- Chromium-Catalyzed Selective Cross-Electrophile Coupling between Unactivated C(aryl)-F and C(aryl)-O Bonds
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Chemically inert C(aryl)-F bonds have rarely been used to couple with other unactivated bonds, and this remains a challenge because of the difficulty of the successive cleavage of two unactivated bonds by metal catalysis. We report here the chromium-catalyzed cleavage of chemically inert C(aryl)-F bonds for coupling with unactivated C(aryl)-O bonds, allowing cross-electrophile coupling between unreactive aryl fluorides and aryl esters to be achieved in high regio- and chemoselectivity. The reactive Cr, which was formed in situ by reducing CrCl2, enables cleavage of the o-C(aryl)-F bonds to afford monovalent and quartet cyclochromate; subsequent bipyridyl-enabled insertion into the ester C(aryl)-O bond followed by reductive elimination allowed the orthogonal coupling of these two different and unactivated bonds. Mechanistic studies indicate that the bipyridyl ligand greatly enhances the reactivity of Cr in the cleavage of C(aryl)-O bonds, and the second oxidative addition may occur sluggishly compared with the reductive elimination in the catalytic cycle.
- Fan, Fei,Zhao, Lixing,Luo, Meiming,Zeng, Xiaoming
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supporting information
p. 561 - 568
(2022/03/15)
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- Reductive Cross-Coupling between Unactivated C(aryl)-N and C(aryl)-O Bonds by Chromium Catalysis Using a Bipyridyl Ligand
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Reductive cross-coupling between two chemically inert bonds remains a great challenge in synthetic chemistry. We report here the reductive cross-coupling between unactivated C(aryl)-N and C(aryl)-O bonds that was achieved by chromium catalysis. The simple and inexpensive CrCl2 salt, combined with important bipyridyl ligand and magnesium reductant, shows high reactivity in the successive cleavage of C(aryl)-N bonds of aniline derivatives and C(aryl)-O bonds of aryl esters, allowing the cross-coupling of these two unactivated and different bonds to occur in a reductive fashion to form a C(aryl)-C(aryl) bond. Mechanistic studies by deuterium-labeling experiments indicate that the C(aryl)-N bonds in anilines are preferentially cleaved by reactive Cr species, in which the ligation of bipyridyl with Cr by adopting a coordination model in 1:1 ratio can be considered.
- Cong, Xuefeng,Fan, Fei,Luo, Meiming,Tang, Jinghua,Zeng, Xiaoming,Zhao, Lixing
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p. 12834 - 12840
(2020/08/21)
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- Chemoselective Cross-Coupling between Two Different and Unactivated C(aryl)-O Bonds Enabled by Chromium Catalysis
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We report here the first example of cross-coupling between two different and unactivated C(aryl)-O bonds with chromium catalysis. The combination of a low-cost Cr(II) salt, 4,4′-di-tert-butyl-2,2′-dipyridyl (dtbpy) as the ligand, and magnesium as the reductant shows high reactivity in promoting the reductive cross-coupling of aryl methyl ether derivatives with aryl esters by cleavage and coupling of two different C(aryl)-O bonds under mild conditions. The formation of active low-valent Cr species by reduction of CrCl2 with Mg can be considered, which prefers to initially activate the C(aryl)-O bond of phenyl methyl ether with the chelation help of dtbpy and an o-imine auxiliary. The subsequent consecutive reduction, second C(aryl)-O activation, and reductive elimination allow for the achievement of selective cross-coupling of C(aryl)-O/C(aryl)-O bonds.
- Tang, Jinghua,Liu, Liu Leo,Yang, Shangru,Cong, Xuefeng,Luo, Meiming,Zeng, Xiaoming
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supporting information
p. 7715 - 7720
(2020/05/20)
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- Catalytic Asymmetric Radical-Polar Crossover Hydroalkoxylation
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Asymmetric intramolecular hydrofunctionalization of tertiary allylic alcohols is described. This metal hydride-mediated catalytic radical-polar crossover reaction delivers corresponding epoxides in good to high enantioselectivity and constitutes the first example of asymmetric hydrogen atom transfer-initiated process. A series of modified cobalt salen complexes has proven optimal for achieving good efficiency and asymmetric induction. Experimental data suggest that cationic cobalt complexes may be involved in the enantiodetermining step, where cation-πinteractions in the catalyst contribute to the asymmetric induction.
- Discolo, Christopher A.,Touney, Eric E.,Pronin, Sergey V.
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supporting information
p. 17527 - 17532
(2019/11/05)
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- COMPOUNDS OF PHOSPHINANES AND AZAPHOSPHINANES, A PROCESS FOR THEIR PREPARATION AND PHARMACEUTICAL COMPOSITIONS CONTAINING THEM
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Compounds of formula (I) wherein: Ak1 represents an alkyl chain, X represents —(CH2)m—, —CH(R)—, —N(R)—, —CH2—N(R)—, —N(R)—CH2— or —CH2—N(R)—CH2—, m and R are as defined in the description, R1 and R2 each represent H when X represents —(CH2)m—, —CH(R)—, —N(R)—, —CH2—N(R)— or —N(R)—CH2—, or together form a bond when X represents —CH2—N(R)—CH2—, R3 represents NH2, Cy-NH2, Cy-Ak3-NH2 or piperidin-4-yl, Cy and Ak3 are as defined in the description, R4 and R5, which may be identical or different, each represent H or F, their optical isomers, and addition salts thereof with a pharmaceutically acceptable acid. Medicinal products containing the same which are useful in treating conditions requiring a TAFIa inhibitor.
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Paragraph 0314; 0380; 0381; 0382
(2018/02/27)
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- Chromium-Catalyzed, Regioselective Cross-Coupling of C-O Bonds by Using Organic Bromides as Reactants
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We report a chromium-catalyzed cross-coupling of C-O bonds with widely accessible organic bromides as reactants for the preparation of ortho -arylated or -alkylated aromatic aldehydes at room temperature. The use of metallic magnesium is essential for the reaction to occur, giving it an advantage over previous reactions involving Grignard reagents that have to be prepared separately from organic halides before the coupling.
- Tang, Jinghua,Luo, Meiming,Zeng, Xiaoming
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supporting information
p. 2577 - 2580
(2017/09/28)
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- (Biphenyl-2-alkyne) derivatives as common precursors for the synthesis of 9-iodo-10-organochalcogen-phenanthrenes and 9-organochalcogen-phenanthrenes
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In this paper, we report our results on the cyclization of (biphenyl-2-alkyne) derivatives to give two different types of phenanthrene derivatives, 9-iodo-10-organochalcogen-phenanthrenes and 9-organochalcogen-phenanthrenes. The strategy for the synthesis was based on the use of electrophilic cyclization for the preparation of 9-iodo-10-organochalcogen-phenanthrenes and iron(iii) chloride/diorganyl diselenide-mediated intramolecular cyclization to prepare 9-organochalcogen-phenanthrenes. The effects of solvent, temperature, reaction time and stoichiometry on the efficiency of cyclization reactions were investigated. The standard reaction conditions were compatible with many functional groups in the substrates, such as methyl, chlorine, fluorine and methoxyl. This protocol was efficient for diorganyl diselenides and disulfides but ineffective for diorganyl ditellurides. The resulting phenanthrenes were further functionalized through Sonogashira reactions followed by the electrophilic cyclization reaction to give the selenophene-fused aromatic compounds.
- Grimaldi, Tamiris B.,Lutz, Guilherme,Back, Davi F.,Zeni, Gilson
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p. 10415 - 10426
(2016/11/18)
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- Formation of a carbonyl group ortho to a biaryl structure or a 6H-dibenzopyran by a palladium/norbornene-catalyzed ordered reaction sequence
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Abstract Developments are reported in the catalytic synthesis of biaryls containing an ortho-carbaldehyde or 6H-dibenzopyrans in the presence of palladium/norbornene as catalyst. The reaction of o-substituted aryl iodides and o-bromobenzyl alcohols proceeds by unsymmetrical aryl-aryl coupling to form a seven-membered oxapalladacycle intermediate, which may undergo an intramolecular redox process to form carbonyl groups or a C-O coupling to six-membered cyclic ethers. The predominant formation of dibenzopyrans as well as of biaryl structures containing the oxidized CHO group in one ring and the reduced CH2OH in the other is described along with some mechanistic insights.
- Della Ca, Nicola,Fontana, Marco,Xu, Di,Cremaschi, Mirko,Lucentini, Riccardo,Zhou, Zhi-Ming,Catellani, Marta,Motti, Elena
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p. 6389 - 6401
(2015/08/18)
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- Regio- and Chemoselective Kumada-Tamao-Corriu Reaction of Aryl Alkyl Ethers Catalyzed by Chromium under Mild Conditions
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Acting as an environmentally benign synthetic tool, the cross-coupling reactions with aryl ethers via C-O bond activation have attracted broad interest. However, the functionalizations of C-O bonds are mainly limited to nickel catalysis, and selectivity has long been a prominent challenge when several C-O bonds are present in the one molecule. We report here the first chromium-catalyzed selective cross-coupling reactions of aryl ethers with Grignard reagents by the cleavage of C-O(alkyl) bonds. Diverse transformations were achieved using simple, inexpensive chromium(II) precatalyst combining imino auxiliary at room temperature. It offers a new avenue for buildup functionalized aromatic aldehydes with high efficiency and selectivity.
- Cong, Xuefeng,Tang, Huarong,Zeng, Xiaoming
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supporting information
p. 14367 - 14372
(2015/12/01)
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- Pinpoint-fluorinated phenacenes: New synthesis and solubility enhancement strategies
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The Pd(II)-catalyzed cyclizations of 2,2-difluorovinylated biaryls, following a Friedel-Crafts-type mechanism, provide a new route to pinpoint-fluorinated phenacenes. The single fluorine substituent stabilized the synthesized fluoropicenes (fluoro[5]phenacenes) toward aerial oxidation and contributed to their solubility in organic solvents. For example, 6- and 13-fluoropicenes were 25- and 15-fold more soluble in THF than nonfluorinated picene. X-ray crystal structure analysis revealed that the fluorine substituent did not alter molecular planarity.
- Fuchibe, Kohei,Morikawa, Toshiyuki,Shigeno, Kento,Fujita, Takeshi,Ichikawa, Junji
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p. 1126 - 1129
(2015/03/14)
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- A new synthetic approach to 6-unsubstituted phenanthridine and phenanthridine-like compounds under mild and metal-free conditions
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A new and mild synthetic approach for the synthesis of 6-unsubstituted phenanthridine and phenanthridine-like compounds under metal-free conditions at room temperature has been developed. The strategy involved a tandem azide rearrangement/intramolecular annulation and oxidation reactions of biarylmethyl azide precursors to obtain the desired products in up to 99% yields with high regioselectivity.
- Tummatorn, Jumreang,Krajangsri, Suppachai,Norseeda, Krissada,Thongsornkleeb, Charnsak,Ruchirawat, Somsak
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supporting information
p. 5077 - 5081
(2014/07/08)
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- Gold-catalyzed 6-exo-dig cycloisomerization: A versatile approach to functionalized phenanthrenes
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A novel gold-catalyzed 6-exo-dig cycloisomerization of o-propargylbiaryls has been developed that provides ready access to functionalized phenanthrenes in largely good to excellent yields. Notable features of this method are readily available starting materials, mild reaction conditions, and broad substrate scope. Golden cat: A novel gold-catalyzed 6-exo-dig cycloisomerization of o-propargylbiaryls has been developed that provides ready access to functionalized phenanthrenes in largely good to excellent yields. Notable features of this method are readily available starting materials, mild reaction conditions, and broad substrate scope.
- Shu, Chao,Li, Long,Chen, Cheng-Bin,Shen, Hong-Cheng,Ye, Long-Wu
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supporting information
p. 1525 - 1529
(2014/06/09)
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- Atom-economic threefold cross-couplings of triarylbismuth reagents with 2-halobenzaldehydes and pot-economic in situ Wittig functionalizations with phosphonium salts
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In this paper we report an efficient pot-economic methodology for the synthesis of ortho-olefinated biaryls. This has been achieved through an atom-economic threefold cross-coupling of triarylbismuth reagents with 2-halobenzaldehydes followed by pot-economic in situ Wittig olefination. The overall process is a pot-economic straightforward synthesis of ortho-olefinated biaryls from 2-halobenzaldehydes, triarylbismuth reagents and phosphonium salts. This pot-economic approach was applied to the formal synthesis of medicinally important Eupomatilone-6.
- Rao, Maddali L. N.,Dhanorkar, Ritesh J.
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p. 63792 - 63806
(2015/02/19)
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- Bismuth-catalyzed synthesis of polycyclic aromatic hydrocarbons (PAHs) with a phenanthrene backbone via cyclization and aromatization of 2-(2-arylphenyl)vinyl ethers
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The reaction of 2-(2-arylphenyl)vinyl ethers in the presence of a catalytic amount of bismuth(III) triflate gave substituted phenanthrenes in excellent yields under mild reaction conditions. The reaction was also applied to the construction of other polycyclic aromatic hydrocarbons (PAHs), such as chrysene, helicene, and pyrene having a phenanthrene backbone, via regioselective cyclization. This method has the advantages of easy availability of the cyclization precursors, operational simplicity, and high reaction efficiency.
- Murai, Masahito,Hosokawa, Naoki,Roy, David,Takai, Kazuhiko
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p. 4134 - 4137
(2014/09/30)
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- A sequential Pd/norbornene-catalyzed process generates o- biaryl carbaldehydes or ketones via a redox reaction or 6 h -dibenzopyrans by C-O ring closure
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o-Biaryl carbaldeydes and ketones are obtained through the one-pot reaction of o-aryl iodides with o-bromobenzyl alcohols under the catalytic action of Pd and norbornene, in the presence of a base. The same reaction can also give dibenzopyrans by Pd and norbornene catalysis with a different termination, leading to C-O ring closure. In both cases the process first leads to a five-membered palladacycle, which controls C-C coupling, then to a seven-membered oxapalladacycle, which gives aldehydes and ketones or dibenzopyrans.
- Motti, Elena,Ca, Nicola Della,Xu, Di,Piersimoni, Anna,Bedogni, Elena,Zhou, Zhi-Ming,Catellani, Marta
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supporting information
p. 5792 - 5795
(2013/01/15)
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- NOVEL CURCUMIN DERIVATIVE
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To develop a highly safe measure to treat Alzheimer's disease using a secretase-inhibiting substance, there is provided a compound represented by the following general formula (I) or a salt thereof: wherein A represents a phenyl group or the like, R1 represents a chlorine atom, a bromine atom, or a nitro group or the like, R2, R3, R4, and R5 each represent a hydrogen atom or the like, and L represents CH2—CH2 or CH═CH.
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Page/Page column 13
(2011/04/24)
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- NOVEL CURCUMIN DERIVATIVE
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The present invention provides a novel compound that is structurally similar to curcumin and has a suppressive effect on Aβ aggregation, a degradative effect on Aβ aggregates, an inhibitory effect on β-secretase, and a protective effect on neurons. The novel compound is a compound represented by the following general formula (Ia) or a salt thereof: wherein R1 represents a 4-hydroxy-3-methoxyphenyl group or the like, and R2 represents a 1H-indol-6-yl group or the like.
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Page/Page column 110
(2009/12/07)
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- An aryl to imidoyl palladium migration process involving intramolecular C-H activation
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Biologically interesting fluoren-9-one and xanthen-9-one derivatives have been prepared by a novel aryl to imidoyl palladium migration, followed by intramolecular arylation. The fluoren-9-one synthesis appears to involve both a palladium migration mechanism and a C-H activation process proceeding through an unprecedented organopalladium(IV) hydride intermediate. The results from deuterium labeling experiments are consistent with the proposed dual mechanism.
- Zhao, Jian,Yue, Dawei,Campo, Marino A.,Larock, Richard C.
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p. 5288 - 5295
(2008/02/02)
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