- AN INEXPENSIVE INFLUENCE MODIFICATION OF THE SIMMONS-SMITH REACTION: THE FORMATION OF BROMOMETHYLZINC BROMIDE AS STUDIED BY NMR SPECTROSCOPY
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Bromomethylzinc bromide, prepared from zinc metal and methylene bromide in tetrahydrofuran, gives moderate to good yields of cyclopropanation product when treated with olefins, thus providing an inexpensive alternative to the Simmons-Smith procedure.An NMR study of the reaction between metallic zinc and methylene bromide has been carried out: in addition to bromomethylzinc bromide and dimethylzinc, two further species were observed and tentatively identified as bis(bromomethyl)zinc a di- or tri-zinc compound.
- Fabisch, Bodo,Mitchell, Terence N.
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- The diagnostic substrate bicyclohexane reveals a radical mechanism for bacterial cytochrome P450 in whole cells
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(Figure Presented) On home ground: The reaction mechanisms of bacterial alkane-oxidizing cytochrome P450s were determined in their native environment using a novel diagnostic substrate probe, bicyclohexane, in whole cells and cell-free extracts (see picture). Purified P450cam also oxidizes bicyclohexane. Clear evidence for a substrate-based radical with a lifetime of 75-250 ps was obtained.
- Austin, Rachel N.,Deng, Dayi,Jiang, Yongying,Luddy, Kate,Van Beilen, Jan B.,Ortiz De Montellano, Paul R.,Groves, John T.
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p. 8192 - 8194
(2008/02/08)
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- Carbenes in Constrained Systems, 3. Solid-State Photolysis of Cycloheptane- and Cyclooctanespirodiazirine within Cyclodextrins and Zeolites
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Inclusion complexes of cycloheptanespirodiazirine (1) and cyclooctanespirodiazirine (8) in α-, β-, and γ-cyclodextrin, and faujasite type zeolites (NaX and NaY), have been prepared.The guest-host complexes (1- and 8CD and 1- and 8zeolite) were irradiated with UV light in the solid state and the reaction products were separated from the host and analyzed.Product ratios from photolysis of complexes were compared with those obtained from pure compounds and in solution.Cycloheptanespirodiazirine (1) gives cycloheptene (2), bicycloheptane (3), and methylenecyclohexane (4).Photolysis products from cyclooctanespirodiazirine (8) are cyclooctene (9), bicyclooctane (10), and bicyclooctane (11). 10 results from a 1,5-C-H insertion reaction of the carbene derived from 8.As the cavity size of the cyclodextrins becomes larger, the formation of 10 seems to increase.In β-cyclodextrin and in non-polar solvents substantial amounts of azine were found.In addition to hydrocarbons, photolyses in zeolites afforded alcohols and small amounts of the corresponding ketones. - Keywords: Diazirines / Zeolites / Cyclodextrins / Photochemistry / Carbenes
- Kupfer, Rene,Brinker, Udo H.
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p. 1721 - 1726
(2007/10/03)
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- Use of high pressure in the reduction of organic chlorides with tri-n-butyltin hydride
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The use of the high pressure technique enables reduction of organic halides by tri-n-butyltin hydride to be carried out in the absence of a catalyst or free radical initiator.It leads to a better conservation of the structure of the starting material during the reduction.In the case of some unsaturated halides, a new chemoselectivity has been observed in favour of the addition of the hydride on the carbon-carbon double bond.
- Rahm, A.,Amardeil, R.,Degueil-Castaing, M.
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- Preparation and properties of metallacyclobutanes of nickel and palladium
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Bis(phosphine)-3,3-dimethylnickela- and palladacyclobutanes have been prepared by intramolecular C-H insertion reaction of the corresponding dineopentyl metal complexes.Nickelacyclobutane complexes decompose when heated thereby undergoing competitive carb
- Miyashita, Akira,Ohyoshi, Mayumi,Shitara, Hiroaki,Nohira, Hiroyuki
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p. 103 - 112
(2007/10/02)
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- Platinacyclobutane chemistry: Cis-disubstituted platinacyclobutane complex from bicyclo[4.1.0] heptane
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The methodology for the preparation, isolation, and characterization of platinacyclobutanes from cis-disubstituted cyclopropane derivatives is established. In this case the metallacyclobutane was successfully prepared and characterized from bicyclo[4.1.0]
- Parsons,Jennings
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p. 1435 - 1437
(2008/10/08)
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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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- Hydrogenolysis of Small Cycloalkanes, X. - Catalytic Hydrogenation of Bicycloalkanes
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Dependent on n different products are obtained from bicycloalkanes by hydrogenation on Pt and Pd/C catalysts: from n = 5 onward only methylcycloalkanes of the same ring size; with n = 4 additionally 2-7 percent of cycloheptane is formed; with n = 3 ring enlargement increases to 5-20 percent and with n = 2 cyclopentane is the only product.Mainly butane is formed from bicyclobutane and no intermediate could be detected.Explanations are attempted.The expected products are produced on hydrogenation of methyl-substituted derivatives and spiroalkanes.
- Stahl, Karl-Johannes,Hertzsch, Winfried,Musso, Hans
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p. 1474 - 1484
(2007/10/02)
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- TERMINATION REACTIONS OF C5-C12 CYCLOALKYL RADICALS AND CARBENES
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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.
- Wojnarovits, Laszlo
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p. 1449 - 1452
(2007/10/02)
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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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- Low-temperature Reaction of gem-Dihalocyclopropanes with Activated Magnesium
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The reaction of 7-bromo-7-chlorobicycloheptane and 7-bromo-7-fluorobicycloheptane with activated magnesium in THF at -50 to -40 deg C gave 7-bromobicycloheptane, in addition to 7-chloro- and 7-fluorobicycloheptane, respectively.
- Ando, Teiichi,Muranaka, Takeshi,Ishihara, Takashi
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p. 3227 - 3228
(2007/10/02)
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