- New stereoselective Csp2-Csp3 coupling: Catalytic iodomethylation of acetylene with methyl iodide into E-1-iodopropene
-
The catalytic addition of methyl iodide to acetylene yielding E-1-iodopropene has been discovered. The reaction competes with the formation of E,E-1,4-diiodobuta-1,3-diene. The key intermediate in these reactions is the methylvinyl derivative of PtIV
- Mitchenko,Khazipov,Krasnyakova
-
p. 304 - 310
(2014/07/21)
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- Supported imidazolylphosphine catalysts for highly (E)-selective alkene isomerization
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For fine chemical synthesis, immobilized catalysts offer little advantage if they produce a product mixture that must be separated. Selective isomerization of terminal olefins is achieved by heterogenized bifunctional catalysts. Outstanding and consistent (E)-selectivity (>99%) even in cases where (E) and (Z) isomers are of comparable stability, combined with modest catalyst loadings (1 to 2 mol %), set these catalysts apart from previously reported systems. Ease of catalyst removal and high geometric selectivity avoid tedious purifications.
- Erdogan, Gulin,Grotjahn, Douglas B.
-
supporting information
p. 2818 - 2821
(2014/06/23)
-
- Applications of PC(sp3)P iridium complexes in transfer dehydrogenation of alkanes
-
Iridium ethylene complexes based on the PC(sp3)P pincer-type triptycene ligand have been synthesized. Complexes bearing various substituents on the phosphines have been investigated as catalysts in transfer dehydrogenation of alkanes. The complex 8a, which bears isopropyl groups, has demonstrated high stability and activity when used as a catalyst in the disproportionation of 1-hexene at 180 °C and in the transfer dehydrogenation of linear and cyclic alkanes with tert-butylethylene as a hydrogen acceptor at 200°C. A similar complex bearing a CH2NMe2 group, 33, allowed support of the catalyst on γ-alumina for operation in a heterogeneous mode.
- Bzier, David,Brookhart, Maurice
-
p. 3411 - 3420
(2015/02/19)
-
- Platinum-catalyzed addition of iodomethane to acetylene
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The reaction of iodomethane and acetylene in the presence of Pt II and NaI in acetone gives (E)-1-iodopropene. A possible mechanism involves the intermediate formation of a PtIV methyl vinyl derivative by the iodoplatination of acetylene with a reversibly formed a PtIV methyl complex and assumes the catalytic character of the process.
- Mitchenko,Khazipov,Krasnyakova
-
p. 984 - 988
(2014/03/21)
-
- Synthesis of p-xylene from ethylene
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As oil supplies dwindle, there is a growing need to develop new routes to chemical intermediates that utilize alternative feedstocks. We report here a synthesis of para-xylene, one of the highest volume chemicals derived from petroleum, using only ethylene as a feedstock. Ethylene is an attractive alternative feedstock, as it can be derived from renewable biomass resources or harnessed from large domestic shale gas deposits. The synthesis relies on the conversion of hexene (from trimerization of ethylene) to 2,4-hexadiene followed by a Diels-Alder reaction with ethylene to form 3,6-dimethylcyclohexene. This monoene is readily dehydrogenated to para-xylene uncontaminated by the ortho and meta isomers. We report here a selective synthesis of para-xylene, uncontaminated by the ortho or meta isomers, using ethylene as the sole feedstock.
- Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
-
supporting information
p. 15708 - 15711,4
(2012/12/11)
-
- Synthesis of p-xylene from ethylene
-
As oil supplies dwindle, there is a growing need to develop new routes to chemical intermediates that utilize alternative feedstocks. We report here a synthesis of para-xylene, one of the highest volume chemicals derived from petroleum, using only ethylene as a feedstock. Ethylene is an attractive alternative feedstock, as it can be derived from renewable biomass resources or harnessed from large domestic shale gas deposits. The synthesis relies on the conversion of hexene (from trimerization of ethylene) to 2,4-hexadiene followed by a Diels-Alder reaction with ethylene to form 3,6-dimethylcyclohexene. This monoene is readily dehydrogenated to para-xylene uncontaminated by the ortho and meta isomers. We report here a selective synthesis of para-xylene, uncontaminated by the ortho or meta isomers, using ethylene as the sole feedstock.
- Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
-
supporting information
p. 15708 - 15711
(2013/01/14)
-
- SYNTHESIS OF PARA-XYLENE AND TOLUENE
-
A method of making para-xylene or toluene is carried out by: (a) reacting a C5 or C6 linear monoene (itself, or formed from a C5 or C6 linear alkane) with a hydrogen acceptor in the presence of a hydrogen transfer catalyst to produce a C5 or C6 diene; (b) reacting the C5-C6 diene with ethylene to produce a cyclohexene having 1 or 2 methyl groups substituted thereon; and then (c) either (i) dehydrogenating the cyclohexene in the presence of a hydrogen acceptor with a hydrogen transfer catalyst to produce a compound selected from the group consisting of para-xylene and toluene, or (ii) dehydrogenating the cyclohexene in the absence of a hydrogen acceptor with a dehydrogenation catalyst, to produce para-xylene or toluene.
- -
-
Page/Page column 8-9
(2012/05/20)
-
- Isomerization of 1,5-hexadiene catalyzed by bis-(cyclopentadienyl) lanthanide schiff base/NaH systems; Ln = Sm, Dy, Y, Er
-
Catalytic isomerization of 1,5-hexadiene by Cp2Ln Schiff base/NaH (Schiff base = C14H14NO2, Ln = Sm, Dy, Y, and Er) systems was studied. The isomerization resulted in a mixture of 1,4-hexadiene, 2,4-hexadiene, 1,3-hexadiene, methylene-cyclopentane, and methylcyclopentene. 1,4-Hexadiene and methylenecyclopentane were the intermediate products, while 2,4-hexadiene and methylcyclopentene were the end-products. The effects of the nature of catalyst, temperature, amount of the catalyst, time and solvent, on the isomerization rate and product composition were also studied. The ratio of the linear to the cyclic product in the reaction depended on the amount of catalyst used.
- Yousaf, Muhammad,Qian, Yanlong,Saeed, Muhammad Khalid
-
-
- The stereochemistry of the thermal cheletropic decarbonylation of 3-cyclopentenone as determined by multiphoton infrared photolysis/thermolysis
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There are two allowed pathways for the thermal cheletropic decarbonylation of 3-cyclopentenone. The stereochemistry of decarbonylation of an unconstrained derivative (trans, trans-2,5-dimethyl-3-cyclopentenone, 4) has been determined for the first time. Under conventional pyrolysis conditions, thermal rearrangements of the initial product (trans, trans-2,4-hexadiene, 5) occur at the high temperatures required for the decarbonylation. However, by using multiphoton infrared photolysis/thermolysis to initiate decarbonylation, it was shown that the initial products from thermal decarbonylation of 4 are solely carbon monoxide and stereospecifically 5. The stereochemistry of decarbonylation is thus disrotatory, in accord with prior theoretical studies. A survey of crystal structures reveals ground-state distortions along this reaction coordinate as well.
- Unruh, Gregory R.,Birney, David M.
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p. 8529 - 8533
(2007/10/03)
-
- A new route to diastereonumerically pure cyclopropanes utilizing stabilized phosphorus ylides and γ-hydroxy enones derived from 1,2-dioxines: Mechanistic investigations and scope of reaction
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A new chemical transformation for the construction of diversely functionalized cyclopropanes utilizing 1,2-dioxines and stabilized phosphorus ylides as the key precursors is presented. Through a series of mechanistic studies we have elucidated a clear understanding of the hitherto unknown complex relationship between 1,2-dioxines 1a-e, and their isomeric cis/trans γ-hydroxy enones (23 and 21a-e), cis/trans hemiacetals 24a-e, and β-ketoepoxides (e.g., 26), and how these precursors can be utilized to construct diversely functionalized cyclopropanes. Furthermore, several new synthetically useful routes to these structural isomers are presented. Key features of the cyclopropanation include the ylide acting as a mild base inducing the ring opening of the 1,2-dioxines to their isomeric cis γ-hydroxy enones 23a-e, followed by Michael addition of the ylide to the cis γ-hydroxy enones 23a-e and attachment of the electrophilic phosphorus pole of the ylide to the hydroxyl moiety, affording the intermediate 1-2λ5-oxaphospholanes 4 and setting up the observed cis stereochemistry between H1 and H3. Cyclization of the resultant enolate (30a or 30b), expulsion of triphenylphosphine oxide, and proton transfer from the reaction manifold affords the observed cyclopropanes in excellent diastereomeric excess. The utilization of Co(SALEN)2 in a catalytic manner also allows for a dramatic acceleration of reaction rates when entering the reaction manifold from the 1,2-dioxines. While cyclopropanation is favored by the use of ester-stabilized ylides, the use of keto- or aldo-stabilized ylides results in a preference for 1,4-dicarbonyl formation through a competing Kornblum-De La Mare rearrangement of the intermediate hemiacetals. This finding can be attributed to subtle differences in ylide basicity/nucleophilicity. In addition, the use of doubly substituted ester ylides allows for the incorporation of another stereogenic center within the side chain. Finally, our studies have revealed that the isomeric trans γ-hydroxy enones and the β-keto epoxides are not involved in the cyclopropanation process; however, they do represent an alternative entry point into this reaction manifold.
- Avery, Thomas D.,Taylor, Dennis K.,Tiekink, Edward R.T.
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p. 5531 - 5546
(2007/10/03)
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- 1-Thia-3,4-diazolidine-2,5-dione Functionality: A Photochemical Synthon for the Azo Group
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The 1-thia-3,4-diazolidine-2,5-dione functional group was shown to yield azo compounds upon photolysis.This photoreaction when combined with the known ability of this group to react in a Diels-Alder fashion or as a dinucleophile toward alkylating agents greatly increases the utility of this functionality.The dual reactivity of this group was demonstrated in the synthesis of a number of 3,4-dialkyl-1-thia-3,4-diazolodone-2,5-diones.The photolysis of these compounds produced either thermally stable cyclic azo compounds or the decomposition products of thermally unstable azo compounds.
- Squillacote, Michael,Felippis, James De
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p. 3564 - 3571
(2007/10/02)
-
- Cyclobutene photochemistry. Substituent and wavelenght effects on the photochemical ring opening of monocyclic alkylcyclobutenes
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The photochemical ring opening of cis- and trans-3,4-dimethyl-, 1,3,4-trimethyl-, and 1,2,3,4-tetramethylcyclobutene (1,3, and 4, respectively) has been investigated in hydrocarbon solution with 193 nm and 214 nm light sources.Ring opening is non-stereospecific in all cases at both wavelenghts.The ratio of dienes formed by the formally allowed to formally forbidden pathways in the photolysis of these compounds is highest (ca. 2) for the trimethylcyclobutenes, and approximately 1 for both cis and trans isomers of the di- and tetramethylcyclobutenes with 193 nm excitation.The diene distributions from photolysis of all compounds but cis-3 show slight wavelength dependence.Gas- and solution-phase UV absorption spectra are reported for 3 and 4, and indicate that there are at least three singlet excited states accessible in the 185-230 nm region in these molecules.The ?,R(3s) state is the lowest energy state in the gas phase in 3 and 4.The results verify that orbital symmetry factors do not play a role ( or a consistent one, at least) in controlling the stereochemistry of the reaction, but they do not allow a firm assignment of the excited state(s) responsible for ring opening.Direct photolysis of these compounds also results in fragmentation to yield Z-2-butene (from cis-3 and 4) or E-2-butene (from trans-3 and 4) in addition to propyne or 2-butyne.The 2-butenes are formed with greater than 90percent stereospecifity in all cases.The structures of the four 3-methyl-2,4-hexadiene isomers obtained from photolysis of 3 have been assigned on the basis of 1H NMR spectroscopy and the results of thermolysis of the two cyclobutene isomers.
- Leigh, William J.,Zheng, Kangcheng,Clark, K. Brady
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p. 1988 - 1997
(2007/10/02)
-
- On the Stereochemistry of E'- and E''-Reactions
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The decarboxylative E'-dehydration of β,γ-unsaturated δ-hydroxy acids with DMF-dineopentylacetal shows SYN-faciality irrespective of whether the conformation of the hydroxy group relative to the double bond axis is anticlinal or synclinal.
- Vogel, Ernst,Caravatti, Giorgio,Franck, Peter,Aristoff, Paul,Moody, Christopher,et al.
-
p. 219 - 222
(2007/10/02)
-
- Cyclobutene Photochemistry. Nonstereospecific Photochemical Ring Opening of Simple Cyclobutenes
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The photochemistry of bicyclohept-6-ene, bicyclooct-7-ene, and cis- and trans-3,4-dimetylcyclobutene has been investigated in hydrocarbon solution with monochromatic far-ultraviolet (185 and 193 nm) light sources.All of these simple cyclobutene derivatives undergo ring opening to yield the isomeric 1,3-dienes, and the latter three open nonstereospecifically to yield mixtures of the possible geometric isomers.The isomeric 3,4-dimethylcyclobutenes yield different mixtures of the three 2,4-hexadiene isomers, and in each case the mixtures are weighed in favor of the orbital symmetry forbidden isomer(s).Attempts have been made to analyze the relative isomeric diene yields from ring opening of bicyclooctene and the isomeric 3,4-dimethylcyclobutenes within the context of the purely disrotatory, adiabatic ring-opening mechanism that recent ab initio calculations suggest should be possible.While the results for the former compound are consistant with this mechanism, analysis of the relative yields of the isomeric 2,4-hexadienes from photolysis of the latter two compounds indicates that photochemical ring opening by the formally forbidden, conrotatory pathway may compete to some extent with disrotatory ring opening.
- Clark, K. Brady,Leigh, William J.
-
p. 6086 - 6092
(2007/10/02)
-
- NICKEL CHLORIDE CATALYZED REARRANGEMENT OF ALLYLIC PHOSPHITES
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Allylic phosphites can be rearranged to the corresponding allylic phosphonates under the catalysis of nickel chloride.Dienes and dialkyl phosphonates are formed by an elimination reaction when there is hydrogen atom at the β-position of the carbon-metal bond in the allylic intermediate.The mechanisms of these reactions are discussed.
- Lu, Xiyan,Zhu, Jingyang
-
p. 239 - 244
(2007/10/02)
-
- KINETICS OF 1,5-HEXADIENE HYDROGENATION AND ISOMERIZATION ON A CHROMIUM CATALYST
-
The kinetics of the title reactions was studied in the presence of a catalyst obtained by thermal decomposition of tris(η3-2-propenyl)chromium.The catalyst proved to be active for hydrogenation at 298 K and under 92 kPa H2 but poor for migration of C=C bonds (studied at 333 K).Both the double bonds of the diene may undergo the transformation simultaneously in both the cases studied.Diethyl ether favors deactivation of the hydrogenation catalyst and moderates the isomerization reaction.The kinetic equations for the reactions studied are given.
- Kramarz, Wanda,Kurek, Stefan S.
-
p. 205 - 211
(2007/10/02)
-
- Addition of Dimethylsilanediyl (Dimethylsilylene) to cis,cis-Hexa-2,4-diene: Evidence for a Concerted Vinylsilacyclopropane Rearrangement
-
The formation of cis-3,3-dimethyl-3-silahepta-1,4-diene as the major product from addition of dimethylsilanediyl (dimethylsilylene) to cis,cis-hexa-2,4-diene is believed to result from a concerted 1,5-sigmatropic hydrogen shift in the rearrangement of the vinylsilacyclopropane intermediate formed by concerted 1,2-cis-addition of the silanediyl.
- Lei, Deqing,Gaspar, Peter P.
-
p. 1149 - 1151
(2007/10/02)
-
- Laser-Induced Infrared Multiphoton Isomerization Reactions of 2,4- ans 1,3-Hexadienes
-
Efficient and clean isomerization has been observed in the system consisting of the conjugated 2,4- and 1,3-hexadienes following infrared multiphoton excitaton of these species.Variations of both laser fluence and pressure of the added inert gas are seen to significantly effect branching ratios and yields.Where a competition exists between a low activation energy, low preexponential factor pathway and one with a high activation energy, high preexponential factor, an increase in fluence is seen to favor the latter pathway.An estimate of the degree of excitation in the molecule is obtainable from product branching ratios and inert gas quenching behavior.Photoacoustic measurements of energy input coupled with observation of product ratios indicate that the production of multiple products in a single laser pulse is compatible with a sequential isomerization mechanism which takes place in an almost vibrationally adiabatic fashion.Thermal and CW laser studies of hexadiene isomerization have been performed.Thermal studies yield rate constants and ΔH and ΔS for the various isomers.Thermal studies coupled with multiphoton studies have helped establish the isomerization pathway connecting the cis,trans-2,4- and trans-1,3-hexadiene isomers and have confirmed the other isomerization pathway in the system.The pathways for CW cw laser-induced isomerization have been studied.
- Buechele, James L.,Weitz, Eric,Lewis, Frederick D.
-
p. 868 - 876
(2007/10/02)
-
- Reaction Manifolds of Alkenes with benzene: Stereospecific syn-1,2-Ditosyloxylation of the Carbon-Carbon Double Bond and Other Processes
-
The treatment of various alkenes with benzene (1) in CH2Cl2 gives moderate yields of the corresponding vic-bis(tosyloxy)alkanes (2).When cis- and trans-2-butenes, cis- and trans-2-pentenes, cis-3-hexene, cis-4-octene, and cyclohexene are reactants, the tosyloxy ligands are introduced with syn stereospecifity.With cis- and trans-stilbenes, however, a mixture of meso- and dl-1,2-diphenyl-1,2-bis(tosyloxy)ethanes results from either alkene.Some alkenes react with 1 in a different way.Thus, trans-3-hexene and trans-4-octene with 1 give low yields of 2,5-bis(tosyloxy)-3-hexene and 3,6-bis(tosyloxy)-4-octene, respectively.Evidence is presented that the formation of the bis(tosyloxy)alkenes proceeds via initial oxidation of the trans alkenes by 1 to conjugated dienes and subsequent conjugate ditosyloxylation of the dienes.In a few cases, molecular rearrangements occur.Thus, norbornene with 1 gives 2,7-bis(tosyloxy)norbornane, among other products, while 1,1-diphenylethylene gives deoxybenzoin (major product) and (β,β-diphenylethenyl)phenyliodonium tosylate.The reaction of styrene with 1 depends on the medium; when CH2Cl2 is present, the product is 1-phenyl-1,2-bis(tosyloxy)ethane, but in the absence of solvent, the product is 1,1-bis(tosyloxy)-2-phenylethane.Most alkenes react with 1 to give p-toluenesulfonic acid as a byproduct, and, in rare instances, (iodoxy)benzene is obtained.A mechanism for the vic-ditosyloxylation of alkenes by 1, consistent with the observed syn stereospecificity, is proposed.
- Rebrovic, Louis,Koser, Gerald F.
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p. 2462 - 2472
(2007/10/02)
-
- ADDITION VON VINYL- UND ALLYL-TITAN-BINDUNGEN AN ETHYLEN
-
Reaction of Cp2TiCl (1) with the alkylmagnesium halides 2a-2d, 2g (alkyl = Me, Et, Pr, iso-Pr, hexyl) and ethylene give bis(η5-cyclopentadienyl)(η3-1-methylallyl)titanium (3).Mechanistic investigations indicate that hydrogen transfer from ethylene either to the initially formed Cp2alkytitanium or to Cp2ethyltitanium, formed by βH-elimination to Cp2titaniumhydride and addition to ethylene, leads to liberation of alkane or alkene and ethane and formation of Cp2vinyltitanium F as an intermediate.Insertion to ethylene (even below 0 deg C) into the vinyl-titanium bond of F leads to Cp23-butenyltitanium, which isomerizes to 3.Reaction of 3 at ca. 80 deg C with ethylene in toluene occurs in part with hydrogen transfer to give the butene isomers 4, 5 and F and in part with addition of the allyl-titanium bond to ethylene to give the 2,4-hexadiene isomers 6a-6c by βH-elimination.The compounds 6a-6c are also formed in the catalytic codimerization of butadiene with ethylene in the presence of 3.This reaction has a regioselectivity of above 99percent.
- Lehmkuhl, Herbert,Janssen, Edo,Schwickardi, Renate
-
p. 171 - 180
(2007/10/02)
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- A GENERAL AND STEREOSELECTIVE SYNTHESIS OF (E,E)-CONJUGATED DIENES.
-
Cis-2,5-disubstituted-2,5-dihydrothiophene-1,1-dioxides, generated by a retro Diels-Alder reaction, lead with high stereoselectivity to (E,E)-1,4-disubstituted-1,3-dienes.The efficiency of this method is illustrated by the synthesis of two dienic insect sex pheromones.
- Bloch, R.,Abecassis, J.
-
p. 1247 - 1250
(2007/10/02)
-
- Infrared Photochemistry of Bicyclopropyl
-
The decomposition of bicyclopropyl (C6H10) induced by multiphoton absorption from an infrared laser has been investigated.The reaction produces a complex product mixture consisting mainly of C6H10 isomers.A mechanism is proposed that can rationalize all of the existing infrared photochemical and thermal data on the basis of a single primary step, C-C bond cleavage to a 1,3-biradical.The product mixture results from competitive decay channels of the biradical and successive reactions of the ''hot'' products.This system provides a striking example of the influence of ''hot molecule effects'' on the product distributions in infrared multiphoton dissociation.
- Farneth, William E.,Thomsen, Marcus W.
-
p. 1843 - 1848
(2007/10/02)
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- Titanium Catalyzed Cyclization of 1,5-Hexadienes
-
Cp2TiCl (1) and Cp2TiCl2 (2) combined with isopropylmagnesium bromide (molar ratio 1:1 and 1:2, resp.) catalyze the conversion of 1,5-hexadiene into a mixture of the five-membered ring compounds 3 and 4 as well as the linear isomeric hexadienes 5, 6, and 7.THF is most effective in both promoting cyclization as well as suppressing isomerization (3 -> 4 and 5 -> 6 or 7).The ratio of cyclic to linear products in reactions involving substituted 1,5-hexadienes is found to be dependent upon the position of the substituents.Substitution in the 2- or 2- and 5-position leads to the formation of the open-chain isomers 11 and 12 or 13 and 14, while 3,4-substituted 1,5-hexadienes react to give > 99percent of the five-membered ring systems 15 and 16 or 17 and 18.A reaction mechanism is discussed which involves Cp2TiH and Cp2(alkenyl)Ti intermediates.
- Lehmkuhl, Herbert,Tsien, Yen-Lung
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p. 2437 - 2446
(2007/10/02)
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- -CYCLOADDITION OF SINGLET OXYGEN TO CONJUGATED ACYCLIC HEXADIENES : EVIDENCE OF SINGLET OXYGEN INDUCED cistrans-ISOMERIZATION
-
Addition of singlet oxygen to trans,trans-2,4-hexadiene (1) occurs stereospecifically to give endoperoxide 2.With cis,trans-2,4-hexadiene (4), however, a mixture of diastereomeric endoperoxides, 2 + 5, is observed.Evidence of a singlet oxygen - induced cistrans - isomerization is gained by competitive Diels-Alder reaction of 4 with singlet oxygen/diethyl diazenedicarboxylate.
- Gollnick, Klaus,Griesbeck, Axel
-
p. 3303 - 3306
(2007/10/02)
-
- Thermal Unimolecular Decomposition of Bicyclopropyl and Deuterated Analogues: Infrared Photoactivation as a Diagnostic Tool in Mechanistic Organic Chemistry
-
The infrared photochemistry of bicyclopropyl yields product mixtures that are not easily rationalized on the basis of the mechanistic scheme suggested by previous pyrolysis work.As a result of this inconsistency the thermal chemistry of bicyclopropyl and analogues deuterated specifically on one ring has been reexamined.A significant new reaction channel involving the chemically activated decomposition of cyclohexene to ethylene and butadiene has been demonstrated.Evidence for the involvement of chemically activated cyclohexene is as follows: (1) isotopic labelingstudies implying a symmetric intermediate, (2) a pressure-dependent ratio of cyclohexene to butadiene and ethylene, (3) good agreement between experimental and calculated values for the unimolecular rate constant for retro-Diels-Alder decay of hot cyclohexene.A comprehensive mechanism for the unimolecular decay of bicyclopropyl is proposed.The important elements of this mechanism are a single first-formed 1,3 biradical common to all products and the intervention of chemical activation in the generation of several of the secondary products.
- Farneth, William E.,Thomsen, Marcus W.
-
p. 4851 - 4855
(2007/10/02)
-
- FRAGMENTATION OF PHOSPHORANES: THE REACTION OF Δ3-PHOSPHOLENES WITH PHENANTHRAQUINONE
-
Stereochemically pure cis- and trans-Δ3-phospholenes react with phenanthraquinone to form pentaco-ordinate adducts which, when heated, fragment to trans,-trans-hexa-2,4-diene and phosphonite.The relative rates of fragmentation of the adducts from 1-methyl and 1-aryl phospholenes are reported and discussed.
- Hammond, Philip J.,Lloyd, John R.,Hall, C. Dennis
-
-
- Reaction of Aryl and Vinyl Halides with Zerovalent Nickel-Preparative Aspects and the Synthesis of Alnusone
-
Zerovalent nickel complexes such as bis(1,5-cyclooctadiene)nickel and tetrakis(triphenylphosphine)nickel react rapidly with aryl and vinyl halides to produce the symmetrical coupling products, a low-temperature analogue of the Ullman reaction.The reaction proceeds through oxidative addition of the organic halide to Ni(0), and the reactivity of the Ni(II)intermediates has been examined.Arylnickel halide complexes decompose rapidly to biaryls in DMF.The coupling of simple vinyl halides proceeds with isomerization of the double bond but 3-haloacrylates give efficient co upling with retention of geometry.Cyclizations to form ortho-bridged biaryls are efficient in simple cases (6-, 7-, 8-, 9-, 10-, and 14-membered rings) but fail with an ortho-disubstituted case.The 13-membered meta-bridged cyclic biphenyl, alnusone, is prepared efficiently with the crucial aryl halide coupling to form the ring proceeding in 50percent yield.A side reaction promoted by the presence of protons and with certain ortho-substituted aryl halides is reduction of the aryl halide to the arene.This process can be enhanced by deliberate addition of acid during reaction with Ni(0) and a series of aryl halides underwent succesful reduction.
- Semmelhack, M.F.,Helquist, Paul,Jones, L.D.,Keller, Leonard,Mendelson L.,et al.
-
p. 6460 - 6471
(2007/10/02)
-
- (Alkenyl-η3-allyl)bis(η5-cyclopentadienyl)titanium Complexes
-
Bis(η5-cyclopentadienyl)titanium hydride (Cp2TiH), presumably formed in situ from bis(η5-cyclopentadienyl)titanium dichloride (1) and isopropylmagnesium bromide (2) adds to the conjugated C=C bonds of the alkatrienes 4, 5, 25, 36, and 45 to give the (alkenyl-η3-allyl)bis(η5-cyclopentadienyl)titanium complexes 7 and 10, 8, 26, and 30, 37, 46.The complexes 7, 8, and 26 with the alkenyl group in position 1 isomerize to give the compounds 27, 28, and 29 in which the C=C bond is conjugated with the allyl group.Compound 37 which contains an alkenyl group in a meso-position does not isomerize.In the case of isomycoren (40), TiH addition occurs primarily to the isolated C=C bond followed by intramolecular cyclization to give the bis(η5-cyclopentadienyl)(1-cyclopentyl-η3-allyl)titanium complex 41.
- Lehmkuhl, Herbert,Fustero, Santos
-
p. 1353 - 1360
(2007/10/02)
-
- Organosulfur Compounds, L. - 2H-Thiopyrans and Dihydro-2H-thiopyrans, Synthons for Thiophenes
-
2H-Thiopyran derivatives yield thiophenes on pyrolysis at 240-260 deg C.The influence of substitution in positions 3 to 6 of the 2H-thiopyrans on these new thermal rearrangement and fragmentation reactions is dealt with, and some proposed mechanisms are discussed in detail.A novel three-step synthesis of thiophenes from carbonyl compounds via the corresponding thiones, their -cycloaddition with 1,3-dienes with formation of dihydro-2H-thiopyrans and subsequent thermal conversion is described.In this reaction sequence, whose scope and limitations are outlined, t he thiocarbonyl compound contributes the sulfur and the 1,3-diene the carbon skeleton of the desired thiophenes.
- Praefcke, Klaus,Weichsel, Christian
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p. 1604 - 1619
(2007/10/02)
-