- Photolysis of 1-alkylcycloalkanols in the presence of (diacetoxyiodo) benzene and I2. Intramolecular selectivity in the β-scission reactions of the intermediate 1-alkylcycloalkoxyl radicals
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The C-C β-scission reactions of 1-alkylcycloalkoxyl radicals, generated photochemically by visible light irradiation of CH2Cl 2 solutions containing the parent 1-alkylcycloalkanols, (diacetoxy)-iodobenzene (DIB), and I2, have been investigated through the analysis of the reaction products. The 1-alkylcycloalkoxyl radicals undergo competition between ring opening and C-alkyl bond cleavage as a function of ring size and of the nature of the alkyl substituent. With the 1-propylcycloheptoxyl, 1-propylcyclooctoxyl, and 1-phenylcyclooctoxyl radicals, formation of products deriving from an intramolecular 1,5-hydrogen atom abstraction reaction from the cycloalkane ring has also been observed. The results are discussed in terms of release of ring strain associated to ring opening, stability of the alkyl radical formed by C-alkyl cleavage, and with cycloheptoxyl and cyclooctoxyl radicals, also in terms of the possibility of achieving a favorable geometry for intramolecular hydrogen atom abstraction.
- Antunes, Carla S. Aureliano,Bietti, Massimo,Lanzalunga, Osvaldo,Salamone, Michela
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p. 5281 - 5289
(2007/10/03)
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- 1,1-DICYCLOPENTADIENYL-3,3-DIMETHYLVANADA(IV)CYCLOBUTANE
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The reaction of 1,3-bis(bromomagnesio)-2,2-dimethylpropane (1b) with dichlorodicyclopentadienylvanadium(IV) (5) gave 1,1-dicyclopentadienyl-3,3-dimethylvanada(IV)cyclobutane (4) in 30percent yield, contaminated with dicyclopentadienylneopentylvanadium(III) (12).Attempts to purify 4 were only partially successful due to its limited stability (t1/2 = 4 h at 25 deg C in cyclopentane).Identification of 4 is therefore based on its having sufficient thermal stability for isolation, on its reaction with bromine to give 1,3-dibromo-2,2-dimethylpropane (2b), and especially on its ESR and 1H NMR spectra.The reaction of 4 with cyclohexanone (15) gave 17 and 18 as the main products; 17 is the aldol dimer of 15, while 18 may be derived from either 4 or 12.Because methylenecyclohexane (16) is not one of the reaction products, it is concluded that 4 does not have a pronounced tendency to fragment to give a metallacarbene (20).
- Seetz, J. W. F. L.,Heisteeg, B. J. J. Van De,Schat, G.,Akkerman, O. S.,Bickelhaupt, F.
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p. 173 - 182
(2007/10/02)
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