Novel synthesis of alkoxy substituted oxa[9]helicenes by the reaction of helical quinone with alcohols

The reaction of helical quinone with alcohols in the presence of Brønsted acid such as para-toluenesulfonic acid (pTSA) or HCl proceeded smoothly to produce the corresponding alkoxy substituted oxa[9]helicenes in good yields.     

Direct sulfonylation of Baylis-Hillman alcohols and diarylmethanols with TosMIC in ionic liquid-[Hmim]HSO4: an unexpected reaction

A Brønsted acidic ionic liquid-[Hmim]HSO₄ promoted unexpected reaction of Baylis-Hillman alcohols and diarylmethanols with p-toluenesulfonylmethyl isocyanide (TosMIC) affording the corresponding sulfone derivatives instead of N-tosylmethyl amides is reported. After isolation of the product, the ionic liquid [Hmim]HSO₄ was easily recycled for further use.     

应用原位漫反射红外-质谱技术研究CuO/Al2O3催化剂表面酸性及其反应性能

应用原位漫反射红外-质谱联用、程序升温和暂态响应技术研究了CuO/Al₂O₃催化剂表面酸性及其反应性能. 实验结果表明, CuO/Al₂O₃催化剂表面呈Lewis酸性, 硫化不仅可增强CuO/Al₂O₃催化剂的Lewis酸性, 而且可产生新的Brønsted酸性位; 吸附于Lewis酸性位的NH₃具有选择性催化还原(SCR)活性. 而在硫化样Cu8(400S)中Lewis和Brønsted酸性位同时存在的情况下, 吸附于Lewis和Brønsted酸性位的氨均具有SCR活性, 且后者较前者弱; CuO/Al₂O₃催化剂上的SCR反应遵循Eley-Rideal机理, 即SCR反应发生于吸附态NH₃与气相NO之间.     

An efficient and chemoselective Brønsted acidic ionic liquid-catalyzed N-Boc protection of amines

The first report of a Brønsted acidic ionic liquid, 1-methylimidazolium tetrafluoroborate [(HMIm)BF₄], catalyzed efficient and chemoselective N-Boc protection of various amines using (Boc)₂O is presented. Optically pure amino alcohols and amino acid esters were converted efficiently to their corresponding optically pure N-Boc derivatives. The reported method is mild, solvent-free and has the advantages of both homogeneous and heterogeneous catalysis with high product yields, selectivity and ease of product separation.     

Brønsted acid TfOH-mediated reactions of 2-(arylmethylene)cyclopropylcarbinols with acetonitrile

We report herein Brønsted acid TfOH-mediated reactions of 2-(arylmethylene)cyclopropylcarbinols with acetonitrile to give the corresponding ring-enlarged N-(3-arylmethylidenecyclobutyl)acetamides in moderate to good yields under mild conditions. A plausible mechanism is proposed on the basis of previous investigations.     

Brønsted acidic magnetic nano-Fe3O4-adorned calix[n]arene sulfonic acids: synthesis and application in the nucleophilic substitution of alcohols

Three magnetically recoverable Brønsted acidic calix[n]arene derivatives were successfully constructed by immobilizing calix[n]arene sulfonic acids onto silica-coated magnetic nanoparticles, a process, which allows calix[n]arene derivatives to acquire magnetic properties. All of the magnetically recoverable Brønsted acidic calix[n]arenes efficiently catalyze the coupling of electron-rich arenes with some alcohols in water. After separation and recovery from the reaction mixture by a simple magnet, these Brønsted acidic calix[n]arenes can be recycled many times without losing their catalytic activity.     

Solvent-free Brønsted acid catalysed alkylation of arenes and heteroarenes with benzylic alcohols

A simple and efficient alkylation of aromatic and heteroaromatic compounds via the direct S_N1-type nucleophilic substitution of benzylic alcohols in the presence of catalytic amounts of the strong Brønsted acid o-benzenedisulfonimide under neat conditions is herein reported. A library of di- and triaryl (and heteroaryl) methanes was prepared in good yields and high regioselectivity. The observed reactivity was shown to be in agreement with Mayr's nucleophilicity and electrophilicity scales.     

Vanadium-catalyzed oxidative bromination promoted by Brønsted acid or Lewis acid

The oxidative bromination of arenes was induced by a vanadium catalyst in the presence of a bromide salt and a Brønsted acid or a Lewis acid under molecular oxygen, which provides an eco-friendly bromination method as compared with a conventional bromination one with bromine. This catalytic reaction could be applied to the bromination of alkenes and alkynes to give the corresponding vic-bromides. Use of aluminum halide as a Lewis acid in place of a Brønsted acid was demonstrated to provide a more practical protocol for the oxidative bromination. From ketones, α-bromination products were obtained. AlBr₃ was found to serve as both a bromide source and a Lewis acid to induce the bromination smoothly. ⁵¹V NMR experiment showed that this catalytic bromination is likely to depend on the redox cycle of a vanadium catalyst under molecular oxygen.     

Novel Brønsted acidic deep eutectic solvent as reaction media for esterification of carboxylic acid with alcohols

New halogen-free Brønsted acidic deep eutectic solvents (DES) have been prepared by mixing new quaternary ammonium methanesulfonate salts with p-toluenesulfonic acid (PTSA). They have been used as dual solvent-catalyst for esterification of several carboxylic acids with different alcohols with a reagent molar ratio of 1:1. The method is mild, safe, and simple. Ease of recovery and reusability of DES with high activity makes this method efficient and eco-friendly. The tunability of DES properties, attained by changes in the cation, was performed in order to achieve various esters in good yields.     

C3-Symmetric chiral trisimidazoline: the role of a third imidazoline and its application to the nitro Michael reaction and the α-amination of β-ketoesters

We describe the necessity of the C₃-symmetry and the role of a third imidazoline of trisimidazoline 3, which was recently developed by us as a new entry of organocatalyst. The utility of 3 as a Brønsted base catalyst in the nitro Michael reaction and the α-amination of β-ketoesters was shown, and the recyclability of the catalyst was also demonstrated.     

o-Benzenedisulfonimide as a reusable Brønsted acid catalyst for an efficient and facile synthesis of quinolines via Friedländer annulation

The synthesis of quinolines via Friedländer annulation was carried out in the presence of catalytic amount of o-benzenedisulfonimide as Brønsted acid organocatalyst; the reaction conditions were mild and the yields of the target products were good. The organocatalyst was easily recovered and purified, ready to be used in further reactions.     

Acidity and Structure of Ca-Doped V2O5/ZrO2 Catalysts

Acidity and structure of Ca-doped V₂O₅/ZrO₂ catalysts have been studied by FTIR. Both Lewis and Brønsted acidity decreased with Ca loading. New surface vanadate species seemed to be formed by Ca addition.     

Diastereoselective synthesis of trans-trifluoromethyl-β-lactams and α-alkyl-β-trifluoromethyl-β-amino esters

The diastereoselective synthesis of β-lactams was examined from N-tosyl-1-chloro-2,2,2-trifluoroethylamine 3 and various nonactivated aliphatic acid chlorides in the presence of a Brønsted base. The mild reaction conditions allowed to get trifluoromethyl-β-lactams in good yields with high trans-diastereo selectivity. In addition, we also demonstrated that ring-opening of β-lactams easily provided α-alkyl-β-trifluoromethyl-β-amino esters.     

Development of N,N-bis(perfluoroalkanesulfonyl)squaramides as new strong Brønsted acids and their application to organic reactions

New strong Brønsted acids derived from a squaric acid scaffold bearing different perfluoroalkanesulfonyl groups have been developed and applied to several organic reactions. These squaramides are bench-stable and exhibit much higher reactivities in several organic reactions than squaric acid itself. N,N-Bis(trifluoromethanesulfonyl)squaramide 2a was applied to the Mukaiyama aldol reaction and Mukaiyama Michael reaction. Mechanistic studies revealed that the Brønsted acid might be the predominant catalyst through direct protonation of carbonyl compound by the acid itself rather than the silylated Brønsted acid. The utility of this acid 2a was further extended to Hosomi-Sakurai allylation of aldehydes and a carbonyl-ene reaction. Furthermore, other squaramides 2b and c bearing longer perfluoroalkyl chains have been developed, which are also bench-stable and displayed similar reactivities with squaramide 2a in several organic reactions.     

Palladium-catalyzed asymmetric hydrogenation of simple ketones activated by Brønsted acids

Homogeneous Pd(OCOCF₃)₂/(R)-C₄-TunePhos has been successfully applied in the asymmetric hydrogenation of simple ketones activated by catalytic amount of Brønsted acid with up to 88% ee.     

Conjugated polymers as photoredox catalysts: a new catalytic system using visible light to promote aryl aldehyde pinacol couplings

The conjugated polymer poly-(p)-phenylene (PPP) was synthesized and used as a photoredox catalyst to promote pinacol coupling of aryl-aldehydes with visible light. The reaction required the use of a sacrificial electron donor (Et₃N), and was accelerated by the addition of Lewis and Brønsted acids. A distinct advantage of this photocatalytic system is the robust nature of the system, which is not overly sensitive to impurities, oxygen, or temperature, and proceeds cleanly with few side reactions. As a comparison with the PPP system, the reactivity of Ru(bpy)₃Cl₂, a popular photoredox catalyst was compared. The PPP system was superior to the Ru(bpy)₃Cl₂ for the pinacol couplings in both rate and yield.     

General-buffer catalysis of the reaction of N-(hydroxymethyl)benzamide: a new pathway for the aqueous reaction of carbinolamides

The second-order rate constants for the general-buffer catalyzed breakdown of N-(hydroxymethyl)benzamide (1) in water at 25 °C, I = 1.0 (KCl) by pivalic, acetic, chloroacetic, and dichloroacetic acid were determined by initial rates. The observed rate increased with increasing amounts of the acidic form of the buffer and a Brønsted correlation of α = 0.35 was determined. The results presented here, represent the first evidence for a general-buffer catalytic mechanism for the aqueous reaction of 1 and for carbinolamides in general.     

Heptadecafluorooctanesulfonic acid (C8F17SO3H) catalyzed intramolecular hydroamination of olefinic sulfonamides in fluorous biphase system (FBS)

A practical, efficient, and environmentally benign intramolecular hydroamination of olefinic sulfonamides was carried out in fluorous biphase system (FBS) using commercially available heptadecafluorooctanesulfonic acid (C₈F₁₇SO₃H) as a catalyst and perfluorodecaline (C₁₀F₁₈, cis- and trans- mixture) as a fluorous solvent to produce the corresponding cyclic products in good yields. The Brønsted acid of C₈F₁₇SO₃H is easily recovered and recycled at least five times.     

Synthesis of highly substituted indene derivatives by Brønsted acid catalyzed Friedel–Crafts reaction of homoallylic alcohols

An efficient synthetic method to prepare highly substituted indenes in moderate to excellent yields that relies on Brønsted acid catalyzed Friedel–Crafts reaction of homoallylic alcohols under mild conditions is described.     

Ring-opening reaction of methylenecyclopropanes with LiCl, LiBr or NaI in acetic acid

The methylenecyclopropanes 1 react with LiCl, LiBr or NaI at 80 °C to give the corresponding gem-disubstituted homoallylic halides 2 in good to excellent yields in acetic acid. In some cases, the ring-opening reaction can be completed within 5 min to give the corresponding gem-disubstituted homoallylic halides in high yields.