- One-pot Synthesis of 1,3-Butadiene and 1,6-Hexanediol Derivatives from Cyclopentadiene (CPD) via Tandem Olefin Metathesis Reactions
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A novel tandem reaction of cyclopentadiene leading to high value linear chemicals via ruthenium catalyzed ring opening cross metathesis (ROCM), followed by cross metathesis (CM) is reported. The ROCM of cyclopentadiene (CPD) with ethylene using commercially available 2nd gen. Grubbs metathesis catalysts (1-G2) gives 1,3-butadiene (BD) and 1,4-pentadiene (2) (and 1,4-cyclohexadiene (3)) with reasonable yields (up to 24 % (BD) and 67 % (2+3) at 73 % CPD conversion) at 1–5 mol % catalyst loading in toluene solution (5 V% CPD, 10 bar, RT) in an equilibrium reaction. The ROCM of CPD with cis-butene diol diacetate (4) using 1.00 - 0.05 mol % of 3rd gen. Grubbs (1-G3) or 2nd gen. Hoveyda-Grubbs (1-HG2) catalysts loading gives hexa-2,4-diene-1,6-diyl diacetate (5), which is a precursor of 1,6-hexanediol (an intermediate in polyurethane, polyester and polyol synthesis) and hepta-2,5-diene-1,7-diyl diacetate (6) in good yield (up to 68 % or TON: 1180). Thus, convenient and selective synthetic procedures are revealed by ROCM of CPD with ethylene and 4 leading to BD and 1,6-hexanediol precursor, respectively, as key components of commercial intermediates of high-performance materials.
- Turczel, Gábor,Kovács, Ervin,Csizmadia, Eszter,Nagy, Tibor,Tóth, Imre,Tuba, Robert
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p. 4884 - 4891
(2018/09/25)
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- Une synthese hautement stereoselective de dienes conjugues (E)
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A general method for the preparation of (E) terminal conjugated dienes was developed by the flash thermolysis of 2-substituted 2,5-dihydrothiophene-1,1-dioxides generated by a retro Diels-Alder reaction.This process allows the obtention of conjugated dienes, bearing or not a functionality (alcohols, esters), with an excellent stereoisomeric purity (in general higher than 98percent).An application to the synthesis of (E)-9,11-dodecadien-1-yl acetate, the major component of the sex pheromone of Diparopsis castanea, shows the generality and the efficacy of this method.
- Bloch, R.,Abecassis, J.,Hassan, D.
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p. 2019 - 2024
(2007/10/02)
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- Electron Delocalisation and Stabilisation in Heptatrienyl and Polyenyl Radicals
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Heptatrienyl radicals were generated by hydrogen abstraction from hepta-1,3,6-triene with t-butoxyl radicals and observed by e.s.r. spectroscopy.The hyperfine splittings of heptatrienyl and other polyenyl radicals indicate that spin density is not uniformly distributed along the chain but more concentrated around the central region of the structure.Semi-empirical SCF MO calculations agree with this result and also show that most radical character is associated with the central region.The stabilisation energies (SE) of polyenyl radicals increase with chain lenght and are related to the hydrogen hyperfine splittings (G) of SEESR/kJ mol-1 = 375 +/- 4 - (272+/-)log101)/G> (i) the terminal methylene groups
- Green, Iain G.,Walton, John C.
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p. 1253 - 1258
(2007/10/02)
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- Organic Photochemistry with 6.7-eV Photons: The Photochemistry of Bicyclohept-2-ene (2-Norcarene)
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The photochemistry of bicyclohept-2-ene (2-norcarene) upon direct and triplet-sensitized photolysis has been investigated.The results differ significantly from those of previous studies on related systems.Direct photolysis with monochromatic radiation in the region 185-230 nm leads to a variety of products, of which cis-1,3,6-heptadiene, the major product, is shown by deuterium labeling studies to result from formal electrocyclic ring opening in a manner analogous to the 1,3-cyclohexadiene/1,3,5-hexatriene interconversion.The evidence suggests that this process may occur via a concerted mechanism in the singlet state.The other products arise from activation of the two cyclopropane bonds that are in conjugation with the olefinic group.The product distribution is independent of both solvent and excitation wavelength and is unchanged by the addition of naphthalene.Toluene-sensitized photolysis results in the formation of cis-1,3,6-heptatriene and bicyclohept-2-ene, which can be rationalized as resulting from decay of a common biradical intermediate.
- Leigh, William J.,Srinivasan, R.
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p. 514 - 519
(2007/10/02)
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- Methyltriphenoxyphosphonium Iodide (MTPI); Induced Dehydration and Dehydrohalogenation in Aprotic Solvents
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Methyltriphenoxyphosphonium iodide (MTPI) is an effective dehydration and dehydrohalogenation reagent under mild conditions when 1,3-dimethylimidazolidin-2-one is used as an aprotic solvent in place of the more normally used hexamethylphosphoric triamide (HMPT).Since previosly suggested mechanisms had proposed alcohol-HMPT interaction as an important mechanistic step, this result coupled with comparative product geometric isomer distributions and the conjugated: non-conjugated triene product ratios leads to the conclusion that MTPI-alcohol interaction with displacement of phenoxide is the primary step in the reaction.In dimethyl sulphoxide (DMSO) alcohol dehydratation is hindered by DMSO-MTPI interaction yielding dimethyl sulphide.
- Spangler, Charles W.,Kjell, Douglas P.,Wellander, Lori L.,Kinsella, Mary A.
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p. 2287 - 2289
(2007/10/02)
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