- Selective enzymatic epoxidation of dienes: Generation of functional enantiomerically enriched diene monoepoxy monomers
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Enantiomerically enriched diene monoepoxides were selectively synthesized using oxidases from Pseudomonas sp. and chloroperoxidase from Caldariomyces fumago. These monoepoxides are useful monomers for generating functional chiral polymeric materials.
- Hu, Shanghui,Gupta, Pankaj,Prasad, Ashok K,Gross, Richard A,Parmar, Virinder S
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- Total Syntheses of (±)-Isosteviol and (±)-Beyer-15-ene-3β,19-diol by Manganese(III)-Based Oxidative Quadruple Free-Radical Cyclization
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Tetraene 1 was prepared in nine steps from the known propargylic alcohol 7 in 17% overall yield or as a 2:1 E/Z mixture in only five steps in 7% overall yield. Oxidative cyclization of 1 with 2 equiv of Mn(OAc)3·2H2O and 1 equiv of Cu(OAc)2 in MeOH at 25 °C provided 35% of tetracycle 2. Further elaboration provided (±)-isosteviol (3) in six steps in 51% yield and (±)-beyer-15-ene-3β,19-diol in four steps in 17% yield.
- Snider, Barry B.,Kiselgof, Jane Y.,Foxman, Bruce M.
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- Kinetics and Mechanism of Thermal Decomposition of Bis(Η3-Allyl)Nickel Complexes
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Abstract: The kinetics of thermal decomposition of bis(η3-allyl) nickel complexes in various media is studied. The specific features of the mechanism are determined, including the combination of the stages of trans-cis isomerization of Niall2 and the bimolecular decomposition of the cis-isomer with diallyl formation. The effect of autocatalytic decomposition of complexes with metallic nickel is been detected. The qualitative dependences of the process rate on the nature of the solvent and the structure of the allyl ligand are determined. The activation parameters of individual steps, consistent with quantum chemical calculations, are found.
- Flid,Zamalyutin,Shamsiev,Katsman
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p. 113 - 117
(2019/05/27)
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- 2,2,5,5-Tetramethyltetrahydrofuran (TMTHF): A non-polar, non-peroxide forming ether replacement for hazardous hydrocarbon solvents
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An inherently non-peroxide forming ether solvent, 2,2,5,5-tetramethyltetrahydrofuran (2,2,5,5-tetramethyloxolane), has been synthesized from readily available and potentially renewable feedstocks, and its solvation properties have been tested. Unlike traditional ethers, its absence of a proton at the alpha-position to the oxygen of the ether eliminates the potential to form hazardous peroxides. Additionally, this unusual structure leads to lower basicity compared with many traditional ethers, due to the concealment of the ethereal oxygen by four bulky methyl groups at the alpha-position. As such, this molecule exhibits similar solvent properties to common hydrocarbon solvents, particularly toluene. Its solvent properties have been proved by testing its performance in Fischer esterification, amidation and Grignard reactions. TMTHF's differences from traditional ethers is further demonstrated by its ability to produce high molecular weight radical-initiated polymers for use as pressure-sensitive adhesives.
- Byrne, Fergal,Forier, Bart,Bossaert, Greet,Hoebers, Charly,Farmer, Thomas J.,Clark, James H.,Hunt, Andrew J.
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supporting information
p. 3671 - 3678
(2017/08/15)
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- Gold(I)-catalyzed intermolecular [2+2] cycloaddition of alkynes with alkenes
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The gold(I)-catalyzed intermolecular reaction of terminal alkynes with alkenes leads to cyclobutenes. The use of sterically hindered cationic Au(I) complexes as catalysts is key for the success of this reaction.
- Lopez-Carrillo, Veronica,Echavarren, Antonio M.
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supporting information; experimental part
p. 9292 - 9294
(2010/11/03)
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- Factors controlling photochemical cleavage of the energetically unfavorable Ph-Se bond of alkyl phenyl selenides
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(Chemical Equation Presented) Primary photochemical paths of alkyl phenyl selenides (1) were investigated, and an origin of large deviations in the chemical yields of products obtained by carbon radical reactions induced by photolysis of phenyl selenides was clarified. KrF excimer laser photolyses of n-pentyl phenyl selenide (1a) yielded 1-pentene (2a), n-pentane (3a), n-decane (4a), dipentyl selenide (5a), benzene (6), dipentyl diselenide (7a), and diphenyl diselenide (7) as major photoproducts, with compounds 2a, 3a, 4a, 5a, and 7 formed by pentyl-Se bond cleavage, and 5a, 6, and 7a by Ph-Se bond cleavage. The selectivity of the photoproducts revealed the occurrence of an unexpected amount of Ph-Se bond cleavage (35% in n-hexane at 248 nm) during photolysis. Solvent viscosity, wavelength of light, and the structure of alkyl substituents were the major factors that controlled Ph-Se bond cleavage. The ratio of Ph-Se bond cleavage decreased with increasing solvent viscosity and laser wavelength. The effect of alkyl substituents on the ratio of bond cleavages, Ph-Se/total C-Se, was investigated for five alkyl phenyl selenides; the ratio decreased in the order pentyl > 2-methylallyl > allyl > 1-ethylpropyl > tert-butyl groups. The contribution of Ph-Se bond cleavage is most probably the origin of the large deviations in the yields of radical reactions induced by photolyses of 1, which can be minimized by selecting appropriate solvents and wavelength of light.
- Ouchi, Akihiko,Liu, Suyou,Li, Zhong,Kumar, S. Ajaya,Suzuki, Toshiaki,Hyugano, Takeshi,Kitahara, Haruo
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p. 8700 - 8706
(2008/03/12)
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- Palladium-catalyzed desulfinylative Negishi C-C bond forming cross-couplings of sulfonyl and organozinc chlorides
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Arene-, phenylmethane- and alkenesulfonyl chlorides are suitable electrophilic reagents in desulfinylative carbon-carbon bond formation cross-coupling reactions with organozinc reagents.
- Dubbaka, Srinivas Reddy,Vogel, Pierre
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p. 3345 - 3348
(2007/10/03)
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- Mechanism of the diphenyldisulfone-catalyzed isomerization of alkenes. Origin of the chemoselectivity: Experimental and quantum chemistry studies
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Polysulfone- and diphenyldisulfone-catalyzed alkene isomerizations are much faster for 2-alkyl-1-alkenes than for linear, terminal alkenes. The mechanism of these reactions has been investigated experimentally for the isomerization of methylidenecyclopentane into 1-methylcyclopentene, and theoretically [CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) calculations] for the reactions of propene and 2-methylpropene with a methanesulfonyl radical, MeSO 2?. On heating, polysulfones and (PhSO2)2 equilibrate with sulfonyl radicals, RSO2?. The latter abstract allylic hydrogen atoms in one-step processes giving allylic radical/RSO 2H pairs that recombine within the solvent cage producing the corresponding isomerized alkene and RSO2?. The sulfinic acid, RSO2H, can diffuse out from the solvent cage (H/D exchange with MeOD,D2O) and reduce an allyl radical. Calculations did not support other possible mechanisms such as hydrogen exchange between alkenes, electron transfer, or addition/elimination process. Kinetic deuterium isotopic effects measured for the (PhSO2)2-catalyzed isomerization of methylidenecyclopentane and deuterated analogues and calculated for the H abstraction from 2-methylpropene and deuterated analogues by CH 3-SO2? are consistent also with the one-step hydrogen transfer mechanism. The high chemoselectivity for this reaction is not governed by an exothermicity difference but by a difference in ionization energies of the alkenes. Calculations for CH3SO2? + propene and CH3SO2? + 2-methylpropene show a charge transfer of 0.34 and 0.38 electron, respectively, from the alkenes to the sulfonyl radical in the transition states of these hydrogen abstractions.
- Markovic, Dean,Varela-Alvarez, Adrian,Sordo, Jose Angel,Vogel, Pierre
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p. 7782 - 7795
(2007/10/03)
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- Enantioselective synthesis of cyclic amides and amines through Mo-catalyzed asymmetric ring-closing metathesis
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First, an efficient method for the synthesis of optically enriched N-fused bicyclic structures is reported. Through Mo-catalyzed desymmetrization of readily available achiral polyene substrates, 5,6-, 5,7-, and 5,8-bicyclic amides can be synthesized in up to >98% ee. The effects of catalyst structure, olefin substitution, positioning of Lewis basic functional groups and ring size are examined and discussed in detail. In the second phase of investigations, a catalytic asymmetric method for highly enantioselective (up to 97% ee) synthesis of small- and medium-ring unsaturated cyclic amines is reported; optically enriched products bear a secondary amine or a readily removable Cbz or acetamide unit. Regio- and diastereo-selective functionalizations of olefins within the optically enriched amine products have been carried out. Both catalytic asymmetric methods include transformations that lead to the formation of trisubstituted as well as disubstituted cyclic alkenes. The protocols outlined herein afford various cyclic amines of high optical purity; such products are not easily accessed by alternative protocols and can be used in enantioselective total syntheses of biologically active molecules.
- Sattely, Elizabeth S.,Alexander Cortez,Moebius, David C.,Schrock, Richard R.,Hoveyda, Amir H.
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p. 8526 - 8533
(2007/10/03)
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- Organometallic-type reactions in aqueous media. Wurtz-coupling of alkyl halides with manganese/cupric chloride
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Homo-coupling of alkyl halides in aqueous media can be mediated by manganese/cupric chloride to give the dimerisation products in good yield. Cross-coupling can also be controlled to give the desired product.
- Ma, Jihai,Chan, Tak-Hang
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p. 2499 - 2502
(2007/10/03)
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- Infrared and nuclear magnetic resonance spectroscopic studies of the structure and dynamics of allylic magnesium compounds
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The infrared spectra of allyl- and methallyl-d2-magnesium bromides have two double bond stretching bands, corresponding to C=CH2 and C=CD2 groups in equilibrating allylic isomers. The methylene resonances in the 13C NMR spectra of allylmagnesium bromide and chloride and methallylmagnesium bromide are broadened at low temperatures by an exchange process which appears to be the interconversion between the classical unsymmetrical allylic structures. Analogous changes are seen in the spectrum of 1,3-dimethylallylmagnesium chloride and in the proton NMR spectrum of allylmagnesium bromide. Rate constants and activation parameters for the exchange have been determined from the line broadenings. Unlike the Grignard reagent, the methylene resonances of diallylmagnesium in tetrahydrofuran are not significantly broadened at reduced temperature, and the deuterated reagent does not have two distinct double bond stretching bands in the IR spectrum.
- Hill, E. Alexander,Boyd, Winston A.,Desai, Hemnalini,Darki, Amir,Bivens, Lymel
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- - the Wet Chemical Route to a Highly Reactive Titanium Hydride
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The reaction between catalytically prepared magnesium hydride (MgH2*) and in a molar ratio of 1.5:1 in THF yields a highly pyrophoric, X-ray amorphous titanium hydride precipitate with the composition (2).This novel titanium hydride precipitate with the composition (2).This novel titanium hydride has been characterized through hydrolysis and iodolysis, as well as through thermolysis to Ti* and H2 in the solid state and in organic solvents. 2 is slightly soluble in THF and proves itself as an active reagent in a variety of reactions. - Keywords: Magnesium Hydride, Titanium Hydride, McMurry-Reaction, Titanium
- Becker, Beate,Bogdanovic, Borislav
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p. 476 - 482
(2007/10/02)
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- Photoinduced electron-transfer reactions of some 1,4-dialkylbicyclo[2.2.0]hexanes. Generation of cyclohexane-1,4-diyl radical cations in boat form and their stereospecific [σ1s + 2s] cleavage
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The title reactions of exo ando-1,2,3,4,5,6-hexamethyl- and deuterium-labeled l,4-dimethylbicyclo[2.2.0]hexanes 1-3 and of 3,5-dioxatricyclo[5.2.2]undecanes 4 are studied in the presence of a variety of electron acceptor sensitizers. Compound 1 undergoes virtually sensitizer-independent, highly stereospecific [σ1s + 2s] ring cleavage upon one-electron oxidation to give erythro-(E,E)-3,4,5,6-tetramethylocta-2,6-diene as the major product. Similar, but somewhat decreased stereospecificity is also observed in the reaction of 3. The generation of boat cyclohexane-1,4-diyl radical cations undergo the [σ1s + 2s] cleavage while retaining their configurations is proposed. The decreased stereospecificity of the reaction of 3 is attributed to the configurational instability of the resultant diene radical cation rather than to the incomplete stereospecificity of the ring cleavage process. In contrast, the composition of product derived from 2 is highly dependent on the sensitizer used and is found to be correlated with the reduction potential (E1/2red) of the latter. Thus 2 is predominantly isomerized to 1 by the sensitizers whose E1/2reds. are more negative than -0.8 V vs SCE, while it affords primarily hexamethylcyclohexene (5) with the more readily reducible sensitizers. In addition to 1 and/or 5, erythro-(E,Z)-diene 6 is invariably produced as the minor product, but the [σ1s + 2s] cleavage of 2 to give the erythro-(Z,Z)-diene is not detected. The stereochemistry and the sensitizer-dependency of the reaction of 2 are rationalized in terms of rapid ring flip of the incipient boat radical cation into the chair form to relieve steric repulsion among the four endo-methyl substituents. The chair intermediate subsequently rearranges to the radical cations of 5 and 6, in competition with back electron transfer (ET) from the counter radical anion to give Cyclohexane-1,4-diyl diradical, which, in turn, collapses to produce 1 and 6. The rate of the back-ET is dependent on the E1/2red of the sensitizer and so is the product composition. The different stereospecificities of the cleavage reactions of 1 and 2 rule out the operation of a concerted mechanism. The reaction of 4 affords a rearranged isomer as a primary product which is shown by a labeling experiment to be derived via intramolecular proton (or hydrogen) transfer subsequent to the [σ1s + 2s] cycloreversion, thus proving the occurrence of the ring cleavage in the single-electron-transferred radical cation. In accord with the experimental observation, the [σ1s + 2s] cleavage reactions of 1 and 3 are estimated to be slightly exothermic on the basis of available thermochemical data and calculated heats of formation. This is in marked contrast to the theoretically predicted and experimentally proved high endothermicity of the process in the parent system.
- Tsuji, Takashi,Miura, Toshimasa,Sugiura, Kenichi,Matsumoto, Yoshiyuki,Nishida, Shinya
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p. 482 - 493
(2007/10/02)
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- Deazetation of 1,4-Dimethyl-2,3-diazabicyclooct-2-ene: Stereochemistry and the Formation of Dimethylcyclohexene
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Irradiation of stereospecifically labelled 2H2>-1,4-dimethyl-2,3-diazabicyclooct-2-ene gave 1,4-dimethylbicyclohexane and 2,5-dimethylhexa-1,5-diene with the label randomly distributed between the stereochemically differentiated positions, together with 1,4-dimethylcyclohexene, which was only formed in the direct photolysis.
- Edmunds, Andrew J. F.,Samuel, Christopher J.
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p. 457 - 460
(2007/10/02)
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- The Heat of Formation of the Allyl and Methallyl Radical
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The decomposition of 1,5-hexadiene (1), 2-methyl-1,5-hexadiene (7), and 2,5-dimethyl-1,5-hexadiene into allyl- (2) and methallyl radicals (6) was studied by means of the shoke tube technique with and without oxygen as scavenger.From these data and from the temperature dependence of the equilibria 1 2 and 5 6, measured between 600 and 800 deg C, the heat of formation of the allyl (2) and methallyl radical (6) as well as the activation parameters for the recombination and disproportionation of these radicals have been deduced.
- Roth, Wolfgang R.,Bauer, Frank,Beitat, Arndt,Ebbrecht, Thomas,Wuestefeld, Michael
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p. 1453 - 1460
(2007/10/02)
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- Homolytic Reactions of Ligated Boranes. Part 14. ESR Studies of Ring Opening of Cycloalkylaminyl-Borane Radicals and Reactions of Aminyl-Borane Radicals with Silicon-containing Compounds
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ESR spectroscopy has been used to characterise reactions of the aminyl-borane radicals RN.H->BH3 (2) in solution.The relative rates of β-hydrogen-atom transfer from s, ButC(H)Me, or But> to 2,3-dimethylbut-2-ene and to furan depend on the nature of the group R, confirming that H-atom transfer is bimolecular and does not involve prior β-scission of (2) to give a free hydrogen atom.Because of favourable polar factors, β-H-atom transfer from (2) to the allylsilanes Me3SiCH2CH=CH2 and Me3SiCH2CMe=CH2 are particularly rapid.The cycloalkylaminyl-borane radicals (2; R=cyclo-C3H5 or cyclo-C4H7) undergo rapid ring opening at 282 K, while no spectroscopic evidence was found for opening of the cyclopentyl or cyclohexyl analogues.Alkylaminyl-borane radicals transfer a β-hydrogen atom to hexamethyldisilane to bring about homolytic Si-Si bond cleavage.These radicals also react with trialkylsilanes R3SiH to give R3Si. .Approximate absolute rate coefficients for the reactions of (2) have been determined at 282 or 292 K.Of the primary amine-boranes investigated, s-butylamine- and cyclopentylamine-boranes appear to be the most suitable complexes for ESR spectroscopic work in liquid solution.
- Johnson, Karen M.,Kirwan, J. Nicholas,Roberts, Brian P.
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p. 1125 - 1132
(2007/10/02)
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- An Efficient Electrochemical Coupling of Allylic Halides by Using a Copper Anode
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A new electrolytic method for an efficient coupling of allylic halides by the use of a copper anode and a platinum cathode in the precence of sodium iodide is described.A method which avoids a loss of the copper anode owing to dissolution is also described.
- Tokuda, Masao,Endate, Kazuhiro,Suginome, Hiroshi
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p. 945 - 948
(2007/10/02)
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- STUDIES ON THE CHEMISTRY OF DIOLS AND CYCLIC ETHERS-52. MECHANISM AND STEREOCHEMISTRY OF DEHYDRATION OF OXOLANES TO DIENES
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On γ-Al2O3, BPO4 and NaX zeolite, the dehydration of (+/-)-2,2,3,4,5,5-hexamethyloxolane (2) in the vapour phase leads to the formation of 2,3,4,5-tetramethyl-1,5-hexadiene (8) in a slow process, while meso-2,2,3,4,5,5-hexamethyloxolane (3) is converted to 2,3,4,5-tetramethyl-2,4-hexadiene (7) with high selectivity in a fast reaction.These differences in reaction rate and selectivity indicate that the dehydration of 2 takes place by an E2 mechanism.In contrast, the steric strain in 3 results in ring opening by an E1 mechanism.These conclusions are supported by the nonselective transformations of 2,2,5,5-tetramethyloxolane (1) and 2,2,6,6-tetramethyloxane (4), and the dehydration of 1, 2 and 3 in the presence of formic acid in the liquid phase.The experimental observation prove that both the reactivity and the reaction directions in the dehydration of stereoisomeric oxolanes are determined by steric factors.
- Molnar, Arpad,Bartok, Mihaly
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p. 131 - 142
(2007/10/02)
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- SPECIFIC ALLYLIC-ALLYLIC COUPLING PROCEDURES EFFECTED BY LIGAND-INDUCED ELIMINATION FROM DI(ALLYLIC)PALLADIUM SPECIES
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Bis(allylic)palladium complexes can be induced to undergo reductive elimination by replacement of phosphine ligands in the system with ?-acidic ligands.The product 1,5-dienes, formed in high yield, are predominantly the 'head-to-head' coupled isomers.The bis(allylic)palladium intermediates may be formed by addition of an allylic Grignard or trialkyl(allylic)tin reagent to an(η3-allyl)palladium chloride complex, or by 1,3-diene condensation.The latter process leads to cyclodimerization, 'unusual' for palladium catalysed reactions.
- Goliaszewski, Alan,Schwartz, Jeffrey
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p. 5779 - 5790
(2007/10/02)
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- Photolysis of Reluctant Azoalkanes. Effect of Structure on Photochemical Loss of Nitrogen from 2,3-Diazabicyclooct-2-ene Derivatives
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Azoalkanes containing the bicycloskeleton often prove to be remarkable stable toward loss of nitrogen.These derivatives of 2,3-diazabicyclooct-2-ene (DBO) also exhibit fluorescence whose lifetime extends to 600 ns.This paper is an attempt to understand the effect of fused rings and bridgehead substituents on the photochemical and photophysical properties of DBO.The main factor controlling quantum yields of nitrogen is a 6-11 kcal mol-1 activation barrier that differs for the singlet and triplet states and that seems to mimic the barrier to ground-state deazatization.The product distribution for DBO derivatives is rationalized on the basis of interconverting singlet 1,4-biradicaloids.
- Engel, Paul S.,Horsey, Douglas W.,Keys, Dalen E.,Nalepa, Christopher J.,Soltero, Luis R.
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p. 7108 - 7114
(2007/10/02)
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- Thermolysis of Azoalkanes Containing the 2,3-Diazabicyclooct-2-ene (DBO) Skeleton
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The effect of one and two bridgehead substituents on the thermal stability of DBO is assessed by monitoring the disappearance of four new compounds (8-11).Two cyclopropyl groups are found to lower ΔG for thermolysis by twice the amount of one such group; however, a second bridgehead phenyl substituent is much less effective than the first.Comparison of these results with those of the previously studied methyl and vinyl DBO suggests two mechanisms that are indistinguishable on the basis of available data.In the first one, symmetrical azoalkanes decompose by simultaneous scission of both C-N bonds while unsymmetrical azolakanes exhibit greater breaking of the C-N bond at the transition state.This idea is described in a More O'Ferrall-Jencks-Thornton diagram.The second possible mechanism is reversible cleavage of a weaker C-N bond followed by loss of nitrogen from an intermediate diazenyl radical.Incorporation of endocyclic fused rings into the DBO skeleton generally slow down thermolysis, perhaps by inhibiting planarization of the carbon atoms α to the azo group.
- Engel, Paul S.,Nalepa, Christopher J.,Horsey, Douglas W.,Keys, Dalen E.,Grow, Robert T.
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p. 7102 - 7107
(2007/10/02)
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- Reactions of Allylic Grignard Reagents and Unsaturated Amines
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Reactions were studied of allylic Grignard reagents with allylic and propargylic amines.Additions were observed to N-allylaniline (1), cinnamylamine (6), N,N-dimethylcinnamylamine (10), and 3-(dimethylamino)-1-phenyl-1-propyne (12) but not to allylamine, diallylamine, N-allyl-N-methylaniline, N,N-dimethylallylamine, or N,N-diethylallylamine.Reactions of 3-amino-1-phenyl-1-propyne (8) furnished phenylacetylene rather than an addition product.By comparing reactivities of the amines and comparablehydrocarbons, it is concluded that tertiary amino functions and metalated primary and secondary amino functions can assist Grignard reagent additions to alkene and alkyne functions.Comparisons of reactivities of theunsaturated amines and comparable alcohols suggest that assistance by a metalated amino function is less effective than by a metalated hydroxyl function but more effective than by a tertiary amino function.Another comparison suggests that a metalated phenylamino group is more effective than a metalated primary amino group.
- Richey, Herman G.,Moses, L. Meredith,Domalski, M.S.,Erickson, Wayne F.,Heyn, Alan S.
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p. 3773 - 3780
(2007/10/02)
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- Studies on the Conversions of Diols and Cyclic Ethers. Dehydration of Alcohols and Diols on the Action of Dimethylsulfoxide
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The transformations of 13 alcohols and 13 diols in the presence of a small amount dimethylsulfoxide (1/16 mol) were studied.Relationships were found between the type of the hydroxy compound and the selectivity of the transformation, and conclusions were drawn regarding the transformation mechanism.The ether formation observed with certain alcohols proceeds via a carbenium cation.The reaction conditions applied were found suitable for including water elimination from the ditertiary 1,2- and 1,3-diols (pinacol rearrangement, 1,2-elimination).From the 1,4- and 1,5-diols the corresponding oxacycloalkanes can be obtained in good yield.Cyclodehydration occurs by intramolecular nucleophilic substitution, via a concerted mechanism.The effect of DMSO is excerted directly, and proton-catalysis occurs simultaneously.
- Molnar, Arpad,Bartok, Mihaly
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p. 389 - 398
(2007/10/02)
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