5194-50-3Relevant academic research and scientific papers
ADDITION VON VINYL- UND ALLYL-TITAN-BINDUNGEN AN ETHYLEN
Lehmkuhl, Herbert,Janssen, Edo,Schwickardi, Renate
, p. 171 - 180 (1983)
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.
Addition of Dimethylsilanediyl (Dimethylsilylene) to cis,cis-Hexa-2,4-diene: Evidence for a Concerted Vinylsilacyclopropane Rearrangement
Lei, Deqing,Gaspar, Peter P.
, p. 1149 - 1151 (1985)
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.
Applications of PC(sp3)P iridium complexes in transfer dehydrogenation of alkanes
Bzier, David,Brookhart, Maurice
, p. 3411 - 3420 (2015/02/19)
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.
Synthesis of p-xylene from ethylene
Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
supporting information, p. 15708 - 15711,4 (2012/12/11)
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.
Synthesis of p-xylene from ethylene
Lyons, Thomas W.,Guironnet, Damien,Findlater, Michael,Brookhart, Maurice
supporting information, p. 15708 - 15711 (2013/01/14)
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.
SYNTHESIS OF PARA-XYLENE AND TOLUENE
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Page/Page column 8-9, (2012/05/20)
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.
Perturbations by phenyl on the 1,5-hydrogen shift in 1,3(Z)-pentadiene. Another chameleonic transition region?
Doering, William Von E.,Keliher, Edmund J.,Zhao, Xin
, p. 14206 - 14216 (2007/10/03)
The acyclic 1,5-dienyl hydrogen shift is accelerated by radical-stabilizing phenyl substituents without regard to the type of position occupied in the 1,3(Z)-pentadiene system. 1-Phenyl-5-p-tolyl-1,3(Z)-pentadiene has a corrected energy of activation 5.8 kcal mol-1 lower than that of the parent, while the 2-and 3-phenyl analogues, examined in cyclic systems specifically designed to obviate the otherwise general need for a thermochemical correction to the immediately precursory s-cis conformation, reveal stabilizing effects of 3.6 and 3.4 kcal mol-1, respectively. These relatively small effects are consistent with a chameleonic conceptual scheme for the transition region.
The stereochemistry of the thermal cheletropic decarbonylation of 3-cyclopentenone as determined by multiphoton infrared photolysis/thermolysis
Unruh, Gregory R.,Birney, David M.
, p. 8529 - 8533 (2007/10/03)
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.
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
Avery, Thomas D.,Taylor, Dennis K.,Tiekink, Edward R.T.
, p. 5531 - 5546 (2007/10/03)
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.
1-Thia-3,4-diazolidine-2,5-dione Functionality: A Photochemical Synthon for the Azo Group
Squillacote, Michael,Felippis, James De
, p. 3564 - 3571 (2007/10/02)
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.
