1755-05-1Relevant articles and documents
Functionalization of saturated hydrocarbons. High temperature bromination of octahydropentalene. Part 19
Günba?, Duygu D.,Algi, Fatih,H?kelek, Tuncer,Watson, William H.,Balci, Metin
, p. 11177 - 11183 (2005)
The synthesis and thermal bromination of octahydropentalene was studied. The reaction afforded 1a,3a,4b,6b-tetrabromo-1,2,3,4,5,6-hexahydropentalene (14) with remarkable regio- and stereospecificity. The structure of the product was determined by 1H and 13C NMR data and single X-ray structural analysis. The treatment of octahydropentalene with tenfold bromine gave the octabromopentalene derivative. The formation mechanism of the products is discussed.
Hydrogenation of Ru(1,5-cyclooctadiene)(η3-C3H5)2 over black platinum. A low-temperature reactive deposition of submonolayer quantities of ruthenium atoms on platinum with real time control over surface stoichiometry
Lee, Christopher E.,Tiege, Paul B.,Xing, Yue,Nagendran, Jayan,Bergens, Steven H.
, p. 3543 - 3549 (2007/10/03)
Black Pt effected the hydrogenation of Ru(COD)(η3-C3H5)2 (1; COD is 1,5-cyclooctadiene) by dihydrogen gas (pressure ~ 1 atm) at -10 °C in hexanes. The hydrogenation resulted in adsorption of Ru adatoms by the surface of Pt with concomitant formation of propane, cyclooctane, and small amounts of cis-bicyclo[3.3.0]octane and n-octane. Compound 1 did not react with dihydrogen gas under these conditions in the absence of Pt. The total amount of cyclooctane, bicyclo[3.3.0]octane, and n-octane in solution was equal to the amount of 1 consumed at all stages of the hydrogenation. The lifetimes of the organic fragments on the surface were short on the time scale of the hydrogenation. It was therefore possible to observe in real time both the stoichiometry and the activity of the evolving Ru-Pt surface by monitoring the concentrations of either 1 or the C8 product hydrocarbons in solution. There was a kinetic burst during the initial stages of the hydrogenation that ended after deposition of 0.2-0.5 equiv of Ru versus Pt(surface) (Pt(surface) is an active site on black Pt). The rate decreased after the burst and then increased as more Ru was deposited on Pt to reach a maximum, constant rate after deposition of 1.5-1.8 equiv of Ru. Cyclic voltammograms recorded in 1.0 M H2SO4 of the bare surface, of the surface after adsorption of a monolayer of carbon monoxide, and of the surface in the presence of methanol showed that coverage of Pt by Ru was essentially complete after the maximum, constant rate was achieved during hydrogenation of 1. The surface area of a Ru surface resulting from hydrogenation of 2.7 equiv of 1 was 67% that of the original Pt surface according to the charge associated with oxidation of an adsorbed monolayer of carbon monoxide. Anodic stripping of Ru showed that the total of C8 hydrocarbon products in solution after hydrogenation of 1 equaled the amount of Ru deposited on Pt. A catalyst surface resulting from hydrogenation of 0.11 equiv of 1 was up to ~ 14 times more active than bare Pt for the potentiodynamic oxidation of methanol ([MeOH] = 1.0 M, [H2SO4] = 0.5 M, 40 °C, sweep rate 5 mV/s). A catalyst surface resulting from hydrogenation of 0.33 equiv of 1 oxidized methanol potentiostatically at 0.158 V (vs SCE, [MeOH] = 0.5 M, [H2SO4] = 0.5 M, 25 °C) for 45 min with ~ 13 times the activity of Pt under the same conditions. A catalyst surface resulting from deposition of 0.8 equiv of Ru oxidized methanol potentiostatically at 0.256 V (vs SCE) under the above conditions for a total of 1.5 h with negligible dissolution of Ru into the electrolyte.
Evidence for Single Electron Transfer in the Reactions of Lithium Dimethylcuprate with Alkyl Halides
Ashby, E. C.,Coleman, David
, p. 4554 - 4565 (2007/10/02)
A variety of methods have been utilized to explore the occurence of radical intermediates and free-radical chain processes initiated by electron transfer in the reactions of lithium dimethylcuprate with alkyl halides.The effect of leaving group, nature of the cuprate species, and ratio of cuprate to substrate, solvent, hydrogen atom donor, and other additives on the rate of and product distribution were investigated by using a cyclooctenyl radical probe.The presence of significant amounts of radicals strongly supports single electron transfer (SET) as a major pathway for the reaction of secondary iodides with LiCuMe2.There is some evidence of single electron transfer also accurring with secondary bromides, but tosylates appear to be reacting entirely by a SN2-like pathway.The role of dicyclohexylphosphine (DCPH) as an additive in the reaction was investigated with the result that it was shown to be capable of behaving in a unique manner depending on wheter the substrate is an alkyl iodide or bromide.The product distribution, rate, and effect of p-dinitrobenzene on the reaction of 5-iodo-1-cyclooctene were compared with three other probes and the results demonstrate that at least three reaction pathways are involved to varying degrees.These pathways could involve the initiation of free radicals or radical anion (SRN1) chain processes. these studies also demonstrate how changes in the substrate can alter the predominant reaction pathways that are followed.
The Use of 5-Halocyclooctenes as a Radical Probe. Reactions with Lithium Aluminum Hydride
Ashby, E.C.,Pham, Tung N.
, p. 3598 - 3602 (2007/10/02)
The 5-halocyclooctenes have been studied as a radical probe in their reactions with lithium aluminum hydride (LiAlH4) in order to detect the occurrence of radical intermediates and also to evaluate the effectiveness of these compounds as radical probes.Also the 4-cyclooctenyl radical was trapped by dicyclohexylphosphine (DCPH), dicyclohexylphosphine deuteride (DCPD), and cyclohexadiene.For the iodide, and to a lesser extent the bromide, radical intermediates were found to be a major component in the reaction since the bicyclo hydrocarbon was the major product.No evidence for radical intermediates was found for reactions of the correspon ding chloride or tosylate with LiAlH4.It is concluded that 5-iodocyclooctene is an effective radical probe for those reactions where radical intermediates are involved
Photochemistry of Alkenes. 9. Medium-sized cycloalkenes
Kropp, Paul J.,Mason, J. Derek,Smith, Gardiner F. H.
, p. 1845 - 1849 (2007/10/02)
The behavior of three medium-sized cycloalkenes cyclooctene (10), cyclodecene (17) and cyclododecene (21) on direct irradiation in pentane and methanol solution has been studied.The results are summarized in Tables 1-3.Irradiation of medium-sized cycloalkenes is a convenient procedure for the preparation of bicyclic products (cf. 13, 14, 19, 20 and 23) through transannular insertion reactions of carbene intermediates (cf. 11, 18, and 22) thought to arise from rearrangement of the 1 state via a 1,2-hydrogen shift.The formation of trans-decalin (20) is in contrast to the reported formation of the cis isomer on base-initiated decomposition of the corresponding tosylhydrazone.None of the three cycloalkenes 10, 17, or 21 underwent competing nucleophilic trapping of the 1 state in methanol, in contrast with other alkenes previously studied.However, cyclododecene (21) afforded the methyl ether 25, which apparently resulted from protonation of the 1(?,?*) state, and the epoxide 26, which is thought to arise from electron transfer to oxygen by the 1 state followed by protonation of the resulting superoxide ion and oxidation of unreacted cyclododecene (21).
TERMINATION REACTIONS OF C5-C12 CYCLOALKYL RADICALS AND CARBENES
Wojnarovits, Laszlo
, p. 1449 - 1452 (2007/10/02)
Reactions of C5-C12 cycloalkyl radicals and carbenes produced during radiolysis, vacuum-u.v. photolysis, and decomposition of cycloalkanone p-tosylhydrazones were investigated.The disproportionation to combination ratios of radicals are ca. 1 and agree with the ratios of linear secondary radicals.The disproportionation smaller cycloalkyl radicals yields cis-cycloalkenes and cycloalkanes; from C9 and C10 cis- and trans-cycloalkenes and cycloalkanes and from C11 and C12 trans-cycloalkenes and cycloalkanes are produced.Both atoms of H2 given off in the elimination reaction from excited cycloalkane molecules orginate from the same carbon atom and in this process carbenes are formed.Rearrangement of small (C5, C6) and large (C11, C12) cycloalkylcarbenes in the solvent of the given cycloalkane occurs by 1,2-hydrogen migration.C7-C10 carbenes rearrange both by hydrogen atom migration and transannular insertion.
CARBENE-CARBENE REARRANGEMENTS AS A ROUTE TO 1,5-DIHYDROPENTALENE
Brinker, Udo H.,Fleischhauer, Ilona
, p. 4495 - 4502 (2007/10/02)
1,5-Dihydropentalene (4) is formed as the main product on treatment of trans-1,2-bis(2,2-dibromocyclopropyl)ethene 3 with methyllithium at -40 deg C.In addition the reaction affords 1- and 2-propadienylcyclopentadienes (5a) and (5b), and trans-1,2,4,6,7-octapentaene (6), new C8H8 isomers.Diels-Alder adducts of 4, 5a and 5b were obtained in the reaction with perfluorobut-2-yne.The formation of 1,5-dihydropentalene 4 is explained by a double ring expansion sequence involving consecutive carbene-carbene rearrangements with 1,3-carbon and subsequent 1,2-hydrogen shifts, supported by the reaction of double labelled ((13)C-depleted) 3.From readily available 3 at low temperatures formation and fusion of two 5-membered rings are achieved in one step.
