- Microwave Spectroscopy of Isotopic Cyclobutene Ozonide as a Means of Quantification of Ozone Isotopomers
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The microwave spectrum of cyclobutene ozonide, a new isotopomeric species, has been assigned and the absolute direction of the dipole moment has been determined. The aim of this investigation has been to determine symmetric/asymmetric isotopomer concentrations in an arbitrary 18O-substituted ozone isotopomer mixture. The method we have used consists of transforming the ozone into cyclobutene ozonide and using intensities of rotational lines of these to quantify the composition of the original ozone isotopomer mixture. Such a method has been accomplished; unfortunately propagation of errors renders it difficult to obtain results of high accuracy.
- Larsen, Niels Wessel,Pedersen, Thorvald
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- THE MICROWAVE SPECTRUM, STRUCTURE AND DIPOLE MOMENT OF CYCLOBUTENE OZONIDE (2,3,7-TRIOXABICYCLOHEPTANE)
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cyclobutene ozonide containing deuterium, 13C and 18O enrichment was prepared by ozonolysis of cyclobutene and via singlet molecular oxygen addition to furan.It was established that the ozonide has Cs symmetry.The structure was determined from the assignment of the microwave spectra of eight isotopic species.The peroxy bond distance of 1.492(5) Angstroem is increased by about 0.03 Angstroem compared with less strained monocyclic ozonides.The ring strain is also evident in several other bond distances and angles when compared with cyclopentene ozonide.The dipole moment is 2.857(2) debye.
- Borseth, Donald G.,Lorencak, Primoz,Badawi, Hassan M.,Hillig II, Kurt W.,Kuczkowski, R. L.,Mendenhall, G. David
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- Fluoroalkyl-Containing 1,2-Disubstituted Cyclobutanes: Advanced Building Blocks for Medicinal Chemistry
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Synthesis of previously unavailable 1,2-disubstituted cyclobutane building blocks bearing mono-, di- and trifluoromethyl groups are disclosed. The key steps included deoxofluorination or TMAF-mediated nucleophilic substitution in the appropriate bifunctional cyclobutanes; for the CF3-substituted derivatives, alternative methods based on cyano- or azidotrifluoromethylation of cyclobutene using the Togni reagent II were also proposed. All methods provided trans diastereomers of the target primary amines and carboxylic acids (6 representatives) and were suitable for their multigram preparation. Furthermore, dissociation constants (pKa) and lipophilicity (logP) values were measured to evaluate the effect of the fluoroalkyl substituents on acidity/basicity and lipophilicity of the building blocks obtained.
- Demchuk, Oleksandr P.,Hryshchuk, Oleksandr V.,Vashchenko, Bohdan V.,Trofymchuk, Serhii A.,Melnykov, Kostiantyn P.,Skreminskiy, Artem,Volochnyuk, Dmitriy M.,Grygorenko, Oleksandr O.
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- Lessons in Strain and Stability: Enantioselective Synthesis of (+)-[5]-Ladderanoic Acid
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The synthesis of structurally complex and highly strained natural products provides unique challenges and unexpected opportunities for the development of new reactions and strategies. Herein, the synthesis of (+)-[5]-ladderanoic acid is reported. En route to the target, unusual and unexpected strain release driven transformations were uncovered. This occurrence required a drastic revision of the synthetic design that ultimately led to the development of a novel stepwise cyclobutane assembly by an allylboration/Zweifel olefination sequence.
- Hancock, Erin N.,Kuker, Erin L.,Tantillo, Dean J.,Brown, M. Kevin
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supporting information
p. 436 - 441
(2019/11/25)
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- The cyclopropylcarbinyl route to γ-silyl carbocations
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The mesylate derivative of cis-1-hydroxymethyl-2-trimethylsilylcyclopropane has been prepared, along with a number of related mesylates and triflates with substituents on the 1-position. These substrates all solvolyze in CD3CO2D to give products derived from cyclopropylcarbinyl cations that undergo further rearrangement to give 3-trimethylsilylcyclobutyl cations. These 3-trimethylsilylcyclobutyl cations are stabilized by a long-range rear lobe interaction with the γ-trimethylsilyl group. When the substituent is electron-withdrawing (CF3, CN, or CO2CH3), significant amounts of bicyclobutane products are formed. The bicyclobutanes are a result of γ-trimethylsilyl elimination from the cationic intermediate that has an unusually long calculated Si-C bond. The solvolysis chemistry of mesylate and triflate derivatives of trans-1-hydroxymethyl-2-trimethylsilylcyclopropane and 1-substituted analogs can be quite different since these substrates do not generally lead to 3-trimethylsilylcyclobutyl cations.
- Creary, Xavier
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supporting information
p. 1769 - 1780
(2019/08/07)
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- A Diverted Aerobic Heck Reaction Enables Selective 1,3-Diene and 1,3,5-Triene Synthesis through C-C Bond Scission
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Substituted 1,3-dienes are valuable synthetic intermediates used in myriad catalytic transformations, yet modern catalytic methods for their preparation in a highly modular fashion using simple precursors are relatively few. We report here an aerobic boron Heck reaction with cyclobutene that forms exclusively linear 1-aryl-1,3-dienes using (hetero)arylboronic acids, or 1,3,5-trienes using alkenylboronic acids, rather than typical Heck products (i.e., substituted cyclobutenes). Experimental and computational mechanistic data support a pericyclic mechanism for C-C bond cleavage that enables the cycloalkene to circumvent established limitations associated with diene reagents in Heck-type reactions.
- McAlpine, Neil J.,Wang, Long,Carrow, Brad P.
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supporting information
p. 13634 - 13639
(2018/10/24)
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- Formal (4+1) cycloaddition of methylenecyclopropanes with 7-aryl-1,3,5-cycloheptatrienes by triple gold(I) catalysis
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7-Aryl-1,3,5-cycloheptatrienes react intermolecularly with methylenecyclopropanes in a triple gold(I)-catalyzed reaction to form cyclopentenes. The same formal (4+1) cycloaddition occurs with cyclobutenes. Other precursors of gold(I) carbenes can also be used as the C1 component of the cycloaddition.
- Wang, Yahui,Muratore, Michael E.,Rong, Zhouting,Echavarren, Antonio M.
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supporting information
p. 14022 - 14026
(2015/02/19)
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- Accuracy of calculations of heats of reduction/hydrogenation: Application to some small ring systems
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The enthalpies of reduction of carbonyl compounds and hydrogenation of alkenes have been calculated at the HF, B3LYP, M06, MP2, G3, G4, CBS-QB3, CBS-APNO, and W1BD levels and, in the case of the first four methods, using a variety of basis sets up to aug-cc-pVTZ. The results are compared with the available experimental data, and it is found that the compound methods are generally more satisfactory than the others. Large basis sets are usually needed in order to reproduce experiments. Some C-C bond hydrogenolysis reactions also have been examined including those of bicycloalkanes and propellanes. In addition, the dimerization of the remarkably strained bicyclo[2.2.0]hex(1,4)ene was studied. The reaction forming a pentacyclic propellane was calculated to have ΔH = -57 kcal/mol, and the cleavage of the propellane to give a diene had ΔH = -71 kcal/mol. The strain energies of these compounds were estimated.
- Wiberg, Kenneth B.
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p. 10393 - 10398
(2013/01/15)
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- γ-silyl cyclobutyl carbocations
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(Graph Presented) A series of 3-trimethylsilyl-1-substituted cyclobutyl trifluoroacetates have been prepared and reacted in CD3CO 2D. Rate data indicate that the substrates with the trimethylsilyl group cis to the leaving group react with assistance due to γ-silyl participation. Rate enhancements range from a factor of 209 for α-phenyl-substituted cations to 4.6 × 104 for α-methyl-substituted cations to >1010 for the unsubstituted γ-trimethylsilylcyclobutyl cation. Acetate substitution products are formed with net retention of stereochemistry. These experimental studies, as well as B3LYP/6-31G* computational studies, are consistent with the involvement of carbocations where the rear lobe of the γ-Si-C bond interacts strongly with the developing cationic center. Solvolytic rate studies, as well as computational studies, suggest that the secondary γ-trimethylsilylcyclobutyl cation is even more stable than the β-trimethylsilylcyclobutyl cation, i.e., the γ-silyl effect actually outweighs the potent β-silyl effect. Although computational studies suggest the existence of certain isomeric cations, where the front lobe of the Si-C bond interacts with the cationic center, solvolytic evidence for the involvement of these front lobe stabilized cations is less compelling.
- Creary, Xavier,Kochly, Elizabeth D.
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supporting information; experimental part
p. 9044 - 9053
(2010/03/04)
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- Enantioselective synthesis of pentacycloanammoxic acid
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A highly effective enantioselective synthesis of pentacycloanammoxic acid (1), an unusual naturally occurring fatty acid from Candidatus Brocadia anammoxidans, has been accomplished. The C20-structure of 1 was assembled with stereocontrol from four building blocks, cyclobutene, 2-cyclopentenone, the chiral silylcyclopentenone 6, and 7-bromoheptanoic acid. Both 1 and its enantiomer are now available in quantities that should facilitate future studies on the mode of biosynthesis which appears to be unprecedented. Copyright
- Mascitti, Vincent,Corey
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p. 3118 - 3119
(2007/10/03)
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- Experimental determination of the heat of hydrogenation of phenylcyclobutadiene
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The heat of hydrogenation of phenylcyclobutadiene (ΔH° hyd = 57.4 ± 4.9 kcal mol-1) was determined via a thermodynamic cycle by carrying out gas-phase measurements on 1-phenylcyclobuten-3-yl cation. This leads to an antiaromatic destabilization energy of 27 ± 5 kcal mol-1, a difference of 9.6 ± 4.9 kcal mol-1 for the first and second C-H bond dissociation energies of 1-phenylcyclobutene, and an estimate of 96 ± 5 kcal mol-1 for the heat of formation of cyclobutadiene. These results are compared to G3, G3(MP2), and B3LYP computations and represent the first experimental measurements of the energy of a monocyclic cyclobutadiene.
- Fattahi, Alireza,Lis, Lev,Kass, Steven R.
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p. 13065 - 13069
(2007/10/03)
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- β-hydride elimination from alkyl and cycloalkyl groups on a Cu(100) surface: Ring strain and planarity of the transition state
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Alkyl (C5-C6), cycloalkyl (C4-C7), and 2-bicyclo[2.2.1]heptyl (norbornyl) groups have been generated on a Cu(100) surface by the dissociative adsorption of their bromo derivatives. All these groups decompose by a β-hydride elimination reaction upon heating the surface, and the product alkenes which are evolved from the surface were detected by mass spectrometry. Studies in which cyclohexyl-d1 groups were generated on the surface by reacting D atoms with physisorbed cyclohexene show that the coadsorbed bromine atoms in the bromoalkane studies do not have a significant effect on the rate or mechanism of these reactions. A particularly interesting finding from these studies is that the rates of β-hydride elimination for these structurally similar alkyl groups vary by 6-7 orders of magnitude if one extrapolates the rates to a common reaction temperature of 200 K. Assuming a common, firstorder preexponential factor of 1013 s-1 gives the following relative rate scale (normalized to 1 for the transformation cyclohexyl → cyclohexene): cyclobutyl (0.6) 4) ≈ 3-pentyl (5 × 104) 6). Thermodynamic differences between these reactions, as qualitatively addressed by differences in strain energy between reactant and product, may play a role in the 20-fold difference in rate between cyclopentyl and 3-pentyl, but thermodynamics cannot account for the ~4 order of magnitude larger rate for 3-hexyl relative to cyclohexyl. We suggest that the dramatic rate difference between these two secondary alkyls is due to the different free energy changes required to achieve a planar geometry in the transition state, i.e., a dihedral angle of 0° between the substituents on α- and β-carbons.
- Teplyakov, Andrew V.,Bent, Brian E.
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p. 10076 - 10087
(2007/10/03)
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- Dynamic models for the thermal deazetization of 2,3-diazabicyclo[2.2.1]hept-2-ene
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Kinetic studies on the thermal nitrogen extrusion from 2,3-diazabicyclo[2.2.1]hept-2-ene-exo,exo-5,6-d2 are reported. The ratio of rate constants for formation of the label-isomeric products (bicyclo[2.1.0]pentane-exo,exo-2,3-d2 and -endo,endo-2,3-d2) is found to exhibit no statistically significant temperature dependence. A comparison of gas-phase and solution-phase results is presented. The results are interpreted in terms of two complementary dynamic models. In the first, classical trajectory calculations are run on a three-dimensional projection (two geometric coordinates) of the potential energy hypersurface. These calculations correctly identify the major product, and reproduce the near temperature-independence of the rate-constant ratio, but do not match the ratio quantitatively. Modification of the trajectory calculations to simulate the effect of collisions with solvent molecules also qualitatively matches the observed difference between gas-phase and solution-phase behavior. In the second model, the vector of atomic displacements corresponding to the reaction coordinate at the transition state for nitrogen loss is identified by both semiempirical and ab initio calculations. The components of this vector pointing along the paths to the post-transition-state minima are computed and are shown to lead to a prediction of the product ratio that is in good (if partly fortuitous) agreement with the experimental result. The vector model is used to predict isotope effects on the product ratio, which are then investigated experimantally with 2,3-diazabicyclo[2.2.1]hept-2-ene-endo,endo-1,4,5,6,7,7-d6 and -endo-7-d.
- Lyons, Barbara A.,Pfeifer, J?rg,Peterson, Thomas H.,Carpenter, Barry K.
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p. 2427 - 2437
(2007/10/02)
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- Ring-Formation from Allyl- and Vinylstannanes Initiated by Treatment with Butyl-Lithium
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The allylstannane 1 and the vinylstannane 3, 5 and 7 cyclise when treated with butyl-lithium.
- Barbero, Asuncion,Cuadrado, Purificacion,Gonzalez, Ana M.,Pulido, Francisco J.,Rubio, Rosa,Fleming, Ian
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p. 5841 - 5842
(2007/10/02)
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- Experimental and Computational Evidence Indicating That the Initial Carbene Conformation Is Product Determining in the Reactions of Cyclopropylmethylene
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The decomposition of cyclopropyldiazomethane, 2, to generate cyclopropylmethylene, 1, was carried out from 573 to 773 K under flash vacuum pyrolysis (FVP) conditions and from 77 to 303 K photolytically in hydrocarbon solvents.An examination of the ratio of ring-expanded products (RE, butadiene and cyclobutene) to those of cleavage (C, ethylene and acetylene) as a function of temperature leads to the conclusion that RE is favored over C by 2.3 kcal/mol in the FVP of 2.Ab initio calculations (MP2/6-31G*//3-21G) predict that decomposition of 2 to give the conformer of 1in which the ring methyne hydrogen and the α-hydrogen are cis (1a) is more favorable than formation of the trans conformer (1b) by 1.1 kcal/mol.The calculated activation parameters for the formation of 1a and 1b have been combined with those calculated previously for the reactions of 1a and 1b, which indicate the RE is favored from 1a while 1b gives C, to give theoretical values of RE:C as a function of temperature which lead to a computed difference in Ea between RE and C of 2.7 kcal/mol, in good agreement with the 2.3 kcal observed experimentally.Photolysis of 2 gives a higher ratio of C to RE than does FVP.This may be a consequence of the fact that a more energetic carbene is produced in the photolysis than in the thermolysis.
- Chou, Jun-Hong,McKee, Michael L.,Felippis, James De,Squillacote, Michael,Shevlin, Philip B.
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p. 3291 - 3295
(2007/10/02)
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- In Situ Fourier Transform Infrared Study of Crotyl Alcohol, Maleic Acid, Crotonic Acid, and Maleic Anhydride Oxidation on a V-P-O industrial Catalyst
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Crotyl alcohol, maleic acid, crotonic(2-butenoic) acid, and maleic anhydride were fed to an in situ infrared cell at 300 deg C containing a P/V = 1.1 vanadium-phosphorus-oxide (V-P-O) catalyst used for the selective oxidation of n-butane.Crotyl alcohol was used as a mechanistic probe for the formation of reactive olefin species observed during previous n-butane and 1-butene studies.Crotonic acid, maleic acid, and maleic anhydride were fed as probes for the existence of other possible adsorbed intermediates.Olefin species and maleic acid are proposed as possible reaction intermediates in n-butane selective oxidation to maleic anhydride.The involvement of peroxide species in the oxidation of butadiene to maleic acid is also discussed.
- Wenig, Robert W.,Schrader, Glenn L.
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p. 5674 - 5680
(2007/10/02)
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- A STUDY OF THE NORRISH TYPE II REACTION IN THE SOLID STATE
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The solid state photochemistry of six α-cycloalkyl-p-chloroacetophenone derivatives (cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, exo-2-norbornyl and 1-adamantyl) is reported.All six undergo smooth type II photochemistry in the crystalline phase.The cyclization-to-cleavage ratios and the cis-to-trans cyclobutanol ratios are tabulated for each ketone, and the results are compared with the corresponding data from the solution photolyses.In general, the solid state medium was found to exert a relatively small effect on the product ratios.The γ-hydrogen atom to carbonyl oxygen abstraction distances, as well as the angular relationships between these two atoms, were determined from the X-ray crystal structure data for each ketone.The data showed that (1) six atom abstraction geometries other than chairlike can be accommodated, (2) abstraction can occur over distances much longer than previously supposed (up to 3.10 Angstroem), and (3) there is no strict requirement that the hydrogen undergoing abstraction be in the plane of the carbonyl oxygen n-orbital.Attempts were made to correlate the solid state structural data with the rate constants for hydrogen atom abstraction as determined in solution from Stern-Volmer quenching plots.The lack of any such correlation is interpreted as indicating a significant contribution to reaction in solution from non-minimum energy ketone conformations.
- Scheffer, John R.,Trotter, James,Omkaram, Nalamasu,Evans, Stephen V.,Ariel, Sara
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p. 169 - 196
(2007/10/02)
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- 1,2-DIMETHYLSPIROHEX-1-ENE BY ADDITION OF CYCLOBUTYLIDENE TO 2-BUTYNE
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The first addition of a cyclobutylidene (carbenoid) to an alkyne is reported.By C4+C2-coupling the spirohex-1-ene system 8 is constructed.Furthermore, cyclobutylidene adds to methylenecyclopropane, its intramolecular reaction product, to give the novel dispirooctane 11.
- Brinker, Udo H.,Weber, Juergen
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p. 5371 - 5374
(2007/10/02)
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- 185-nm Photochemistry of Cyclobutene and Bicyclobutane
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The high quantum yield of the direct 185-nm photolysis of cyclobutene (φs=0.71) leading to 1,3-butadiene is in accord with symmetry-allowed electrocyclic ring opening of a ?,?*-excited singlet state of cyclobutene.The formation of ethene, acetylene, and methylenecyclopropane as minor products presumably involves cyclopropylmethylene and cyclobutylidene as carbene intermediates, formed on (?,3s)-Rydberg excitation of cyclobutene.The 185-nm photolysis of bicyclobutane resembles that of the homologous bicycloalkanes.As main products cyclobutene (φp=0.30) and 1,3-butadiene (φp=0.29) are formed.On the other hand, the transformations of methylenecyclopropane on 185-nm irradiation, leading to ethene, acetylene, and 1,3-butadiene, are akin to radiolysis and gas-phase photolysis results of this substrate.
- Adam, Waldemar,Oppenlaender, Thomas,Zang, Gerald
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p. 3921 - 3924
(2007/10/02)
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- Bicyclopentanone. Synthesis, Thermal Chemistry, and Photochemistry
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Bicyclopentanone (1) has been prepared in two steps, the key reaction being the ozonolysis of 2-phenylbicyclopentan-2-ol (6).On heating, 1 undergoes cycloreversion to allylketene (13).The activation parameters and solvent effects for this process suggest that the reaction is concerted and that the transition state is relatively nonpolar.The predominant photochemical pathway for 1 is decarbonylation to bicyclobutane (16).Cycloreversion to 13 is a minor reaction mode.Both the thermal and photochemical results are rationalized by considering the high strain energy and novel geometrical features of 1, and, in the latter case, the unusually high energy of its 1(n?excit.) state.
- Sponsler, Michael B.,Dougherty, Dennis A.
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p. 4978 - 4984
(2007/10/02)
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- Homolytic Ring Fission reactions of Bicycloalkanes and Bicycloalk-2-yl Radicals: Electron Spin Resonance Study of Cycloalkenylmethyl Radicals
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Hydrogen abstraction from bicycloalkanes (n=3-6) by t-butoxyl radicals was examined by an e.s.r. technique.The main site of attack was C(2) giving bicycloalk-2-yl radicals which rearranged by β-scission of the outer cyclopropane bonds to give cycloalkenylmethyl radicals.This is in contrast to the bicycloalk-2-yl radicals (n=1,2) which rearranged by fission of the inter-ring bonds to give cycloalkenyl radicals. β-Scission in bicycloalk-2-yl radicals was examined by semi-empirical SCF MO calculations.The conformations and barriers to internal rotation of the cycloalkenylmethyl radicals were determined from the variation in the β-H hyperfine splitting constants with temperature.Photobromination of bicycloalkanes (n=3,4) was also investigated in CCl4 solution.The main process was bimolecular homolytic substitution (SH2) by bromine atoms at the cyclopropane carbons, but there was an increase in hydrogen abstraction with ring size.The SH2 reactions parallel the β-scission reactions of the bicycloalk-2-yl radicals in that the main bond undergoing fission changes from the inter-ring bond to the outer cyclopropane bond as the ring size increases.
- Roberts, Charles,Walton, John C.
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p. 879 - 886
(2007/10/02)
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- SMALL RING COMPOUNDS-XLI. CYCLOBUTENE CYCLOADDITIONS; SYNTHESIS AND REACTIVITY IN THE BICYCLOHEXAN-2-ONE SERIES
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Cyclobutene, prepared by base-induced elimination from tosyloxycyclobutane 19 undergoes cycloaddition with ethyl propiolate in the presence of AlCl3 to provide ethyl bicyclohex-2-ene-2-carboxylate 20.This cycloadduct at room temperature and in the presence of AlCl3 undergoes forbidden ring opening into ethyl cyclohexa-1,3-diene-2-carboxylate 21.The cycloaddition of cyclobutene with dichloroketene provides 3,3-dichlorobicyclohexan-2-one 24 and after reductive halogen removal the endo 3-chloro bicyclohexan-2-one 28 (the first study of this strained system).However, further dechlorination of 28 results in rearrangement and fragmentation reactions.
- Fadel, A.,Salauen, J.,Conia, J. M.
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p. 1567 - 1574
(2007/10/02)
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- Cyclobutylidenes from Geminal Dihalogenocyclobutanes
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Cyclobutylidene, or a related carbenoid, can be generated by reaction of geminal dibromocyclobutane with methyl-lithium at temperatures as low as -78 deg C to yield methylenecyclopropane and cyclobutene nearly quantitatively.
- Brinker, Udo H.,Schenker, Gilbert
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p. 679 - 681
(2007/10/02)
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- The thermal and photochemical decomposition of cis-1,2-cyclobutanedicarboxylic anhydride in the vapour phase
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The thermal decomposition of cis-1,2-cyclobutanedicarboxylic anhydride (CBA) has been studied in a static system in the range 625-725 K.The major process observed was a homogeneous unimolecular decomposition to form ethylene and maleic anhydride, with first order rate parameters A = 1.14(+/-0.1) x 1014 s-1 and E = 55.1+/-1 kcal/mol.A very minor decomposition channel yielding butadiene, CO2, and CO was also observed, with A = 8.4(+/-0.1) x 1014 s-1 and E = 67.5+/-1 kcal/mol.The decomposition induced by a pulsed CO2 laser was also studied briefly; the same two decomposition channels were observed and their dependence on fluence and pressure examined.The ultraviolet photolysis of CBA was also investigated between 210 and 365 nm.In addition to the products found in the thermal reaction, cyclobutene was also the a major product, and product ratios were measured as a function of wavelenght and added CO2.Mechanisms in the three systems are discussed and compared.
- Back, R. A.,Parsons, J. M.
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p. 2692 - 2696
(2007/10/02)
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