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41.
Dr. He Zhao Xiu Li Rongqing Guan Prof. Huanfeng Jiang Prof. Min Zhang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(69):15858-15862
The tandem dual C−H amination of tetrahydroquinoxalines with free amines under aerobic copper catalysis conditions has been demonstrated. The synthetic protocol proceeds with good substrate and functional group compatibility, mild reaction conditions, short reaction time, the use of the naturally abundant [Cu]/O2 catalyst system, excellent chemoselectivity and synthetic efficiency, and with no need for the pre-installation of specific aminating agents, which offers a practical platform for the rapid and diverse synthesis of diaminoquinoxalines. Moreover, this work has shown the potential of single-electron-oxidation-induced C−H functionalization of N-heterocycles, and its application in the development of optoelectronic materials. 相似文献
42.
Friedrich Kreyenschmidt Selim E. Meurer Prof. Dr. Konrad Koszinowski 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(23):5912-5921
>The combination of CoCl2 with bidentate phosphines is known to catalyze challenging cross-coupling and Heck-type reactions, but the mechanisms of these valuable transformations have not been established. Here, we use electrospray-ionization mass spectrometry to intercept the species formed in these reactions. Our results indicate that a sequence of transmetalation, reductive elimination, and redox disproportionation convert the cobalt(II) precatalyst into low-valent cobalt complexes. These species readily transfer single electrons to alkyl bromides, which thereupon dissociate into alkyl radicals and Br−. In cross-coupling reactions, the alkyl radicals add to the cobalt catalyst to form observable heteroleptic complexes, which release the coupling products through reductive eliminations. In the Heck-type reactions, the low abundance of newly formed ionic species renders the analysis more difficult. Nonetheless, our results also point to the occurrence of single-electron transfer processes and the involvement of radicals in these transformations. 相似文献
43.
Christopher Lombardi Dr. Richard P. Rucker Dr. Robert D. J. Froese Dr. Sepideh Sharif Prof. Pier Alexandre Champagne Prof. Michael G. Organ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(62):14223-14229
The relative rates of arylation of primary alkylamines with different Pd-NHC catalysts have been measured, as have the relative rates of arylation of the secondary aniline product in an attempt to understand the key ligand design features necessary to have high selectivity for the monoarylated amine product. As the substituents on the N-aryl ring of the NHC increase in size, selectivity for monoarylation increases and this is further enhanced by chlorinating the back of the NHC ring. Computations have been performed on the catalytic cycle of this transformation in order to understand the selectivity obtained with the different catalysts. 相似文献
44.
In Situ Generation of ArCu from CuF2 Makes Coupling of Bulky Aryl Silanes Feasible and Highly Efficient
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Juan delPozo Prof. Juan A. Casares Prof. Pablo Espinet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(12):4274-4284
A bimetallic system of Pd/CuF2, catalytic in Pd and stoichiometric in Cu, is very efficient and selective for the coupling of fairly hindered aryl silanes with aryl, anisyl, phenylaldehyde, p‐cyanophenyl, p‐nitrophenyl, or pyridyl iodides of conventional size. The reaction involves the activation of the silane by CuII, followed by disproportionation and transmetalation from the CuI(aryl) to PdII, upon which coupling takes place. CuIII formed during disproportionation is reduced to CuI(aryl) by excess aryl silane, so that the CuF2 system is fully converted into CuI(aryl) and used in the coupling. Moreover, no extra source of fluoride is needed. Interesting size selectivity towards coupling is found in competitive reactions of hindered aryl silanes. Easily accessible [PdCl2(IDM)(AsPh3)] (IDM = 1,3‐dimethylimidazol‐2‐ylidene) is by far the best catalyst, and the isolated products are essentially free from As or Pd (<1 ppm). The mechanistic aspects of the process have been experimentally examined and discussed. 相似文献
45.
Philip Eckert Prof. Michael G. Organ 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(35):e202200665
Bulky Pd−N-heterocyclic carbene (NHC) catalysts (e. g., N-(di-2,6-(3-pentyl)phenyl), IPent) have been shown to have significantly higher reactivity in a wide variety of cross-coupling applications (i. e., C−C, C−S, C−N) than less hindered variants (e. g., N-(di-2,6-(isopropyl)phenyl), IPr). Further, chlorinating the backbone of the NHC ring sees an even greater increase in reactivity. In the cross-coupling of (hetero)aryl electrophiles to secondary alkyl nucleophiles, making the N-aryl groups larger reduces the amount of β-hydride elimination leading to alkene byproducts and chlorinating the NHC core had an even greater effect, all but eliminating alkene formation. In the present study involving the cross-coupling of primary alkyl electrophiles and nucleophiles, a sharp and surprising reversal of all of the above trends was observed. Bulkier catalysts had generally slower rate of reaction and β-hydride elimination worsened leading to extensive amounts of alkene byproducts. 相似文献
46.
Dr. Laura Ielo Prof. Dr. Vittorio Pace Prof. Dr. Wolfgang Holzer Md. Mahbubur Rahman Dr. Guangrong Meng Dr. Roman Szostak Prof. Dr. Michal Szostak 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(69):16246-16250
The structure and properties of amides are of tremendous interest in organic synthesis and biochemistry. Traditional amides are planar and the carbonyl group non-electrophilic due to nN→π*C=O conjugation. In this study, we report electrophilicity scale by exploiting 17O NMR and 15N NMR chemical shifts of acyclic twisted and destabilized acyclic amides that have recently received major attention as precursors in N-C(O) cross-coupling by selective oxidative addition as well as precursors in electrophilic activation of N-C(O) bonds. Most crucially, we demonstrate that acyclic twisted amides feature electrophilicity of the carbonyl group that ranges between that of acid anhydrides and acid chlorides. Furthermore, a wide range of electrophilic amides is possible with gradually varying carbonyl electrophilicity by steric and electronic tuning of amide bond properties. Overall, the study quantifies for the first time that steric and electronic destabilization of the amide bond in common acyclic amides renders the amide bond as electrophilic as acid anhydrides and chlorides. These findings should have major implications on the fundamental properties of amide bonds. 相似文献
47.
Guillaume Erbland Dr. Seifallah Abid Yohan Gisbert Nathalie Saffon-Merceron Yuichiro Hashimoto Leonardo Andreoni Théo Guérin Dr. Claire Kammerer Prof. Dr. Gwénaël Rapenne 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(71):16328-16339
The design and synthesis of two families of molecular-gear prototypes is reported, with the aim of assembling them into trains of gears on a surface and ultimately achieving controlled intermolecular gearing motion. These piano-stool ruthenium complexes incorporate a hydrotris(indazolyl)borate moiety as tripodal rotation axle and a pentaarylcyclopentadienyl ligand as star-shaped cogwheel, equipped with five teeth ranging from pseudo-1D aryl groups to large planar 2D paddles. A divergent synthetic approach was followed, starting from a pentakis(p-bromophenyl)cyclopentadienyl ruthenium(II) complex as key precursor or from its iodinated counterpart, obtained by copper-catalyzed aromatic Br/I exchange. Subsequent fivefold cross-coupling reactions with various partners allowed high structural diversity to be reached and yielded molecular-gear prototypes with aryl-, carbazole-, BODIPY- and porphyrin-derived teeth of increasing size and length. 相似文献
48.
Dr. Yasunori Minami Prof. Dr. Tamejiro Hiyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(2):391-399
Organo(trialkyl)silanes have several advantages, including high stability, low toxicity, good solubility, easy handling, and ready availability compared with heteroatom-substituted silanes. However, methods for the cross-coupling of organo(trialkyl)silanes are limited, most probably because of their exceeding robustness. Thus, a practical method for the cross-coupling of organo(trialkyl)silanes has been a long-standing challenging research target. This article discusses how aryl(trialkyl)silanes can be used in cross-coupling reactions. A pioneering example is CuII catalytic conditions with the use of electron-accepting aryl- or heteroaryl(triethyl)silanes and aryl iodides. The reaction forms biaryls or teraryls. This design concept can be extended to Pd/CuII-catalyzed cross-coupling polymerization reactions between such silanes and aryl bromides or chlorides and to CuI-catalyzed alkylation using alkyl halides. 相似文献
49.
《Tetrahedron》2019,75(28):3856-3863
Without employing any transition metal, organic solvent and base, a facile, economical and environmentally friendly strategy has been developed for the α-hydroxylation of β-keto esters and β-keto amides with peroxides via radical cross-coupling reaction in water under open-air conditions. This protocol allows a convenient access to various α-hydroxy-β-keto esters and α-hydroxy-β-keto amides with up to 92% yield (34 examples). Moreover, the reaction was successfully scaled up to gram quantity and mechanistic studies showed the radical pathway was involved in this hydroxylation. 相似文献
50.
Jiang Tian Liu Hannes Hase Sarah Taylor Ingo Salzmann Pat Forgione 《Angewandte Chemie (International ed. in English)》2020,59(18):7146-7153
A library of symmetrical linear oligothiophene was prepared employing decarboxylative cross‐coupling reaction as the key transformation. Thiophene potassium carboxylate salts were used as cross‐coupling partners without the need of co‐catalyst, base, or additives. This method demonstrates complete chemoselectivity and is a comprehensive greener approach compared to the existing methods. The modularity of this approach is demonstrated with the preparation of discreet oligothiophenes with up to 10 thiophene repeat units. Symmetrical oligothiophenes are prototypical organic semiconductors where their molecular electrical doping as a function of the chain length can be assessed spectroscopically. An oligothiophene critical length for integer charge transfer was observed to be 10 thiophene units, highlighting the potential use of discrete oligothiophenes as doped conduction or injection layers in organic electronics applications. 相似文献