidative desulfurization of DBT. Copyright © 2016 John Wiley & Sons, Ltd.     

Brønsted Acid‐Catalyzed Cascade Reactions Involving 1,2‐Indole Migration

A cascade reaction of indoles with propargylic diols involving an unprecedented metal‐free 1,2‐indole migration onto an alkyne was carried out. DFT calculations support a mechanism consisting of a concerted nucleophilic attack of the indole nucleus with loss of water, followed by the 1,2‐migration and subsequent Nazarov cyclization. This Brønsted acid‐catalyzed protocol affords indole‐functionalized benzofulvene derivatives in high yields.     

Asymmetric Friedel–Crafts Reaction of 4,7‐Dihydroindoles with Nitroolefins by Chiral Brønsted Acids under Low Catalyst Loading

Slowly does it! By adding the substrate by a syringe pump, a highly efficient Friedel–Crafts reaction of 4,7‐dihydroindoles with nitroolefins was realized with 0.5 mol % of a chiral phosphoric acid. The Friedel–Crafts alkylation, together with a subsequent oxidation of the product, led to 2‐substituted indoles in excellent enantiomeric excesses, which can be easily transformed to enantioenriched tetrahydro‐γ‐carbolines.

     

Salicylato Titanocene Complexes as Cooperative Organometallic Lewis Acid and Brønsted Acid Catalysts for Three‐Component Mannich Reactions

A binary acid system has been developed that features an air‐stable organometallic precursor, titanocene dichloride, and simple organic cooperative Brønsted acids, which allowed for mild and highly efficient Mannich reactions of both aryl and alkyl ketones with excellent yields and satisfactory diastereoselectivity. Mechanistic studies, including ¹H NMR titration, X‐ray structure analyses as well as isolation of catalytically active species, elucidated the dramatic synergistic effects of this new binary acid system.     

Efficient and recyclable novel Ni‐based metal–organic framework nanostructure as catalyst for the cascade reaction of alcohol oxidation–Knoevenagel condensation

A novel Ni‐based metal–organic framework (Ni‐MOF) with a Schiff base ligand as an organic linker, Ni₃(bdda)₂(OAc)₂?6H₂O (H₂bdda = 4,4′‐[benzene‐1,4‐diylbis(methylylidenenitrilo)]dibenzoic acid), was synthesized and characterized using powder X‐ray powder diffraction, thermogravimetric analysis, Brunauer–Emmett–Teller measurements, inductively coupled plasma atomic emission spectroscopy, transmission electron microscopy, elemental analysis and Fourier transform infrared spectroscopy. The synthesized Ni‐MOF exhibited a high catalytic activity in benzyl alcohol oxidation using tert‐butyl hydroperoxide under solvent‐free conditions. Also, the efficiency of the catalyst was investigated in the cascade reaction of oxidation–Knoevanagel condensation under mild conditions. The Ni‐MOF catalyst could be recovered and reused four times without significant reduction in its catalytic activity.     

Bifunctional Brønsted Base Catalyzes Direct Asymmetric Aldol Reaction of α‐Keto Amides

The first enantioselective direct cross‐aldol reaction of α‐keto amides with aldehydes, mediated by a bifunctional ureidopeptide‐based Brønsted base catalyst, is described. The appropriate combination of a tertiary amine base and an aminal, and urea hydrogen‐bond donor groups in the catalyst structure promoted the exclusive generation of the α‐keto amide enolate which reacted with either non‐enolizable or enolizable aldehydes to produce highly enantioenriched polyoxygenated aldol adducts without side‐products resulting from dehydration, α‐keto amide self‐condensation, aldehyde enolization, and isotetronic acid formation.     

Deep desulfurization by oxidation using an active ionic liquid‐supported Zr metal–organic framework as catalyst

In this study, a Zr metal–organic framework (UIO‐66) was synthesized with zirconium tetrachloride and terephthalic acid using the solvent method. Then various masses of 1‐methylimidazolium‐3‐propylsulfonate hydrosulfate (PSMIMHSO₄) were supported on the UIO‐66 as catalysts, which were used for catalytic oxidative desulfurization. Sulfur removal using 400 mg of 40% PSMIMHSO₄ supported on the UIO‐66 of greater than 94% was obtained at 313 K for 20 min with an O/S molar ratio of 7:1. The results obtained in this work could provide useful information for the design of water‐stable metal–organic frameworks with permanent porosity in applications of catalytic oxidative desulfurization. Copyright © 2014 John Wiley & Sons, Ltd.     

A Gold‐ and Brønsted Acid Catalytic Interplay Towards the Synthesis of Highly Substituted Tetrahydrocarbazoles

The reaction of indoles and stabilized cyclopropyl alkynes under gold‐ and/or gold & Brønsted acid‐catalysis provided access to highly substituted tetrahydrocarbazoles. A mechanistic study revealed the complex mechanism underlying these processes and the opportunistic cooperation of Lewis and Brønsted acid‐catalysts towards the formation of complex molecular scaffolds.     

Nano palladium supported on high‐surface‐area metal–organic framework MIL‐101: an efficient catalyst for Sonogashira coupling of aryl and heteroaryl bromides with alkynes

Palladium nanoparticle‐incorporated metal–organic framework MIL‐101 (Pd/MIL‐101) was successfully synthesized and characterized using X‐ray diffraction, nitrogen physisorption, X‐ray photoelectron, UV–visible and infrared spectroscopies, and transmission electron microscopy. The characterization techniques confirmed high porosity and high surface area of MIL‐101 and high stability of nano‐size palladium particles. Pd/MIL‐101 nanocomposite was investigated for the Sonogashira cross‐coupling reaction of aryl and heteroaryl bromides with various alkynes under copper‐free conditions. The reusability of the catalyst was tested for up to four cycles without any significant loss in catalytic activity. Copyright © 2015 John Wiley & Sons, Ltd.     

Direct α‐Alkylation of Aldehydes by Brønsted‐Acid Catalysis

A Brønsted acid catalyzed direct alkylation reaction of aldehydes was described. The 3,5‐dinitrobenzoic acid promoted the reaction between aldehydes and diarylmethanols to afford the corresponding alkylation products with middle to high yields (up to 91% yield).     

Brønsted Acid Catalyzed Friedel–Crafts‐Type Coupling and Dedinitrogenation Reactions of Vinyldiazo Compounds

The direct Friedel–Crafts‐type coupling and dedinitrogenation reactions of vinyldiazo compounds with aromatic compounds using a metal‐free strategy are described. This Brønsted acid catalyzed method is efficient for the formation of α‐diazo β‐carbocations (vinyldiazonium ions), vinyl carbocations, and allylic or homoallylic carbocation species via vinyldiazo compounds. By choosing suitable nucleophilic reagents to selectively capture these intermediates, both trisubstituted α,β‐unsaturated esters, β‐indole‐substituted diazo esters, and dienes are obtained with good to high yields and selectivity. Experimental insights implicate a reaction mechanism involving the selective protonation of vinyldiazo compounds and the subsequent release of dinitrogen to form vinyl cations that undergo intramolecular 1,3‐ and 1,4‐ hydride transfer processes as well as fragmentation.