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Matthew Nava Irina V. Stoyanova Dr. Steven Cummings Prof. Dr. Evgenii S. Stoyanov Prof. Dr. Christopher A. Reed 《Angewandte Chemie (International ed. in English)》2014,53(4):1131-1134
What is the strongest acid? Can a simple Brønsted acid be prepared that can protonate an alkane at room temperature? Can that acid be free of the complicating effects of added Lewis acids that are typical of common, difficult‐to‐handle superacid mixtures? The carborane superacid H(CHB11F11) is that acid. It is an extremely moisture‐sensitive solid, prepared by treatment of anhydrous HCl with [Et3Si? H? SiEt3][CHB11F11]. It adds H2O to form [H3O][CHB11F11] and benzene to form the benzenium ion salt [C6H7][CHB11F11]. It reacts with butane to form a crystalline tBu+ salt and with n‐hexane to form an isolable hexyl carbocation salt. Carbocations, which are thus no longer transient intermediates, react with NaH either by hydride addition to re‐form an alkane or by deprotonation to form an alkene and H2. By protonating alkanes at room temperature, the reactivity of H(CHB11F11) opens up new opportunities for the easier study of acid‐catalyzed hydrocarbon reforming. 相似文献
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《Helvetica chimica acta》2017,100(3)
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. 相似文献
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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). 相似文献
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A General Access to Propargylic Ethers through Brønsted Acid Catalyzed Alkynylation of Acetals and Ketals with Trifluoroborates
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Matthew Baxter Prof. Dr. Yuri Bolshan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(39):13535-13538
A general Brønsted acid catalyzed methodology for the alkynylation of acetals and ketals with alkynyltrifluoroborate salts has been developed. The reaction proceeds rapidly to afford valuable synthetic building block propargylic ethers in good to excellent yields. Unlike Lewis acid catalyzed transformations of trifluoroborates, this approach does not proceed via unstable organodifluoroborane intermediate. As a result, the developed methodology features excellent functional group tolerance and good atom economy. 相似文献
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Dr. Vijay N. Wakchaure Philip S. J. Kaib Markus Leutzsch Prof. Dr. Benjamin List 《Angewandte Chemie (International ed. in English)》2015,54(40):11852-11856
A chiral disulfonimide (DSI)‐catalyzed asymmetric reduction of N‐alkyl imines with Hantzsch esters as a hydrogen source in the presence of Boc2O has been developed. The reaction delivers Boc‐protected N‐alkyl amines with excellent yields and enantioselectivity. The method tolerates a large variety of alkyl amines, thus illustrating potential for a general reductive cross‐coupling of ketones with diverse amines, and it was applied in the synthesis of the pharmaceuticals (S)‐Rivastigmine, NPS R‐568 Hydrochloride, and (R)‐Fendiline. 相似文献
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Straightforward Synthesis of the Brønsted Acid hfipOSO3H and its Application for the Synthesis of Protic Ionic Liquids
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Dr. Witali Beichel Dipl.‐Chem. Johann M. U. Panzer B. Sc. Julian Hätty Dipl.‐Chem. Xiaowei Ye Dr. Daniel Himmel Prof. Dr. Ingo Krossing 《Angewandte Chemie (International ed. in English)》2014,53(26):6637-6640
The easily accessible hexafluoroisopropoxysulfuric acid ( 1 , hfipOSO3H ; hfip=C(H)(CF3)2) was synthesized by the reaction of hexafluoroisopropanol and chlorosulfonic acid on the kilogram scale and isolated in 98 % yield. The calculated gas‐phase acidity (GA) value of 1 is 58 kJ mol?1 lower in ΔG° than that of sulfuric acid (GA value determined by a CCSD(T)‐MP2 compound method). Considering the gas‐phase dissociation constant as a measure for the intrinsic molecular acid strength, a hfipOSO3H molecule is more than ten orders of magnitude more acidic than a H2SO4 molecule. The acid is a liquid at room temperature, distillable at reduced pressure, stable for more than one year in a closed vessel, reactive towards common solvents, and decomposes above 180 °C. It is a versatile compound for further applications, such as the synthesis of ammonium‐ and imidazolium‐based air‐ and moisture‐stable protic ionic liquids (pILs). Among the six synthesized ionic compounds, five are pILs with melting points below 100 °C and three of them are liquids at nearly room temperature. The conductivities and viscosities of two representative ILs were investigated in terms of Walden plots, and the pILs were found to be little associated ILs, comparable to conventional aprotic ILs. 相似文献
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Direct N‐Glycofunctionalization of Amides with Glycosyl Trichloroacetimidate by Thiourea/Halogen Bond Donor Co‐Catalysis
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Dr. Yusuke Kobayashi Yuya Nakatsuji Shanji Li Dr. Seiji Tsuzuki Prof. Dr. Yoshiji Takemoto 《Angewandte Chemie (International ed. in English)》2018,57(14):3646-3650
Using a halogen bond (XB) donor and Schreiner's thiourea as cooperative catalysts, various amides, including the asparagine residues of several peptides, were directly coupled with glycosyl trichloroacetimidates to give unique N‐acylorthoamides in good yields. Synthetic applications of N‐acylorthoamides, including rearrangement to the corresponding β‐N‐glycoside, were also demonstrated. 相似文献
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Brønsted Acid Enabled Nickel‐Catalyzed Hydroalkenylation of Aldehydes with Styrene and its Derivatives
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Xing‐Wang Han Tao Zhang Yan‐Long Zheng Wei‐Wei Yao Jiang‐Fei Li You‐Ge Pu Prof. Dr. Mengchun Ye Qi‐Lin Zhou 《Angewandte Chemie (International ed. in English)》2018,57(18):5068-5071
A Brønsted acid enabled nickel‐catalyzed hydroalkenylation of aldehydes and styrene derivatives has been developed. The Brønsted acid acts as a proton shuttle to transfer a proton from the alkene to the aldehyde, thereby leading to an economical and byproduct‐free coupling. A series of synthetically useful allylic alcohols were obtained through one‐step reactions from readily available styrene derivatives and aliphatic aldehydes in up to 88 % yield and with high linear selectivity. 相似文献
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Dr. Wenlong Yang Dr. Jorge H. S. K. Monteiro Prof. Ana de Bettencourt‐Dias Prof. Vincent J. Catalano Prof. Wesley A. Chalifoux 《Angewandte Chemie (International ed. in English)》2016,55(35):10427-10430
The design of a relatively simple and efficient method to extend the π‐conjugation of readily available aromatics in one‐dimension is of significant value. In this paper, pyrenes, peropyrenes, and teropyrenes were synthesized through a double or quadruple benzannulation reaction of alkynes promoted by Brønsted acid. This novel method does not involve cyclodehydrogenation (oxidative aryl–aryl coupling) to arrive at the newly incorporated large arene moieties. All of the target compounds were synthesized in moderate to good yields and were fully characterized with the structures unambiguously confirmed by X‐ray crystallography. As expected, photophysical characterization clearly shows increasing red‐shifts as a function of extended conjugation within the fused ring systems. 相似文献
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Gold(I)/Chiral Brønsted Acid Catalyzed Enantioselective Hydroamination–Hydroarylation of Alkynes: The Effect of a Remote Hydroxyl Group on the Reactivity and Enantioselectivity
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Valmik S. Shinde Manoj V. Mane Dr. Kumar Vanka Arijit Mallick Dr. Nitin T. Patil 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(3):975-979
The catalytic enantioselective hydroamination–hydroarylation of alkynes under the catalysis of (R3P)AuMe/(S)‐3,3′‐bis(2,4,6‐triisopropylphenyl)‐1,1′‐binaphthyl‐2,2′‐diyl hydrogenphosphate ((S)‐TRIP) is reported. The alkyne was reacted with a range of pyrrole‐based aromatic amines to give pyrrole‐embedded aza‐heterocyclic scaffolds bearing a quaternary carbon center. The presence of a hydroxyl group in the alkyne tether turned out to be very crucial for obtaining products in high yields and enantioselectivities. The mechanism of enantioinduction was established by carefully performing experimental and computational studies. 相似文献
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Dr. Steven Cummings Prof. Dr. Hrant P. Hratchian Prof. Dr. Christopher A. Reed 《Angewandte Chemie (International ed. in English)》2016,55(4):1382-1386
The strongest carborane acid, H(CHB11F11), protonates CO2 while traditional mixed Lewis/Brønsted superacids do not. The product is deduced from IR spectroscopy and calculation to be the proton disolvate, H(CO2)2+. The carborane acid H(CHB11F11) is therefore the strongest known acid. The failure of traditional mixed superacids to protonate weak bases such as CO2 can be traced to a competition between the proton and the Lewis acid for the added base. The high protic acidity promised by large absolute values of the Hammett acidity function (H0) is not realized in practice because the basicity of an added base is suppressed by Lewis acid/base adduct formation. 相似文献
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Cationic ring‐opening polymerization of trimethylene carbonate to α,ω‐dihydroxy telechelic and star‐shaped polycarbonates catalyzed by reusable o‐benzenedisulfonimide
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Hao Wu Yufeng Ji Zhenjiang Li Xin Wang Qiguo Zhang Saide Cui Wenzhuo Wu Jingjing Liu Kai Guo 《Journal of polymer science. Part A, Polymer chemistry》2015,53(6):729-736
Cationic ring‐opening polymerization of trimethylene carbonate using o‐benzenedisulfonimide as a reusable catalyst under mild conditions was described. The polymerization proceeded homogeneously without decarboxylation and poly(trimethylene carbonates) (PTMCs) were synthesized with well‐controlled molecular weights and narrow polydispersities (Mw/Mn = 1.12–1.18). The spectra of 1H‐NMR, SEC, and MALDI–ToF MS clearly demonstrated the incorporation of the initiator residue into the polymer chains and the controlled/living nature of the polymerizations. Furthermore, the catalyst can be easily recovered, and its efficiency was fully retained. In addition, 1,3‐propanediol, 1,1,1‐trimethylolpropane, and pentaerythritol were successfully used as initiators to produce telechelic and star‐shaped polycarbonates which were determined by intrinsic viscosity experiments. The number of arms estimated by the shrinking factors ( ) were 2.0, 2.6, and 3.5, respectively, indicating the successful syntheses of the two‐, three‐, and four‐armed PTMCs. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 729–736 相似文献
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Aminomethylation of Enals through Carbene and Acid Cooperative Catalysis: Concise Access to β2‐Amino Acids
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Dr. Jianfeng Xu Xingkuan Chen Dr. Ming Wang Pengcheng Zheng Bao‐An Song Prof. Dr. Yonggui Robin Chi 《Angewandte Chemie (International ed. in English)》2015,54(17):5161-5165
A convergent, organocatalytic asymmetric aminomethylation of α,β‐unsaturated aldehydes by N‐heterocyclic carbene (NHC) and (in situ generated) Brønsted acid cooperative catalysis is disclosed. The catalytically generated conjugated acid from the base plays dual roles in promoting the formation of azolium enolate intermediate, formaldehyde‐derived iminium ion (as an electrophilic reactant), and methanol (as a nucleophilic reactant). This redox‐neutral strategy is suitable for the scalable synthesis of enantiomerically enriched β2‐amino acids bearing various substituents. 相似文献
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