Default Latest Most Read Please wait a minute... Review Recent Advances on Transition-Metal-Catalyzed Halogenation of Unactivated C-H Bonds 2017 Awarded Liao Gang, Shi Bingfeng Acta Chimica Sinica 2015, 73 (12): 1283-1293. DOI: 10.6023/A15040295 Published: 15 September 2015 Abstract (1355) PDF (1386KB)(1651) Knowledge map Halogenation is one of the most important reactions in organic synthesis. Recently, transition-mental-catalyzed C-H halogenation has emerged as a powerful and economical strategy for the synthesis of organohalides. In this review, we summarize recent advances on transition-metal-catalyzed halogenation of unactivated C-H bonds, according to the types of transition metals(palladium, copper, rhodium, ruthenium, and cobalt), the scope of reactions and mechanism. Finally, the limitations and perspectives on C-H halogenation are also described. Reference | Related Articles | Metrics Cited: Baidu(12) CSCD(14) Editorial C—H Bond Functionalization: the Holy Grail of Chemistry 2017 Awarded Yu Jinquan, Ding Kuiling Acta Chimica Sinica 2015, 73 (12): 1223-1224. DOI: 10.6023/A1512E001 Published: 30 December 2015 Abstract (1309) PDF (668KB)(2441) Knowledge map Related Articles | Metrics Communication FeCl2-Catalyzed Oxidative Amidation of Aldehydes with Primary and Secondary Amines Li Yuanming, Jia Fan, Ma Lina, Li Zhiping Acta Chim. Sinica 2015, 73 (12): 1311-1314. DOI: 10.6023/A15040287 Published: 15 June 2015 Abstract (1295) PDF (381KB)(1461) Knowledge map The amidation reaction is an important process in both academia and industry for the synthesis of natural products, functional polymers, and pharmaceuticals. The development of new amidation methods for constructing such important class of organic compounds is still attracting considerable interests. We herein reported a general oxidative amidation of aldehydes with a variety of free primary or secondary amines using inexpensive iron(II) chloride as catalyst and tert-butyl hydroperoxide(TBHP) as oxidant. The present amidation reactions afford the corresponding secondary and tertiary amides in moderate to excellent yields. In addition, the amidations of benzimidazole and pyrazole were also achieved by the developed method. Reference | Supporting Info. | Related Articles | Metrics Review Recent Advances in Free-Radical-Promoted Selective Activation of Alcohol/Ether α-O-C(sp3)-H Bond 2017 Awarded Shang Xiaojie, Liu Zhongquan Acta Chimica Sinica 2015, 73 (12): 1275-1282. DOI: 10.6023/A15060407 Published: 12 October 2015 Abstract (1124) PDF (880KB)(1501) Knowledge map Alcohols/ethers are the most common chemicals. And the hydroxyl group in alcohols is believed to be universal functional group in synthetic organic chemistry. It is undeniably attractive to form a new chemical bond through selective cleavage of the α-O-C(sp3)-H bond. Considerable developments in the free-radical-promoted alcohol/ether C(sp3)-H functionalization have been achieved in recent years. These methods have drawn much attention from synthetic chemists due to the features of alcohol/ether as starting materials, reservation of the hydroxyl group and excellent regioselectivity, etc. This paper summarizes the recent advances in free-radical-initiated selective activation of the α-O-C(sp3)-H bonds in alcohol/ether. For a start, the possible factors such as bond dissociation energy(BDE) and stability of the key radical intermediate that dominates the regioselectivity in radical-initiated C(sp3)-H bond activation have been analyzed here. Moreover, recent developments in this field have been demonstrated in details from different reaction types as following.(a) Minisci reactions of heterocycles with alcohols/ethers;(b) Radical addition/elimination reactions of activated alkenes with alcohols/ethers;(c) Free-radical addition/cyclization cascade reactions of activated olefins and/or biaryl isonitriles with alcohols/ethers;(d) Free-radical addition/difunctionalization and rearrangement reactions of alcohols/ethers with activated alkenes. Besides, other free radical reactions such as oxidative coupling reactions of aryl boronic acids with ethers, C-O and C-N bond formation reactions have also been exhibited. In addition, the suggested mechanisms for most of these reactions have been depicted and discussed in this review. Finally, the disadvantages of present systems and the possible modifications along with the future studies of this active area have been summarized at the end of this article. Reference | Related Articles | Metrics Communication Palladium-Catalyzed Trifluoromethylthiolation of Arenes via C-H Activation 2017 Awarded Xu Jiabin, Chen Pinhong, Ye Jinxing, Liu Guosheng Acta Chimica Sinica 2015, 73 (12): 1294-1297. DOI: 10.6023/A15030211 Published: 15 May 2015 Abstract (1104) PDF (449KB)(1208) Knowledge map Fluorinated organic compounds are widely used as pharmaceuticals, agrochemicals and materials. Among them, the trifluoromethylthio(-SCF3) compounds has attracted much attention owning to its strong electron-withdrawing nature and high lipophilicity. Therefore, the development of new trifluoromethylthiolation methods has attracted great interest in synthetic organic chemistry. Traditional approaches for the synthesis of trifluoromethylthiolated arenes include halogen-fluorine exchange and the trifluoromethylation of sulfur-containing compounds such as disulfides, thiols, which suffer from poor functional compatibility and yield. Recent progress on the transition metal-catalyzed directing trifluoromethylthiolation using SCF3 reagents provided an efficient approach to the target. Herein, we reported a Pd(II)-catalyzed highly selective C-H trifluoromethylthiolation of arenes. Different type of pyridines could be used as efficient directing groups for this reaction. In this reaction, benzoyl chloride was found to be crucial to activate the trifluoromethanesulfanamide 2a. It provides an efficient way for the synthesis of ortho-SCF3 substituted arenes in high yields. A representative procedure for this reaction is as following:To a 10 mL glass tube, Pd(OAc)2(4.4 mg, 0.02 mmol), AgOAc(33 mg, 0.2 mmol), PhNHSCF3(50μL, 0.5 mmol), substrate(0.2 mmol) and PhCOCl(58μL, 0.5 mmol) were dissolved in dry DMF(1 mL) under N2 atmosphere. The tube was sealed and the mixture was stirred at 120℃ for 12 h, and then cooled to room temperature. The mixture was concentrated and purified by column chromatography on silica gel with a gradient eluent of petroleum ether and ethyl acetate(range from 15:1 to 4:1) to provide the products in 62%~91% yields. Reference | Supporting Info. | Related Articles | Metrics Cited: CSCD(10) Highlight Recent Development in Pd-Catalyzed meta-C(sp2)-H Bond Activation Based on Directing Strategy Yuan Yizhi, Song Song, Jiao Ning Acta Chim. Sinica 2015, 73 (12): 1231-1234. DOI: 10.6023/A15050319 Published: 29 June 2015 Abstract (962) PDF (814KB)(1394) Knowledge map In recent years, remarkable progress has been achieved in Pd-catalyzed meta-C(sp2)-H bond activation with directing groups. Based on remote activation strategy, a series of U-shaped directing groups have been devised by Yu and others and have been utilized in the olefination, arylation and acetoxylation of different types of substrates with the assistance of mono-protected amino acids(MPAA). Very recently, Yu reported the Pd-catalyzed meta-C(sp2)-H bond activation via the tandem reaction of ortho-C(sp2)-H bond activation and Catellani reaction using simple directing groups, in which alkylation and arylation could all be realized under the Pd/norbornene catalytic system. Dong and co-workers developed arylation of the meta-C(sp2)-H bond of N,N-dimethylbenzylamine with similar strategy. It is noteworthy that these above mentioned meta-C(sp2)-H bond activation protocols could be applied in the late-stage modification and the synthesis of some biologically active molecules and pharmaceutical intermediates. This manuscript will highlight the latest advances in Pd-catalyzed meta-C(sp2)-H bond activation with directing groups. Reference | Related Articles | Metrics Review Selective Functionalization of Normal Alkyl C-H Bonds Using Amides as Directing Groups Zhou Lihong, Lu Wenjun Acta Chim. Sinica 2015, 73 (12): 1250-1274. DOI: 10.6023/A15040278 Published: 15 June 2015 Abstract (908) PDF (1493KB)(1152) Knowledge map Normal alkyl C-H bonds refer to those sp3 C-H bonds not linking with any carbon functional groups or hetero-atoms at their adjacent positions. They are fundamental chemical bonds, which are widespread both in raw materials such as petroleum oil, natural gas etc. for chemical industries and in various kinds of intermediates for chemical syntheses. Selective transformation of these ubiquitous alkyl C-H bonds into new carbon-carbon, carbon-nitrogen, or carbon-oxygen bonds is an ideal method in construction of molecular skeletons, extension of carbon-chains and introduction of functional groups, which is urgently desired in either large-scale production or laboratory synthesis. However, these normal sp3 C-H bonds are extremely chemical inert, due to their high bond dissociation energy and low acid dissociation constant. Thus, they are not used directly and conveniently as other available functional groups in synthetic chemistry. Since the beginning of this century, the functionalization of normal alkyl C-H bonds has been developed rapidly through C-H activation which is to cleave these inert C-H bonds with the assistance of some special directing groups by use of catalytic transition-metal complexes under mild conditions. Amides as one of the effective directing groups, which are prevalent in natural products and pharmaceuticals, has also received particular attention. A series of novel reactions using various amides as directing groups to produce carbon-carbon and carbon-heteroatom bonds, including alkyl-aryl, alkyl-alkenyl, alkyl-carbonyl, alkyl-alkynyl, alkyl-alkyl linkages and carbon-nitrogen, carbon-oxygen, carbon-chlorine, carbon-bromine, carbon-boron, carbon-sulfur, carbon-selenium bonds, etc. have been established, and some of them have been applied to the practical synthesis already. This review describes the development on the functionalization of normal alkyl C-H bonds according to the formed bonds, reaction substrates, and chronological order. It is emphasized that the structures of amide groups, properties of transition metals, regional and stereo-selectivities in C-H activations, reaction mechanisms, subsequent transformations and their synthetic applications, etc. Reference | Related Articles | Metrics Cited: Baidu(1) CSCD(6) Highlight Recent Advances in Directed Intramolecular C(sp3)-H Amination Reactions for the Construction of Aza-heterocycles 2017 Awarded Zhao Jinbo, Zhang Qian Acta Chim. Sinica 2015, 73 (12): 1235-1244. DOI: 10.6023/A15010063 Published: 04 March 2015 Abstract (842) PDF (908KB)(1190) Knowledge map Saturated N-heterocycles, such as β-lactam, aziridine, pyrrolidine, piperidine and their benzo-structures indoline, tetrahydroquinoline and tetrahydroisoquinoline, are important "privileged scaffolds" which are of pivotal importance to medicinal chemistry. Intramolecular C-H bond amination reaction has emerged as a straightforward and atom-economical alternative for the synthesis of N-heterocycles. Among the existing C-H amination methodologies, the directed C(sp3)-H amination processes manifested unique reactivity and complementary selectivity profiles in comparison to those of the established methods such as Hoffman-Löffler-Freytag reaction and metal nitrenoid chemistry. These features render directed C(sp3)-H amination an appealing and powerful addition to the amination toolbox available to synthetic chemists. Although this field is still in its infancy, its development has already uncovered fundamental understanding of the reactivity and selectivity patterns of various types of C(sp3)-H bonds, upon which its synthetic applicability was elegantly demonstrated through the synthesis of several natural and artificial chemical entities of high therapeutic relevance. Highlighted herein is the recent important developments in the directing group enabled intramolecular C(sp3)-H amination strategies to construct N-heterocycles, with an emphasis on substrate scope and limitation, selectivity and synthetic applications. The reactions are classified based on the types of directing groups employed. The employment of chelating directing groups compensates entropy loss during catalyst-substrate interaction and enables successful activation of unactivated C(sp3)-H bonds and facile access to azetidines, β-lactams and pyrrolidines via the intermediacy of 5/5 and 5/6 bicyclic metallacycles. Besides palladium catalyst, copper and nickel salts have also been reported to realize similar processes with unique selectivities. Notably, amide directed C(sp3)-H amidation reaction under a novel AgI/AgⅢ redox catalysis furnished the pyrrolidine scaffold via 6-membered metallacycle. It was applied in the efficient construction of the core structures of natural products(-)-codonopsinine and(-)-Martinellic acid in one operation. The use of innate functionality in the substrate as directing group obviates extra installation and removal steps required for C-H activation reactions. Toward this end, catalytic carbonylation and aziridination reactions were developed via the intermediacy of a novel strained 4-membered palladacycle to afford strained aziridines and β-lactams through PdII/PdIV and Pd0/PdII redox pathways, respectively. Taken together, the above developments have opened new avenues toward more efficient and atom-economic synthesis of important N-heterocycles. Reference | Related Articles | Metrics Highlight Autoxidative Coupling and Its Applications to C-H Functionalization Lu Qingquan, Yi Hong, Lei Aiwen Acta Chim. Sinica 2015, 73 (12): 1245-1249. DOI: 10.6023/A14120888 Published: 04 March 2015 Abstract (793) PDF (746KB)(1091) Knowledge map As a highly economic and efficient strategy for chemical bond formation, oxidative coupling has been widely applied in synthetic organic chemistry. Recently, Klussmann, Jiao and Huo et al. groups have successfully achieved the direct functionalization of Csp3-H and Csp2-H bonds through developing simple, elegant autoxidative coupling reactions, which makes a significant progress in this filed. This highlight mainly reviews the recent advances in autoxidative coupling. Reference | Related Articles | Metrics Cited: Baidu(1) CSCD(7) Communication Visible-Light Photoredox Catalysis:Direct Arylation of Elec-tron-Deficient Heterocycles and Arenes with Aryl Diazonium Salts Zuo Xuan, Wu Wenliang, Su Weiping Acta Chim. Sinica 2015, 73 (12): 1298-1301. DOI: 10.6023/A15040284 Published: 30 December 2015 Abstract (792) PDF (375KB)(877) Knowledge map Visible-light-mediated Ru(bpy)3(PF6)2 catalyzed arylation of electron-deficient heteroarenes with aryl diazonium salts has been achieved under mild conditions, and a series of benzene derivatives can also be arylated under similar reaction conditions in moderate to good yields. Reference | Supporting Info. | Related Articles | Metrics Cited: CSCD(3) Communication Copper-Promoted Oxidative C-H Bond Amination of Hydrazones:Synthesis of 1H-Indazoles and 1H-Pyrazoles Ding Zhengwei, Tan Qitao, Liu Bingxin, Zhang Kea, Xu Bin Acta Chim. Sinica 2015, 73 (12): 1302-1306. DOI: 10.6023/A15040263 Published: 15 June 2015 Abstract (724) PDF (489KB)(850) Knowledge map An efficient copper-promoted C(sp2)-H bond amination was developed to afford 1H-indazoles and 1H-pyrazoles in moderate to excellent yields from easily accessible hydrazones. This process tolerated a variety of functional groups and afforded the corresponding 1H-indazoles and 1H-pyrazoles under mild conditions. Reference | Supporting Info. | Related Articles | Metrics Communication Rh/Ag Bimetallic Catalyzed C-H Bond Olefination of Benzonitriles Lu Ping, Feng Chao, Loh Teck-Peng Acta Chim. Sinica 2015, 73 (12): 1315-1319. DOI: 10.6023/A15050322 Published: 15 June 2015 Abstract (608) PDF (507KB)(921) Knowledge map Transition-metal-catalyzed C-H functionalization emerges as an atom-economical and highly efficient strategy in the synthetic organic chemistry. In this regard, oxidative Heck reaction, pioneered by Fujiwara and Moritani, represents a great evolvement to the traditional Heck reaction by obviating the substrate preactivation. While palladium was routinely adopted as the catalyst of choice because of its well established catalytic activities, other transition metals, especially rhodium also proved to be suitable candidate in pursuit of such oxidative C-H alkenylation because of its low catalyst loading, high efficiency and function group tolerance. Under such circumstance, the Rh(Ⅲ)-catalyzed oxidative C-H alkenylation has witness a great advancement in the past decade, with many functionalities such as-COOH,-CONHR, CO2Et, NHAc etc. being explored as suitable directing groups for the initiation of C-H activation. However, most of these directing groups needed prior installation. With our continuing interest in Rh(Ⅲ)-catalyzed C-H functionalization, herein we would like to present a nitrile based bimetallic Rh/Ag catalyzed C-H alkenylation reaction. In this protocol, nitrile was assumed to transform into imine which then took part into the Rh(Ⅲ) catalyzed C-H bond olefination reation. With such reaction cascade, a library of ortho-alkenylated benzamides could be directly obtained from benzonitriles in one pot fashion. All the substrates are commercially available and easy to obtain. A general procedure for the bimetallic Rh/Ag catalyzed C-H olefination of benzonitriles:an oven-dried 10 mL Schlenk tube was charged with nitrile 1(If the nitrile was solid, 0.2 mmol),[RhCp*Cl2]2(6.2 mg, 0.01 mmol), AgSbF6(13.8 mg, 0.04 mmol) in sequence, followed by refilling with N2. Then olefins 2(0.5 mmol), nitriles 1(If the nitrile was liquid, 0.2 mmol) and AcOH were added through syringe. After stirring at 120℃ for 24 h, the reaction mixture was cooled to room temperature and filtered through a celite plug. The solvent was removed in vacuo and the residue was purified by column chromatography to afford the desired product 3. Reference | Supporting Info. | Related Articles | Metrics Cited: CSCD(2) Communication Synthesis and Reactivity of Cobalt Pincer Complexes Formed by Carbon-Hydrogen Bond Activation Zhao Hua, Sun Hongjian, Wang Lin, Li Xiaoyan Acta Chim. Sinica 2015, 73 (12): 1307-1310. DOI: 10.6023/A15030190 Published: 25 May 2015 Abstract (506) PDF (965KB)(500) Knowledge map By treating diphosphinito[PCP]-pincer ligand,(Ph2P(ortho-C6H4))2CH2(1) with CoMe(PMe3)4 or CoMe3(PMe3)3 the same Csp3-H bond activation product[PCP]Co(I)(PMe3)(2) was obtained at room temperature. Treatment of 2 with C6Cl6, EtBr or n-BuBr and CH3I gave rise to the single electron oxidation addition products[PCP]Co(II)X(PMe3)[X=Cl(3), Br(4) and I(5)]. The molecular structures of 2~6 were confirmed by X-ray diffraction analysis. Reference | Supporting Info. | Related Articles | Metrics