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1.
Cuihuan Geng Rongxiu Zhu Mingxia Li Tongxiang Lu Prof. Steven E. Wheeler Prof. Chengbu Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(48):15833-15839
The pairing of transition metal catalysis with the reagent Selectfluor (F‐TEDA–BF4) has attracted considerable attention due to its utility in myriad C?C and C?heteroatom bond‐forming reactions. However, little mechanistic information is available for Selectfluor‐mediated transition metal‐catalyzed reactions and controversy surrounds the precise role of Selectfluor in these processes. We present herein a systematic investigation of homogeneous Au‐catalyzed oxidative C?O bond‐forming reactions using density functional theory calculations. Currently, Selectfluor is thought to serve as an external oxidant in AuI/AuIII catalysis. However, our investigations suggest that these reactions follow a newly proposed mechanism in which Selectfluor functions as an electrophilic fluorinating reagent involved in a fluorination/defluorination cycle. We have also explored Selectfluor‐mediated gold‐catalyzed homocoupling reactions, which, when cyclopropyl propargylbenzoate is used as a substrate, lead to an unexpected byproduct. 相似文献
2.
Steven Bloom Desta Doro Bume Cody Ross Pitts Prof. Dr. Thomas Lectka 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(22):8060-8063
To expand upon the recent pioneering reports of catalyzed sp3 C?H fluorination methods, the next rational step is to focus on directing “radical‐based fluorination” more effectively. One potential solution entails selective C?C bond activation as a prelude to selective fluorination. Herein, we report the tandem photocatalyzed ring‐opening/fluorination reactions of cyclopropanols by 1,2,4,5‐tetracyanobenzene (TCB) and Selectfluor to afford a process tantamount to site‐selective β‐fluorination of carbonyl‐containing compounds. This new approach provides a synthetically mild and operationally simple route to otherwise difficult‐to‐prepare β‐fluorinated products in good yields and with good‐to‐excellent regioselectivity. Remarkably, substrates that contain other usually reactive (e.g., benzylic) sites undergo ring‐opening fluorination preferably. The versatility of this method to give cyclic β‐fluorides from tertiary cyclopropanols and γ‐fluoro alcohols is also highlighted. 相似文献
3.
Silver‐Catalyzed Oxidative Activation of Benzylic CH Bonds for the Synthesis of Difluoromethylated Arenes
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Peng Xu Shuo Guo Liyan Wang Prof. Dr. Pingping Tang 《Angewandte Chemie (International ed. in English)》2014,53(23):5955-5958
A mild and catalytic method to form difluoromethylated arenes through the activation of benzylic C? H bonds has been developed. Utilizing AgNO3 as the catalyst, various arenes with diverse functional groups undergo activation/fluorination of benzylic C? H bonds with commercially available Selectfluor reagent as a source of fluorine in aqueous solution. The reaction is operationally simple and amenable to gram‐scale synthesis. 相似文献
4.
Byung Joo Lee Kimberly S. DeGlopper Tehshik P. Yoon 《Angewandte Chemie (International ed. in English)》2020,59(1):197-202
Methods that enable the direct C?H alkoxylation of complex organic molecules are significantly underdeveloped, particularly in comparison to analogous strategies for C?N and C?C bond formation. In particular, almost all methods for the incorporation of alcohols by C?H oxidation require the use of the alcohol component as a solvent or co‐solvent. This condition limits the practical scope of these reactions to simple, inexpensive alcohols. Reported here is a photocatalytic protocol for the functionalization of benzylic C?H bonds with a wide range of oxygen nucleophiles. This strategy merges the photoredox activation of arenes with copper(II)‐mediated oxidation of the resulting benzylic radicals, which enables the introduction of benzylic C?O bonds with high site selectivity, chemoselectivity, and functional‐group tolerance using only two equivalents of the alcohol coupling partner. This method enables the late‐stage introduction of complex alkoxy groups into bioactive molecules, providing a practical new tool with potential applications in synthesis and medicinal chemistry. 相似文献
5.
2‐Methylphenyl ketones undergo site‐selective acylation at the benzylic position when treated with acid anhydride under UV irradiation in the presence of a palladium catalyst. The benzoyl carbonyl group serves as the photo‐directing group so that the ortho benzylic C?H bond is activated site‐selectively. 相似文献
6.
Yu‐Feng Liu Dan‐Dan Zhai Xiang‐Yu Zhang Prof. Dr. Bing‐Tao Guan 《Angewandte Chemie (International ed. in English)》2018,57(27):8245-8249
Direct functionalization of the benzylic C?H bond of diarylmethanes is an important strategy for the synthesis of diarylmethine‐containing compounds. However, the methods developed to date for this purpose require a stoichiometric amount (usually more) of either a strong base or an oxidant. Reported here is the first catalytic benzylic C?H bond addition of diarylmethanes to styrenes and conjugated dienes. A potassium zincate complex, generated from potassium benzyl and zinc amide, acts as a catalyst and displays good activity and chemoselectivity. Considering the atom economy of the reaction and the ready availability of the catalyst, this reaction constitutes a practical, efficient method for diarylalkane synthesis. 相似文献
7.
Synthesis of Highly Substituted γ‐Butyrolactones by a Gold‐Catalyzed Cascade Reaction of Benzyl Esters
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Maria Camila Blanco Jaimes Alexander Ahrens Daniel Pflästerer Dr. Matthias Rudolph Prof. Dr. A. Stephen K. Hashmi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(1):427-433
Easily accessible benzylic esters of 3‐butynoic acids in a gold‐catalyzed cyclization/rearrangement cascade reaction provided 3‐propargyl γ‐butyrolactones with the alkene and the carbonyl group not being conjugated. Crossover experiments showed that the formation of the new C?C bond is an intermolecular process. Initially propargylic–benzylic esters were used, but alkyl‐substituted benzylic esters worked equally well. In the case of the propargylic–benzylic products, a simple treatment of the products with aluminum oxide initiated a twofold tautomerization to the allenyl‐substituted γ‐butyrolactones with conjugation of the carbonyl group, the olefin, and the allene. The synthetic sequence can be conducted stepwise or as a one‐pot cascade reaction with similar yields. Even in the presence of the gold catalyst the new allene remains intact. 相似文献
8.
Gold‐Catalyzed Fluorination–Hydration: Synthesis of α‐Fluorobenzofuranones from 2‐Alkynylphenol Derivatives
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Qiang Wang Yu Jiang Run Sun Prof. Dr. Xiang‐Ying Tang Prof. Dr. Min Shi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(41):14739-14745
The AuI‐catalyzed fluorination–hydration of 2‐alkynylphenol derivatives in the presence of Selectfluor [1‐chloromethyl‐4‐fluoro‐1,4‐diazoniabicyclo‐[2.2.2]octane bis(tetrafluoroborate)] has been developed. This method provides straightforward access to α‐fluorobenzofuranones with the construction of C?O, C=O, and C?F bonds in a single step on the basis of an AuI/AuIII redox catalytic cycle. Several control experiments, including the asymmetric variant of this reaction, were also conducted to gain insight into the reaction mechanism. 相似文献
9.
Abhishek Dewanji Patricia E. Krach Magnus Rueping 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(11):3604-3608
A dual catalytic protocol for the direct arylation of non‐activated C(sp3)?H bonds has been developed. Upon photochemical excitation, the excited triplet state of a diaryl ketone photosensitizer abstracts a hydrogen atom from an aliphatic C?H bond. This inherent reactivity was exploited for the generation of benzylic radicals which subsequently enter a nickel catalytic cycle, accomplishing the benzylic arylation. 相似文献
10.
Friedel–Crafts Reaction of Benzyl Fluorides: Selective Activation of CF Bonds as Enabled by Hydrogen Bonding
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Pier Alexandre Champagne Yasmine Benhassine Justine Desroches Prof. Jean‐François Paquin 《Angewandte Chemie (International ed. in English)》2014,53(50):13835-13839
A Friedel–Crafts benzylation of arenes with benzyl fluorides has been developed. The reaction produces 1,1‐diaryl alkanes in good yield under mild conditions without the need for a transition metal or a strong Lewis acid. A mechanism involving activation of the C? F bond through hydrogen bonding is proposed. This mode of activation enables the selective reaction of benzylic C? F bonds in the presence of other benzylic leaving groups. 相似文献
11.
3(2H)‐Furanones are efficiently generated from 3‐alkynyl oxireno[2,3‐b]chromenones by an Au/DDQ‐catalyzed domino reaction through a pathway composed of cyclization, C? C cleavage, nucleophilic addition, oxidation, and nucleophilic addition. It was found that stoichiometric AuCl3 or catalytic Au with stoichiometric DDQ can oxidize the benzylic sp3 C? H bond to facilitate nucleophilic addition. 相似文献
12.
N‐Heterocyclic Carbene Iron(III) Porphyrin‐Catalyzed Intramolecular C(sp3)–H Amination of Alkyl Azides
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Ka‐Pan Shing Dr. Yungen Liu Dr. Bei Cao Dr. Xiao‐Yong Chang Tingjie You Prof. Dr. Chi‐Ming Che 《Angewandte Chemie (International ed. in English)》2018,57(37):11947-11951
Metal‐catalyzed intramolecular C?H amination of alkyl azides constitutes an appealing approach to alicyclic amines; challenges remain in broadening substrate scope, enhancing regioselectivity, and applying the method to natural product synthesis. Herein we report an iron(III) porphyrin bearing axial N‐heterocyclic carbene ligands which catalyzes the intramolecular C(sp3)–H amination of a wide variety of alkyl azides under microwave‐assisted and thermal conditions, resulting in selective amination of tertiary, benzylic, allylic, secondary, and primary C?H bonds with up to 95 % yield. 14 out of 17 substrates were cyclized selectively at C4 to give pyrrolidines. The regioselectivity at C4 or C5 could be tuned by modifying the reactivity of the C5–H bond. Mechanistic studies revealed a concerted or a fast re‐bound mechanism for the amination reaction. The reaction has been applied to the syntheses of tropane, nicotine, cis‐octahydroindole, and leelamine derivatives. 相似文献
13.
Dr. Xuesong Wu Yan Zhao Prof. Dr. Haibo Ge 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(31):9530-9533
Intramolecular dehydrogenative cyclization of aliphatic amides was achieved on unactivated sp3 carbon atoms by a nickel‐catalyzed C?H bond functionalization process with the assistance of a bidentate directing group. The reaction favors the C?H bonds of β‐methyl groups over the γ‐methyl or β‐methylene groups. Additionally, a predominant preference for the β‐methyl C?H bonds over the aromatic sp2 C?H bonds was observed. Moreover, this process also allows for the effective functionalization of benzylic secondary sp3 C?H bonds. 相似文献
14.
Iridium‐Catalyzed Regioselective Silylation of Aromatic and Benzylic CH Bonds Directed by a Secondary Amine
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Dr. Qian Li Prof. Dr. Matthias Driess Prof. Dr. John F. Hartwig 《Angewandte Chemie (International ed. in English)》2014,53(32):8471-8474
Reported herein is an iridium‐catalyzed, regioselective silylation of the aromatic C? H bonds of benzylamines and the benzylic C? H bonds of 2,N‐dialkylanilines. In this process, (hydrido)silyl amines, generated in situ by dehydrogenative coupling of benzylamine or aniline with diethylsilane, undergo selective silylation at the C? H bond γ to the amino group. The products of this silylation are suitable for subsequent oxidation, halogenation, and cross‐coupling reactions to deliver benzylamine and arylamine derivatives. 相似文献
15.
Eiji Ihara Takao Wake Naoki Mokume Tomomichi Itoh Kenzo Inoue 《Journal of polymer science. Part A, Polymer chemistry》2006,44(19):5661-5671
α,α‐Dibromotoluene 1 was found to be polymerized by the reaction with excess Mg to give poly(phenylmethylene)s 2 , whose main chains were partially dehydrogenated to carbon–carbon double bonds (C?C). The C?Cs in 2 can be brominated by treatment with Br2. The polymerization mechanism was presumed to include the formation of Grignard reagents of various species with benzylic C? Br bonds and the nucleophilic attacks of the Grignard reagents to various compounds with benzylic C? Br bonds. Copolymerization of 1 with dichlorodimethylsilane successfully proceeded. Mg/Cu‐mediated copolycondensation of 1 with 1,6‐dibromohexane proceeded to give polymers that have similar compositions to those of random copolymers of ethylene and styrene. © 2006Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5661–5671, 2006 相似文献
16.
Dan‐Dan Zhai Xiang‐Yu Zhang Yu‐Feng Liu Lei Zheng Prof. Dr. Bing‐Tao Guan 《Angewandte Chemie (International ed. in English)》2018,57(6):1650-1653
The benzylic functionalization of alkylpyridines is an important pathway for pyridine derivatives synthesis. The reaction partners, however, were mostly limited to highly reactive polar electrophiles. Herein, we report a potassium amide‐catalyzed selective benzylic C?H bond addition of alkylpyridines to styrenes. Potassium bis(trimethylsilyl)amide (KHMDS), a readily available Brønsted base, showed excellent catalytic activity and chemoselectivity. A series of alkylpyridine derivatives, including benzylic quaternary carbon substituted pyridines, were obtained in good to high yield. Preliminary mechanistic studies revealed that the deprotonation equilibrium is probably responsible for the excellent selectivity. 相似文献
17.
Kevin M. Arendt Prof. Abigail G. Doyle 《Angewandte Chemie (International ed. in English)》2015,54(34):9876-9880
A new substrate class for nickel‐catalyzed C(sp3) cross‐coupling reactions is reported. α‐Oxy radicals generated from benzylic acetals, TMSCl, and a mild reductant can participate in chemoselective cross‐coupling with aryl iodides using a 2,6‐bis(N‐pyrazolyl)pyridine (bpp)/Ni catalyst. The mild, base‐free conditions are tolerant of a variety of functional groups on both partners, thus representing an attractive C? C bond‐forming approach to dialkyl ether synthesis. Characterization of a [(bpp)NiCl] complex relevant to the proposed catalytic cycle is also described. 相似文献
18.
Dieter Seebach W. Bernd Schweizer Stefan Grimme Christian Mück‐Lichtenfeld 《Helvetica chimica acta》2010,93(1):1-16
The PF6 salts of 5‐benzyl‐1‐isopropylidene‐ and 5‐benzyl‐1‐cinnamylidene‐3‐methylimidazolidin‐4‐ones 1 (Scheme) with various substituents in the 2‐position have been prepared, and single crystals suitable for X‐ray structure determination have been obtained of 14 such compounds, i.e., 2 – 10 and 12 – 16 (Figs. 2–5). In nine of the structures, the Ph ring of the benzyl group resides above the heterocycle, in contact with the cis‐substituent at C(2) (staggered conformation A ; Figs. 1–3); in three structures, the Ph ring lies above the iminium π‐plane (staggered conformation B ; Figs. 1 and 4); in two structures, the benzylic C? C bond has an eclipsing conformation ( C ; Figs. 1 and 5) which places the Ph ring simultaneously at a maximum distance with its neighbors, the CO group, the N?C‐π‐system, and the cis‐substituent at C(2) of the heterocycle. It is suggested by a qualitative conformational analysis (Fig. 6) that the three staggered conformations of the benzylic C? C bond are all subject to unfavorable steric interactions, so that the eclipsing conformation may be a kind of ‘escape’. State‐of‐the‐art quantum‐chemical methods, with large AO basic sets (near the limit) for the single‐point calculations, were used to compute the structures of seven of the 14 iminium ions, i.e., 3, 4 / 12, 5 – 7, 13 , and 16 (Table) in the two staggered conformations, A and B , with the benzylic Ph group above the ring and above the iminium π‐system, respectively. In all cases, the more stable computed conformer (‘isolated‐molecule’ structure) corresponds to the one present in the crystal (overlay in Fig. 7). The energy differences are small (≤2 kcal/mol) which, together with the result of a potential‐curve calculation for the rotation around the benzylic C? C bond of one of the structures, 16 (Fig. 8), suggests that the benzyl group is more or less freely rotating at ambident temperatures. The importance of intramolecular London dispersion (benzene ring in ‘contact’ with the cis‐substituent in conformation A ) for DFT and other quantum‐chemical computations is demonstrated; the benzyl‐imidazolidinones 1 appear to be ideal systems for detecting dispersion contributions between a benzene ring and alkyl or aryl CH groups. Enylidene ions of the type studied herein are the reactive intermediates of enantioselective organocatalytic conjugate additions, Diels–Alder reactions, and many other transformations involving α,β‐unsaturated carbonyl compounds. Our experimental and theoretical results are discussed in view of the performance of 5‐benzyl‐imidazolidinones as enantioselective catalysts. 相似文献
19.
Ronan Rocaboy Ioannis Anastasiou Olivier Baudoin 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(41):14767-14770
The intramolecular coupling of two C(sp3)?H bonds to forge a C(sp3)?C(sp3) bond is enabled by 1,4‐Pd shift from a trisubstituted aryl bromide. Contrary to most C(sp3)?C(sp3) cross‐dehydrogenative couplings, this reaction operates under redox‐neutral conditions, with the C?Br bond acting as an internal oxidant. Furthermore, it allows the coupling between two moderately acidic primary or secondary C?H bonds, which are adjacent to an oxygen or nitrogen atom on one side, and benzylic or adjacent to a carbonyl group on the other side. A variety of valuable fused heterocycles were obtained from easily accessible ortho‐bromophenol and aniline precursors. The second C?H bond cleavage was successfully replaced with carbonyl insertion to generate other types of C(sp3)‐C(sp3) bonds. 相似文献
20.
三氟甲磺酸被发现能够高效地活化(SP3)碳-氟键。因此,在其催化作用下,室温时含三氟甲基的芳香化合物与苯反应得到二苯甲酮类化合物。在同样的Brønsted 酸催化下,其中一些含三氟甲基的芳香化合物亦可发生分子内的芳基化反应,而此时分子间的芳基化受抑制。强的氢氟间的相互作用或氢键作用,被认为对该Brønsted 酸参与碳氟键活化的反应起了重要作用。 相似文献