- Reductive coupling of aromatic dialkyl acetals using the combination of zinc and chlorotrimethylsilane in the presence of potassium carbonate
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The treatment of aromatic acetals with zinc and chlorosilane in the presence of potassium carbonate in toluene brought about facile and effective reductive coupling to give the corresponding coupling products. Copyright
- Hatano, Bunpei,Nagahashi, Keita,Habaue, Shigeki
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p. 1418 - 1419
(2008/03/14)
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- Substituent Effects on the C-C-Bond Strength, 12. - Thermolysis of Aromatic Pinacol Dimethyl Ethers and Stabilisation Energies of α-Methoxybenzyl Radicals
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The phenyl-substituted pinacol dimethylethers meso- and DL- 5a-d have been prepared by reductive dimerisation of the dimethyl acetals 7a-d of the ketones 8a-d. (1)H NMR spectra and GC-retention times are used to distinguish between the diastereomers, and an X-ray structure analysis of meso-5a confirms these distinctive criteria.The products and the kinetics of the thermolysis reaction of 5a-d have been studied.A linear correlation between ΔG(excit.) (300 deg C) of thermolysis and strain enthalpies HS of 5, or its release DS during the dissoziation into radicals 6, is observed.These correlations do not differ from those of the thermolysis of tetraalkyl-diphenylethanes (1, R = alkyl, S = phenyl).Hence, the methoxy group does not influence the homolysis reaction of the C-C bond in 5 compared to an alkyl group.It is concluded that any stabilisation of the radicals 6 by the alkoxy group is canceled by an extra stabilisation of 5 by the geminal phenyl/methoxy pairs. Key Words: C-C Bond homolysis/ Thermolysis/ Kinetics/ Radical stabilisation
- Birkhofer, Hermann,Beckhaus, Hans-Dieter,Peters, Karl,Schnering, Hans-Georg von,Ruechardt, Christoph
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p. 1693 - 1700
(2007/10/02)
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- The Photochemical Reaction between 1,4-Dicyanonaphthalene and benzyl ethers
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Irradiation of 1,4-dicyanonaphthalene (DCN) and benzyl methyl ether gives the two diastereoisomeric 1-substituted 1,2-dihydronaphthalenes. A stereochemical assignment for these products, and related diastereoisomers pairs is proposed. The reaction occurs via the free radical ions and the low quantum efficiency is due to the slow deprotonation of the radical cation, with only moderate salt effect. In accordance with this scheme, the reaction with benzyl 1-menthyl ether gives a low enantiomeric eccess.
- D'Alessandro, Nicola,Mella, Mariella,Fasani, Elisa,Toma, Lucio,Albini, Angelo
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p. 5043 - 5050
(2007/10/02)
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- Effects of Substituents on the Strength of C-C Bonds, 8. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L-1,2-Dimethyl-1,2-diphenylethylene Glycol Dimethyl Ether
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The heats of combustion of the titel compounds 1 and 2 were measured calorimetrically with the result (kcal mol-1, s.d. in parentheses)ΔHc0 = -1880.1 (+/-0.6) and -2373.3 (+/-1.4).The heat of vaporisation of 1 ΔHv/su
- Dogan, Barbara,Beckhaus, Hans-Dieter,Birkhofer, Hermann,Ruechardt, Christoph
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p. 1365 - 1368
(2007/10/02)
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- Surface photochemistry: the photolysis of α-methoxy acetophenones on silica gel
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The photolysis of α-methoxy acetophenones 1a-1e adsorbed on silica gel show a significant deviation from the course of reaction in methanol.The results are discussed in terms of conformational control and restricted movement of the radical through adsorption on silica gel.Factors affecting the efficiency of modification of photochemical reactivity on silica gel surface have been examined.
- Mayo, Paul de,Ramnath, N.
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p. 1293 - 1296
(2007/10/02)
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- Photoinduced electron transfer C-C bond cleavage reactions; oxidations and isomerizations
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We have shown that radical cations generated by photoinduced electron transfer (ET) in 1,2-diarylethanes, aryl pinacols, and their derivatives undergo fragmentation reactions.In the presence of oxygen oxidative products are obtained.Timerresolved laser flash photolysis and other ancillary techniques have permitted us to define the mechanisms of certian oxidative processes observed.
- Reichel, L. W.,Griffin, G. W.,Muller, A. J.,Das, P. K.,Ege, Seyhan N.
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p. 424 - 436
(2007/10/02)
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