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![Pd-catalyzed alkoxylation of benzo[h]quinoline.](profile/Bing-Feng-Shi/publication/268750397/figure/fig10/AS:267864229806124@1440875217758/Pd-catalyzed-alkoxylation-of-benzohquinoline_Q320.jpg)
The formation of C–O bonds is one of the fundamental transformations in organic chemistry. This digest summarizes recent advances in transition-metal-catalyzed etherification of unactivated C–H bonds. Etherification reactions with different directing groups and catalyst systems via C(sp2)–H and C(sp3)–H bonds activation are described.
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Machine learning has proven to be a powerful technique during the past decades. Artificial neural network (ANN), as one of the most popular machine learning algorithms, has been widely applied to various areas. However, their applications for catalysis were not well-studied until recent decades. In this review, we aim to summarize the applications...
Single-atom catalysts (SACs) with individual and isolated metal atoms anchored to supports can act as active centers. Single-atom catalysis is powerful and attractive because SACs have demonstrated distinguishing performances, such as drastic cost-reduction, notable catalytic activity, and selectivity. Herein, we firstly introduce SAC, including th...
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... As expected, no product was formed without Pd (entry 3) and the use of other Pd complexes, such as Pd(OAc) 2 , led to lower efficiency (entry 4). The reaction showed a low conversion without the phosphine ligand, suggesting its important role in stabilizing Pd(0); while PPh 3 only slightly reduced the yield, the more electron-deficient P(2-pyr) 3 ligand gave a much lower yield (entries 5-7). The use of the C7-bromo-substituted NBE (N1) proved to be essential because, except for simple NBE (N2) which afforded a 5% yield (entries 8 and 9), other NBEs with various substitutions all gave only a trace amount of the desired product (Supplementary Table 1). ...
Oxygen-substituted arenes widely exist in biologically important molecules and can serve as versatile handles to install other functional groups. However, direct and site-selective installation of oxygen groups to common aromatic compounds remains challenging, especially when additional arene functionalization is simultaneously required. Current arene C−H oxidation strategies generally require directing groups or precisely prefunctionalized substrates to control site-selectivity. While palladium/norbornene cooperative catalysis is promising for site-specific arene vicinal difunctionalization through simultaneous reactions with an electrophile and a nucleophile, the electrophile scope has been limited to species based on relatively ‘soft’ elements, such as carbon, nitrogen and sulfur. Here we report the development of an ortho oxygenation reaction with common aryl halides to rapidly deliver diverse aryl ethers. The coupling of the ‘hard’ oxygen electrophile is enabled by a stable, polarity-reversed, conformationally predistorted N−O reagent and facilitated by a C7-bromo-substituted norbornene mediator. Mechanistic studies reveal a unique SN2-type pathway between the N−O reagent as the oxygen electrophile and an electron-rich Pd(II) nucleophile.
... Indeed, fluorinated ethers [71,[141][142][143][144][145][146][147][148][149][150][151][152][153] are key compounds, with especially molecules substituted with the 2,2,2-trifluoroethoxy moiety (OCH 2 CF 3 ), an important fluorinated group found in several bioactive compounds such as flecanide [154,155] and lansoprazole [156], as flagship molecules. Although the transition-metal-catalyzed hydroxylation and alkoxylation have been studied especially under palladium catalysis [157,158], the direct dehydrogenative 2,2,2trifluoroethoxylation of (hetero)arenes, often using 2,2,2-trifluoroethanol as a readily available, inexpensive, and green fluorination source [159,160], is still underexplored. ...
The last decade has witnessed the emergence of innovative synthetic tools for the synthesis of fluorinated molecules. Among these approaches, the transition-metal-catalyzed functionalization of various scaffolds with a panel of fluorinated groups (XR F , X = S, Se, O) offered straightforward access to high value-added compounds. This review will highlight the main advances made in the field with the transition-metal-catalyzed functionalization of C(sp ² ) and C(sp ³ ) centers with SCF 3 , SeCF 3 , or OCH 2 CF 3 groups among others, by C–H bond activation. The scope and limitations of these transformations are discussed in this review.
... [10] After that, variousc atalytic CÀHb ond alkoxylation reactions had been extensively studied with transition metal catalysts for the ether synthesis. [11] However,t he substrates scope of thesem ethods were greatly limited to the arenes with directing groups such as hydroxyl groups (Intramolecular CÀOb ond formation), [12] bidentate chelating groups, [13] and strong coordinated Na tom containing groups [14] (pyridine, imine, azo, etc.). [15] The catalytic alkoxylation of benzamides has seldom been reportede xpect for several special examples such as N-methoxybenzamide, N-tosylcarboxamide and ketostabilised iminophosphoranes (Scheme 1, a-c). ...
... Potassium persulfate could also work as an oxidant, andg ave the product in a moderate yield of 59 %( Ta ble 1, entry 10). Some other oxidants such as BPO, DTBP,B Qa nd PhI(OAc) 2 were subjected to the reaction, and the methoxylation product was obtained in much lower yields (Table 1, entries [11][12][13][14]. Carried out the reaction in methanol,t he methoxylation product was obtainedi nalower yield of 45 %( Ta ble 1, entry 15). ...
Transition metal-catalyzed C-H bond alkoxylation reactions represent a direct and efficient strategy for the aryl ethers synthesis. However, the substrate scope of these methods so far was greatly limited. Herein, we reported the first catalyzed ortho-alkoxylation of tertiary benzamides. Using Pd(OAc)2 as a catalyst and H2SO4 as a key additive, benzamides with various functional groups underwent the alkoxylation efficiently with alcohols.
... In the past decade, the transition-metal-catalyzed Ullmann-type coupling reaction has emerged as an effective method, allowing the synthesis of phenols and aryl thiols from aryl halides through C-O and C-S bond formation, respectively [5][6][7]. Very recently, the C-H activation has made revolutionary advances in organic synthesis because it allows an access to functionalized products from simple arenes, avoiding their pre-functionalization [8][9][10]. The synthesis of phenols has greatly benefited from C-H activation, but the application in the synthesis of aryl thiols is still yet to be reported. ...
Phenols and aryl thiols are fundamental building blocks in organic synthesis and final products with interesting biological activities. Over the past decades, substantial progress has been made in transition-metal-catalyzed coupling reactions, which resulted in the emergence of new methods for the synthesis of phenols and aryl thiols. Aryl halides have been extensively studied as substrates for the synthesis of phenols and aryl thiols. In very recent years, C–H activation represents a powerful strategy for the construction of functionalized phenols directly from various arenes. However, the synthesis of aryl thiols through C–H activation has not been reported. In this review, a brief overview is given of the recent advances in synthetic strategies for both phenols and aryl thiols.
... Transition-metal-catalyzed CÀHb ond functionalization reactions have become an essential method for the synthesis of functionalized organic compounds. [1,2] Although the use of noble metals,i ncluding Pd, Rh, Ru, and Ir,h as been dominating the field of C À Ha ctivation, [3] cobalt-catalyzed C À Hactivation reactions [4,5] have also received much interest because cobalt is earth-abundant and therefore less expensive than noble metals.M oreover,o wing to its unique reactivity and functional-group tolerance,the use of cobalt catalysts for C À Hactivation provides acomplementary method to noblemetal catalysis. ...
A highly diastereoselective method for the synthesis of dihydroepoxybenzofluorenone derivatives from aromatic/vinylic amides and bicyclic alkenes is described. This new transformation proceeds through cobalt-catalyzed C-H activation and intramolecular nucleophilic addition to the amide functional group. Transition-metal-catalyzed C-H activation reactions of secondary amides with alkenes usually lead to [4+2] or [4+1] annulation; to the best of our knowledge, this is the first time that a [3+2] cycloaddition is described in this context. The reaction proceeds under mild conditions and tolerates a wide range of functional groups. Mechanistic studies imply that the C-H bond cleavage may be the rate-limiting step.
... [1][2][3][4][5][6][7][8][9][10] Due to the importance and potential of CÀH activation reactions, many reviews exist to outline achievements in these organic syntheses. [11][12][13][14][15][16][17][18][19][20][21][22][23][24] In recent years, transition metal-catalyzed CÀH activation reactions have made significant advances in the synthesis of planar ammonium salts such as isoquinolinium, cinnolinium, quinolizinium, pyridinium, and other related salt compounds. These compounds are of great importance due to their presence in natural products and functional materials. ...
Cationic N-heterocycles are an important class of organic compounds largely present in natural and bioactive molecules. They are widely used as fluorescent dyes for biological studies, as well as in spectroscopic and microscopic methods. These compounds are key intermediates in many natural and pharmaceutical synthesis. They are also a potential candidate for organic light emitting diodes (OLEDs). Because of these useful applications, the development of new methods for the synthesis of cationic N-heterocycles has received a lot of attention. In particular, many C-H activation methodologies that realize high step- and atom-economies toward these compounds have been developed. In this review, recent advancements in the synthesis and applications of cationic N-heterocycles through C-H activation reactions are summarized. The new C-H activation reactions described in this review are preferred over their classical analogs.
... As an approach based on aromatic C-O bond formation, the intramolecular transition metal-catalyzed ipso substitution of aryl halide with an alcohol moiety was studied [9][10][11][12][13][14][15][16]. More recently, the oxidative aromatic C-O bond forming methods were developed [17]. Yu reported the oxidative approach to dihydrobenzofurans 2 from alcohols 1 via Pd(II)-catalyzed and hydroxyl-directed C-H bond activation followed by C-O bond formation [18]. ...
Most of the synthetic approaches to the benzo-fused heterocycles containing an oxygen atom have involved the use of phenol derivatives as a starting material. This review highlights the new synthetic approaches involving the aromatic C-O bond-forming process using arynes. The insertion of arynes into the C=O bond gives the unstable intermediates, [2 + 2] cycloaddition-type adducts, which can be easily converted into a variety of oxygen atom-containing heterocycles in a single operation. In this review, the syntheses of oxygen heterocycles, such as coumarin, chromene, xanthene, dihydrobenzofuran and benzofuran derivatives, via the insertion of arynes into the C=O bond of aldehydes or formamides are summarized.
... Some cross-dehydrogenative C-O coupling reactions are cursorily described in reviews on the oxidative C-heteroatom bond formation without the use of metal compounds [15], the Pd(II)catalyzed oxidative C-C, C-O, and C-N bond formation [3], the transition metal-catalyzed etherification of unactivated C-H bonds [19], the Pd(II)-catalyzed oxidative functionalization at the allylic position of alkenes [20,21], the oxidative functionalization catalyzed by copper compounds to form C-C, C-N, C-O, C-Hal, C-P, and N-N bonds [10], the Bu 4 NI/t-BuOOH oxidative system [22], selective functionalization of molecules [23], the oxidative esterification and oxidative amidation of aldehydes [24], and the transition metal-catalyzed radical oxidative cross-couplings [13]. The present review summarizes primary publications on the cross-dehydrogenative C-O coupling, with special emphasis on the studies published after 2000. ...
... Some cross-dehydrogenative C-O coupling reactions are cursorily described in reviews on the oxidative C-heteroatom bond formation without the use of metal compounds [15], the Pd(II)catalyzed oxidative C-C, C-O, and C-N bond formation [3], the transition metal-catalyzed etherification of unactivated C-H bonds [19], the Pd(II)-catalyzed oxidative functionalization at the allylic position of alkenes [20,21], the oxidative functionalization catalyzed by copper compounds to form C-C, C-N, C-O, C-Hal, C-P, and N-N bonds [10], the Bu 4 NI/t-BuOOH oxidative system [22], selective functionalization of molecules [23], the oxidative esterification and oxidative amidation of aldehydes [24], and the transition metal-catalyzed radical oxidative cross-couplings [13]. The present review summarizes primary publications on the cross-dehydrogenative C-O coupling, with special emphasis on the studies published after 2000. ...
The present review summarizes primary publications on the cross-dehydrogenative C–O coupling, with special emphasis on the studies published after 2000. The starting compound, which donates a carbon atom for the formation of a new C–O bond, is called the CH-reagent or the C-reagent, and the compound, an oxygen atom of which is involved in the new bond, is called the OH-reagent or the O-reagent. Alcohols and carboxylic acids are most commonly used as O-reagents; hydroxylamine derivatives, hydroperoxides, and sulfonic acids are employed less often. The cross-dehydrogenative C–O coupling reactions are carried out using different C-reagents, such as compounds containing directing functional groups (amide, heteroaromatic, oxime, and so on) and compounds with activated C–H bonds (aldehydes, alcohols, ketones, ethers, amines, amides, compounds containing the benzyl, allyl, or propargyl moiety). An analysis of the published data showed that the principles at the basis of a particular cross-dehydrogenative C–O coupling reaction are dictated mainly by the nature of the C-reagent. Hence, in the present review the data are classified according to the structures of C-reagents, and, in the second place, according to the type of oxidative systems. Besides the typical cross-dehydrogenative coupling reactions of CH- and OH-reagents, closely related C–H activation processes involving intermolecular C–O bond formation are discussed: acyloxylation reactions with ArI(O2CR)2 reagents and generation of O-reagents in situ from C-reagents (methylarenes, aldehydes, etc.).
2-Aryloxyquinolines are well known for various biological activities. In this report, we have developed a novel protocol for introducing an acetoxy functional group on the aryl sp² carbon of 2-aryloxyquinoline-3-carbaldehyde using a palladium catalyst for the first time. Interestingly, this C–H acetoxylation reaction is highly chemo- and site-selective. By modifying the reaction conditions, mono or di ortho-C–H acetoxylation products have been synthesized selectively with good yields and with good functional group tolerance.
