- Cross cage interactions in substituted bicyclo[1.1.]pent-1-yl radicals. Dissociation to [1.1.1]propellane
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A series of 3-substituted bicyclo[1.1.1]pent-1-yl radicals, including the 3-fluoro derivative, was generated by bromine atom abstraction from 1-bromo-3-substituted-bicyclo[1.1.1]pentanes and examined by EPR spectroscopy. The exceptionally large hyperfine splittings obtained from magnetic nuclei of the 3-substituents indicated that cross cage electronic interactions were substantial in these species. Bromine atom abstraction by triethylsilyl radicals from 1-bromo-3-fluorobicyclo[1.1.1]pentane was found to take place more rapidly than bromine abstraction from the unsubstituted parent, i. e., the fluorine substituent mediated a significant polar effect. Evidence was found of a novel disproportionation process in which the γ-fluorine atom was transferred from the 3-fluoro radical to a triethylsilyl or to a second bicyclo[1.1.1]pent-1-yl radical; an analogous chlorine atom transfer process was found for the 3-chloro radical. Ab initio MO calculations (6-31G* basis with electron correlation up to MP4) on the 3-fluoro- and 3-methyl-substituted radicals indicated that loss of the substituent to give [1.1.1]propellane would be comparatively easy for both species.
- Adcock, William,Binmore, Gavin T.,Krstic, Alexander R.,Walton, John C.,Wilkie, John
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p. 2758 - 2766
(2007/10/02)
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- Toward a molecular-size "Tinkertoy" construction set. Preparation of terminally functionalized [n]staffanes from [1.1.1]propellane
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A facile but low-yield synthesis of [n]staffanes (the oligomers of [1.1.1.]propellane 1, n =1-5) functionalized on one or both ends is described, and their properties are summarized. The substituents are -COOCH3, -n-C4H9, -C6H5, -Br, -I, and -SCOCH3, and their conversion to others, such as -COOH, -COCH3 and -SH, is demonstrated. It is proposed that these rod-shaped molecules will be useful in the development of a molecular-size civil engineering construction set analogous to children's toy construction sets.
- Kaszynski, Piotr,Friedli, Andrienne C.,Michl, Josef
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p. 601 - 620
(2007/10/02)
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- Reactions of [1.1.1]propellane
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The free radical addition reactions of [1.1.1]propellane (1) are described in some detail and allowed the preparation of a wide variety of 1,3-disubstituted bicyclo[1.1.1]pentanes. The reaction of 1 with free radicals was more rapid than that of bicyclo[1.1.0]butane (2), whereas bicyclo[2.1.0]pentane (3) was relatively inert. In some cases the free-radical additions led to oligomers, and in the case of tetrahydrofuran addition the chain-transfer constant was measured. The addition of thiophenol to 1 followed by reduction with the lithium radical anion from 4,4′-di-tert-butylbiphenyl gave 1-lithiobicyclo[1.1.1]petane, from which a variety of 1-substituted bicyclo[1.1.1]pentanes may be prepared. In the Baeyer-Villiger oxidation of 1-benzoylbicyclo[1.1.1]pentane, the terf-butyl group migrated in preference to the bicyclopentyl group. Conversion of the ketone to the tosylhydrazone followed by base treatment gave products of the type expected from the corresponding carbene. The reaction of 1 with NO in carbon disulfide gave a unique reaction in which nitro and thiocyano groups were introduced. The reactions of 1, 2, and 3 with NO2 also were examined. Whereas 1 gave 1,3-dinitrobicyclo[1.1.1]pentane, the other hydrocarbons followed different reaction paths. The reaction of 1 with electron-deficient alkenes and alkynes are described in some detail and are compared with the corresponding reactions of 2 and 3. Here, the relative reactivities of 1 and 2 were often comparable but varied considerably with the reagent used. Again, 3 was relatively unreactive. The reaction of 1 with Rh(I) gave a dimer, and evidence is presented for a metallocarbene intermediate.
- Wiberg, Kenneth B.,Waddell, Sherman T.
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p. 2194 - 2216
(2007/10/02)
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