- Cobalamin-Catalysed Chemical Reactions: Probing the Role of the Nucleotide Loop
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The nucleotide loop in the vitamin B12 structure affects its biological and physicochemical properties, but its role in cobalamin-catalysed reactions still remains disputable. Herein, we show the synthesis of a series of model compounds includi
- Karczewski, Maksymilian,Ociepa, Micha?,Gryko, Dorota
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- Photodriven Dehydrogenative Homocoupling of Benzylic C-H Bonds Forming Strained C-C Bonds
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A photoinduced dehydrogenative homocoupling reaction of alkylarenes is reported. Gaseous hydrogen is evolved as the sole byproduct and neither oxidants nor hydrogen acceptors are required. The present reaction offers an environmentally benign and atom-economical means for forming sterically strained C-C single bonds. It also gives a remarkable example of photodriven reactions overcoming a considerable rise in energy.
- Ishida, Naoki,Son, Mingon,Kawasaki, Tairin,Ito, Misato,Murakami, Masahiro
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p. 2067 - 2070
(2021/10/14)
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- Controlling the photochemical reactions of alkenes by light-path length effects of a microchannel reactor
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Photoirradiation of Me2CO-H2O solution of pent-4-en-1-ol (1a) with a high-pressure mercury lamp in a test tube gave 8-hydroxyoctan-2-one (3a) in 66 % yield along with oxetane (4a) and the isomer (4a') in 10 % yield. Irradiation of the running Me2CO-H2O solution of 1a in the flow system of a microchannel reactor (MCR) gave mainly 4a. The photoreaction of 1,1-diphenylethene (2a) with triethylamine gave a Markovnikov-type adduct (5a) and an anti-Markovnikov-type adduct (6a). The use of the MCR enhanced the production of 5a. These phenomena were explained by the light-path length effects of the MCR.
- Yamashita, Toshiaki,Matsushita, Shuhei,Nagatomo, Takuya,Yamauchi, Ryosuke,Yasuda, Masahide
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p. 111 - 126
(2013/02/25)
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- Nitrous oxide reduction-coupled alkene-alkene coupling catalysed by metalloporphyrins
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Porphyrin complexes of iron, manganese and cobalt catalysed reductive dimerization of alkenes with NaBH4 under N2O. The reaction system using FeIII porphyrin generated an FeI porphyrin intermediate that reduced N2O to regenerate FeIII porphyrin.
- Saito, Shunsuke,Ohtake, Hiro,Umezawa, Naoki,Kobayashi, Yuko,Kato, Nobuki,Hirobe, Masaaki,Higuchi, Tsunehiko
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supporting information
p. 8979 - 8981
(2013/09/24)
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- Controlling parameters for radical cation fragmentation reactions: Origin of the intrinsic barrier
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C - C bond cleavages of radical cations of 2-substituted benzothiazoline derivatives were investigated to determine the parameters controlling the fragmentation rate constants. In spite of the low oxidation potentials of the compounds, fragmentation rate constants greater than 1 x 106 s -1 could be achieved through weakening of the fragmenting bond by substituents that stabilize the radical fragment and exert steric crowding. A quantitative assessment of the relative roles of radical stabilization vs. steric effects to weaken the fragmenting C - C bond was achieved through DFT calculations. The calculated activation enthalpies matched reasonably well with the experimentally determined values. A thermokinetic analysis revealed that the fragmentations of benzothiazoline radical cations have relatively large intrinsic kinetic barriers, ascribed to the delocalized nature of the product radical and cation fragments. Interestingly, the same factors that lead to the large intrinsic barriers led, simultaneously, to large thermodynamic driving forces for the fragmentations, which should lead to lower activation barriers. These effects oppose each other kinetically and provide important insight into the design of fast radical ion fragmentation reactions.
- Shukla, Deepak,Liu, Guanghua,Dinnocenzo, Joseph P.,Farid, Samir
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p. 744 - 757
(2007/10/03)
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- Mechanistic investigation of a novel vitamin B12-catalyzed carbon-carbon bond forming reaction, the reductive dimerization of arylalkenes
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In the presence of catalytic vitamin B12 and a reducing agent such as Ti(III)citrate or Zn, arylalkenes are dimerized with unusual regioselectivity forming a carbon-carbon bond between the benzylic carbons of each coupling partner. Dimerization products were obtained in good to excellent yields for mono- and 1,1-disubstituted alkenes. Dienes containing one aryl alkene underwent intramolecular cyclization in good yields. However, 1,2-disubstituted and trisubstituted alkenes were unreactive. Mechanistic investigations using radical traps suggest the involvement of benzylic radicals, and the lack of diastereoselectivity in the product distribution is consistent with dimerization of two such reactive intermediates. A strong reducing agent is required for the reaction and fulfills two roles. It returns the Co(II) form of the catalyst generated after the reaction to the active Co(I) state, and by removing Co(II) it also prevents the nonproductive recombination of alkyl radicals with cob(II)alamin. The mechanism of the formation of benzylic radicals from arylalkenes and cob(I)alamin poses an interesting problem. The results with a one-electron transfer probe indicate that radical generation is not likely to involve an electron transfer. Several alternative mechanisms are discussed.
- Shey, Justin,McGinley, Chris M.,McCauley, Kevin M.,Dearth, Anthony S.,Young, Brian T.,Van der Donk, Wilfred A.
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p. 837 - 846
(2007/10/03)
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- Photodecarboxylation of arylacetic acids induced by light-sensitive Hg2F2
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Photolysis of arylacetic acids in argon-saturated acetonitrile in the presence of Hg2F2 gives the corresponding 1,2-diarylethanes as the major product via a radical pathway. This reaction offers an interesting procedure for selective decarboxylation of arylacetic acids with the assistance of a light-sensitive compound.
- Habibi, Mohammad H.,Farhadi, Saeid
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p. 2821 - 2824
(2007/10/03)
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- Photoinduced Decarboxylation of Aryl-substituted Carboxylic Acids Using HgO. A New Photo-Kolbe Reaction Pathway
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Photoassisted decarboxylation of several arylcarboxylic acids using HgO in argon-saturated organic solvents at 25 °C gives dimeric products in good yield via homocoupling of arylalkyl intermediates.
- Habibi, Mohammad H.,Farhadi, Saeid
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p. 776 - 777
(2007/10/03)
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- Photochemistry of two diphenyl β,γ-enones and a series of methyl- and phenyl-substituted α-phenyl ketones
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The photochemistry of the diphenyl β,γ-enones 2 and 3 and the methyl- and phenyl-substituted α-phenyl ketones 4-9 has been studied, using mainly benzene as solvent.Irradation of 2 with λ 300 nm leads to the 1,3-acyl shift (1,3-AS) product 17, relatively small amounts of the decarbonylation products 15 and 16, and the photo-oxidation products benzophenone (18) and the α,β-unsaturated aldehyde 19.Direct irradation of the 1,3-AS product 17 yields 15, 16, 18 and 19, but no 2.Direct irradation of 3 with λ 350 nm leads mainly to the formation of 1,3-AS products (E)- and (Z)-22, the decarbonylation products (E)- and (Z)-20 and 21 and, in addition, a small amount of the cis-di-?-methane isomer 23.Direct irradation of the substituted α-phenyl ketones 4, 5, 8 and 9 with λ 300 nm leads predominantly to the formation of the radical coupling products 2,3-butanedione and 24-27, respectively, whereas 6 and 7 yield 1,2-diphenyl-1,2-ethanedione and the respective 24 and 25.The acetone-sensitized irradation of 4 leads to 4-phenyl-2-butanone (33) in addition to 2,3-butanedione and 1,2-diphenylethane (24).
- Koppes, Margareth J. C. M.,Crabbendam, Astrid M.,Cerfontain, Hans
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p. 676 - 683
(2007/10/02)
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- SYNTHESIS AND CYTOCHROME P-450-LIKE REACTIVITY OF POLYPEPTIDE-BOUND PORPHINATOIRON(III)
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Polypeptide-bound porphinatoiron(III) was synthesized.This polymer could catalyze the hydroxylation of aniline with H2O2 more effectively, and catalyze the monooxygenase-type oxidation of olefins more selectively in the porphinatoiron (III)-O2-NaBH4-Me4NOH system than non-bound porphinatoiron.
- Mori, Takashi,Santa, Tomofumi,Hirobe, Masaaki
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p. 5555 - 5558
(2007/10/02)
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