- Radiolytic Generation of Radical Cations in Xenon Matrices. Tetramethylcyclopropane Radical Cation and Its Transformations
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Radiolytic generation of radical cations in xenon matrices containing electron scavengers is illustrated by studying the 1,1,2,2-tetramethylcyclopropane radical cation.Dilute and concentrated solutions of tetramethylcyclopropane in xenon without electron scavengers and neat tetramethylcyclopropane yielded neutral radicals upon γ-irridation.Speculation on the mechanisms of radical formation is presented.The radical species observed in the γ-irridation of neat tetramethylcyclopropane appears to be identical with the paramagnetic species observed in CF2ClCFCl2 above 120 K, suggesting that a neutral radical rather than the ring-opened distonic radical cation is observed in the CF2ClCFCl2 matrix.
- Qin, X.-Z.,Trifunac, A. D.
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- Bimolecular chemistry of dimethylcarbene
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A new non-nitrogenous precursor of dimethylcarbene has been synthesized. Photolysis of 10,10′-dimethyltricyclo[4.3.1.01,6]deca-2,4-diene in solution with 254 nm light produces dimethylcarbene. Previously unknown intermolecular reactions of dimethylcarbene have been observed.
- Likhotvorik, Igor R.,Tippmann, Eric,Platz, Matthew S.
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p. 3049 - 3051
(2007/10/03)
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- Photochemical ring expansion of tetramethylcyclobutanone revisited: Angular dependence of electronic absorption of singlet carbenes
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Tetramethyltetrahydrofuranylidine, produced by the photochemical ring expansion of the corresponding cyclobutanone, has been characterized by IR and UV/Vis spectroscopy in a low-temperature N2 matrix. The angular dependence of the UV/Vis spectra of this and related carbenes is explored by ab initio calculations.
- Matsumura,Ammann,Sheridan
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p. 1843 - 1846
(2007/10/02)
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- Dehalogenation of Geminal Dihalocyclopropanes, α,α-Dichlorocyclobutanones, and Haloketones by Means of Magnesium Anthracene*3THF
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1,1-Dichloro-2,2,3,3-tetramethylcyclopropane (1a), 7,7-dichloro- and 7,7-dibromonorcarane (1b) react with magnesium anthracene*3THF (2) under stepwise radical reduction to give 9a,b, 11a,b and 10, carbene products 6a,a',b and 7a,b, and the alkylation products 4a,b and 5a,b, respectively.The distribution of the reaction products is strongly dependent upon the substrate and upon the reaction conditions: for instance, 1a in toluene undergoes a highly selective reduction to yield 9a, whereas in THF at low temperature 4a and 5a predominate.The reaction course proposed for the reaction of 1a with 2 is supported by deuteration experiments. α,α-Dichlorocyclobutanones 12a-e can be reduced with 2 to give α-chlorocyclobutanones 13a-e in moderate to good yields; 12d is thereby converted in high purity into endo-13d.The reduction of 2-haloketones 15a-f with 2 in THF to the ketones 16a-f is possible only in low or moderate yields.
- Bogdanovic, Borislav,Schlichte, Klaus,Westeppe, Uwe
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- ESR STUDIES OF THE RING OPENING OF CYCLOPROPANE RADICAL CATIONS IN FREON MATRICES
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The radical cations of cyclopropane and several of its methyl derivatives have been characterized by ESR spectroscopy following their generation by γ irradiation of dilute solutions of the parent compounds in Freon matrices at 77 K.In the CFCl3, CF3CCl3, and CF2ClCCl3 matrices, only the ring-closed species is usually observed in the accessible temperature range up to ca 160 K.In the CFCl2CF2Cl matrix, however, the ring-closed radical cations initially formed at 77 K undergo ring opening between 83 and 110 K, the more highly substituted radical cations requiring a higher temperature for this transformation.The ring-closed radical cations are 2A1 species for C2V symmetry, the most substituted cyclopropane C-C bond being elongated with the spin density largely confined to the basal carbons in a face-to-face (90o, 90o) structure.In the ring-opened radical cations, the radical center is localized on the most substituted carbon atom following the breaking of the weakened C-C bond of the ring-closed species.The radical conformations of the ring-opened species have been determined, the RCH2CH2. center produced from cyclopropane having a bisected conformation while the RCH2CMe2. center obtained from 1,1,2,2-tetramethylcyclopropane is eclipsed, as expected for the presence of α-methyl substituents at the radical site.The nature of the putative carbocation center in the ring-opened radical cations is discussed with reference to recent proposals that this center is strongly coordinated to an electrophile (Cl- or RCl) thereby negating the requirement for an orthogonal structure.Consideration of the strong matrix dependence of the ring-opening reaction suggests a possible solvation effect, however, in which the CFCl2CF2Cl matrix assists the twisting of one of the CR1R2 groups at the most substituted bond, leading to the rupture of this one-electron ? bond.A strong solvation effect also explains why ring-opening can occur in a suitable polar solvent despite theoretical calculations of unfavorable energetics for a similar gas-phase reaction.Experiments are also described on spirooctane, the cyclopropane ring undergoing scission at the CH2-CH2 bond of this radical cation to give an RCH2. radical center.This radical then undergoes a H-atom abstraction with a neutral spirooctane molecule in the CFCl2CF2Cl matrix at higher temperature to give the spirooct-6-yl radical.
- Qin, Xue-Zhi,Williams, Francon
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p. 6301 - 6314
(2007/10/02)
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- STREREOSPECIFIC CYCLOPROPANE SYNTHESIS FROM γ-STANNYL ALCOHOLS
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γ-Stannyl tertiary alcohols and γ-stannyl benzyl alcohols form cyclopropanes strereospecifically on treatment with acid, with inversion of configugation at both carbon atoms.
- Fleming, Ian,Urch, Christopher J.
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p. 173 - 192
(2007/10/02)
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- STEREOSPECIFIC CYCLOPROPANE SYNTHESIS FROM Γ-STANNYL ALCOHOLS
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Tertiary and benzyl alcohols with a γ-trialkyltin group from cyclopropanes stereospecifically on treatment with acid, with inversion of configuration at both carbon atoms.
- Fleming, Ian,Urch, Christopher J.
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p. 4591 - 4594
(2007/10/02)
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- Bis(Iodomethyl) Mercury as a CH2 Transfer Reagent
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Bis(iodomethyl) mercury, Hg(CH2I)2, is an effective transfer agent of one CH2 group to olefins to form cyclopropanes.Transfer of the second group (i.e., from ICH2HgI) is not a favourable process.However, the ICH2HgI/Ph2Hg or the ICH2HgI/(PhCH2)2Hg couples serve to transfer the second CH2 group to olefins.
- Seyferth, Dietmar,Haas, Carol K.,Dagani, Doron
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p. 111 - 118
(2007/10/02)
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- REARRANGEMENT OF CYCLOPROPYL, SUBSTITUTED VINYL AND ALKYL GROUPS TO DIVALENT CARBON.
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The relative carbenic migratory abilities of cyclopropyl, β,β-dimethylvinyl, methyl,ethyl and isopropyl groups have been determined.
- Kraska, A. R.,Cherney, L. I.,Shechter, H.
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p. 2163 - 2166
(2007/10/02)
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- Configuration and 13C NMR Spectra of Alkylcyclopropane Derivatives
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Eight alkylcyclopropane derivatives were prepared in a conventional manner and analysed by 13C NMR spectroscopy.Additivity parameters were calculated from the chemical shifts of the endocyclic carbons, and the configurational structures derived for these compounds are confirmed by the internal coherence found for this set of parameters.
- Touillaux, R.,Meerssche, M. Van,Dereppe, J. M.,Leroy, G.,Weiler, J.,Wilante, C.
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- PHOTOCHEMISTRY OF ALKYL HALIDES - VII. CYCLOPROPANATION OF ALKENES
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The previously observed cyclopropanation of alkenes by irradiation of diiodomethane (1) in their presence has been studied in more detail and found to be a synthetically useful procedure which is significantly less subject to steric effects than the traditional Simmons-Smith method.The results from photocyclopropanation of a variety of alkenes are summarized in Tables 1 and 3-4.In a number of cases the photochemical procedure afforded improved results over the Simmons-Smith method, particularly with sterically congested alkenes.Cycloalkenes showed relative rates of photocyclopropanation as a function of ring size similar to those of the Simmons-Smith method (Table 5).However, the photocyclopropanation reaction exhibited steadily increasing relative rates with increasing substitution about the double bond-in contrast with the Simmons-Smith method (Table 6), in which steric effects offset increasing nucleophilicity of the alkene with increasing substitution.The α-iodocation 2 is suggested as the methylene transfer species.In the presence of lithium bromide cation 2 was trapped to afford bromoiodomethane.
- Kropp, Paul J.,Pienta, Norbert J.,Sawyer, Joy A.,Polniaszek, Richard P.
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p. 3229 - 3236
(2007/10/02)
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