- Generation of Aryl Radicals from Aryl Halides: Rongalite-Promoted Transition-Metal-Free Arylation
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A new and practical method for the generation of aryl radicals from aryl halides is reported. Rongalite as a novel precursor of super electron donors was used to initiate a series of electron-catalyzed reactions under mild conditions. These transition-metal-free radical chain reactions enable the efficient formation of C-C, C-S, and C-P bonds through homolytic aromatic substitution or SRN1 reactions. Moreover, the synthesis of antipsychotic drug Quetiapine was performed on gram scale through the described method. This protocol demonstrated its potential as a promising arylation method in organic synthesis.
- Yu, Fazhi,Mao, Runyu,Yu, Mingcheng,Gu, Xianfeng,Wang, Yonghui
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p. 9946 - 9956
(2019/09/04)
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- UVA- and Visible-Light-Mediated Generation of Carbon Radicals from Organochlorides Using Nonmetal Photocatalyst
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Carbon radicals are reactive species useful in various organic transformations. The C-X bond cleavage of organohalides by photoirradiation is a common method to generate carbon radicals in a controlled fashion. The use of organochloride substrates is still a formidable challenge due to the low reduction potential and the high dissociation energy of the C-Cl bond. In this report, we address these issues by using a nonmetal organic molecule with a relatively simple structure as a photocatalyst. In this catalyst (bis(dimethylamino)carbazole), the amino groups increase both the HOMO and LUMO energy levels, especially in the former. As a result, compared to the parent molecule, the new catalyst shows experimentally red-shifted absorption in the visible region and forms an excited state with better reducing capability. This photocatalyst was used in the reduction of unactivated aryl chlorides and alkyl chlorides in the presence of hydrogen atom donor at room temperature. The catalytic system can also be applied to the coupling of aryl chlorides with electron-rich arene and heteroarenes to affect the C-C bond-forming reactions. Our mechanistic study results support the assumption that carbon radicals are formed from the organochlorides via a single-electron-transfer step.
- Matsubara, Ryosuke,Yabuta, Tatsushi,Md Idros, Ubaidah,Hayashi, Masahiko,Ema, Fumitoshi,Kobori, Yasuhiro,Sakata, Ken
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p. 9381 - 9390
(2018/07/25)
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- Palladium-Catalyzed Regioselective Dehydrogenative C–H/C–H Cross-Coupling of Pyrroles and Pyridine N-Oxides
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The palladium-catalyzed cross-dehydrogenative coupling of N-alkylpyrroles and pyridine N-oxides gave the corresponding pyrrolylpyridine N-oxides. Cu(OAc)2·H2O as a co-catalyst with air as the terminal oxidant led to preferential coupling in the β-position, whereas AgOAc as the stoichiometric oxidant resulted in preferential coupling in the α-position. N-(Benzyloxymethyl)pyrrole derivatives were deprotected by hydrogenolysis followed by basic hydrolysis.
- Liu, Shanshan,Tzschucke, C. Christoph
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p. 3509 - 3513
(2016/07/28)
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- Palladium-catalyzed indole, pyrrole, and furan arylation by aryl chlorides
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The palladium-catalyzed direct arylation of indoles, pyrroles, and furans by aryl chlorides has been demonstrated. The method employs a palladium acetate catalyst, 2-(dicyclohexylphosphino)-biphenyl ligand, and an inorganic base. Electron-rich and electron-poor aryl chlorides as well as chloropyridine coupling partners can be used, and arylated heterocycles are obtained in moderate to good yields. Optimization of base, ligand, and solvent is required for achieving best results.
- Nadres, Enrico T.,Lazareva, Anna,Daugulis, Olafs
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experimental part
p. 471 - 483
(2011/04/15)
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- Ring-Centered Heterocyclic Cations and the Direct Heteroarylation of Aromatic and Heterocyclic Compounds
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(matrix presented) The protonation of heterocyclic diazotates (attachment adjacent to a nitrogen atom) yields ring-centered heterocyclic carbocations that are highly reactive. The carbocations were found to alkylate aromatic and heterocyclic compounds, such as benzene, N-methylpyrrole, and 2-aminopyridine, in reactions that are synthetically useful. This carbocation involvement may serve as a paradigm for the cross-linking of DNA by nitrous acid and the anticancer activity of heterocyclic diazotates.
- Song, Fenhong,St. Hilaire, Valentine R.,White, Emil H.
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p. 1957 - 1959
(2008/02/11)
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- PHOTO-ARYLATION III : SYNTHESIS OF 2-HETEROARYLPYRIDINES
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The title compounds were prepared in satisfactory yields by photo-reaction of 2-halopyridine (halogen; I,Br) with five membered heteroaromatics.
- Seki, Koh-ichi,Ohkura, Kazue,Terashima, Masanao,Kanaoka, Yuichi
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p. 2347 - 2350
(2007/10/02)
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- PALLADIUM-PHOSPHINE COMPLEX CATALYZED CROSS-COUPLING REACTION OF 1-METHYL-2-PYRROLYL-MAGNESIUM BROMIDE AND -ZINC CHLORIDE WITH ORGANIC HALIDES
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1-Methyl-2-pyrrolyl-magnesium bromide and -zinc chloride, which were prepared from 1-methyl-2-pyrrolyllithium with MgBr2 and ZnCl2 respectively, reacted with aryl- and heteroaromatic halides to give the corresponding 2-substituted pyrroles in good to excellent yields in the presence of palladium-phosphine complexes as catalysts.
- Minato, Akio,Tamao, Kohei,Hayashi, Tamio,Suzuki, Keizo,Kumuda, Makoto
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p. 5319 - 5322
(2007/10/02)
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