- Photoinduced electron transfer reaction of 3,3-Dimethyl-3H-pyrazoles: The formation of solvent adducts through cyclopropene derivatives
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3,3-Dimethyl-3H-pyrazoles were photolyzed, and in the presence of 2,4,6-triphenylpyrylium tetrafluoroborate (TPP+) as a sensitizer in acetonitrile; in addition to cyclopropenes, 2H-pyrroles were obtained as solvent adducts to 1,3-radical cation intermediate.
- Miyagawa, Nobukazu,Karatsu, Takashi,Kitamura, Akihide
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- Cyclopropenes as C3 Building Blocks: Cyclopentenols and Large Rings from 2-Aminobicyclopentane Derivatives via Ring-Enlargement Reactions
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The readily available methyl 3,3-dimethylcyclopropene-1-carboxylate undergoes cycloaddition with enamines to give 2-aminobicyclopentane derivatives in moderate to good yields.These compounds are quantitatively transformed into 3-cyclopentenols by treatment with dilute mineral acids.From enamines derived from medium-ring ketones and morpholine, tricyclic adducts are formed, which eliminate morpholine under flash-thermolysis conditions at 600 deg C to give macrocycles containing an E double bond and an allenic system.
- Franck-Neumann, Michel,Miesch, Michel,Kempf, Hubert
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- De l'instabilite des cyclopropenes a double liaison fonctionnalisee monosubstituee. Equilibre non photochimique entre cyclopropenes et vinylcarbenes
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Gem-disubstituted cyclopropenes with a monosubstituted functionalized double bond are in general difficult to isolate, as compared with the corresponding persubstituted compounds.This instability can be accounted for an easy ring opening of these cyclopropenes to vinylcarbenic precursors.Equilibria of this type are demonstrated here by chemical trapping, using i.a. very high pressures, and discussed in terms of steric interactions in the vinylcarbene forms.
- Franck-Neumann, Michel,Miesch, Michel,Barth, Francis,Jenner, Gerard
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p. 661 - 666
(2007/10/02)
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- CYCLOPROPENES ELECTROPHILES: REACTIONS DU MORPHOLINO-1 CYCLOHEXENE AVEC QUELQUES ESTERS GEM-DIMETHYLCYCLOPROPENIQUES; ACCES A DES ANALOGUES HALOPYRETHRIQUES (1).
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Electrophilic cyclopropene esters react with 1-morpholino cyclohexene to give various products depending on the second substituent of the cyclopropene double bond.Enamine alkylation is observed - but not always - as well as different formal cycloaddition reactions.
- Franck-Neumann, M.,Miesch, M.,Kempf, H.
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p. 2933 - 2942
(2007/10/02)
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- The Preparation and Lithiation of 1-Halogenocyclopropenes
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Reaction of a range of 1,1,2-trihalogenocyclopropanes (halogen = bromine, chlorine) with methyl-lithium in ether at -90 - 20 deg C leads to 1,2-dehalogenation to the corresponding 1-halogenocyclopropene.The halogenocyclopropenes are readily lithiated by lithium-halogen exchange with a second equivalent of methyl-lithium to give 1-lithiocyclopropenes, which are in turn trapped by electrophiles; an exception to this is compound (21; X = Cl), which leads to 3-methylbuta-1,2-dienylidene (31) by initial lithium-hydrogen exchange and loss of lithium chloride.The cyclopropenes (5; R = Me, X = Br or Cl) and (21; X = Br or Cl) decompose even at temperatures around ambient, leading either to enynes (6; R = Me) or halogenoalkynes (18; X = Br or Cl).A 12C-labelling study indicates that C-1 of the cyclopropene (21; X = Cl) becomes C-2 of the alkyne (18; X = Cl) on rearrangement.
- Baird, Mark S.,Hussain, Helmi H.,Nethercott, William
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p. 1845 - 1854
(2007/10/02)
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- Oxidative Decarboxylation of Some Bicyclohept-3-ene-1-carboxylic Acids
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Treatment of the bicyclohept-3-ene-1-carboxylic acids (8d-f) with lead tetraacetate results in oxidative decarboxylation and formation of the 1-aryl-1-methylethyl acetates (12a-c).
- Galloway, Neil,Dent, Barry R.,Halton, Brian
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p. 593 - 599
(2007/10/02)
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- Vinylcarbenes acycliques: reactions de cycloadditions intermoleculaires
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The photolysis of 3,3-dimethyl-3H-pyrazoles in unsaturated solvents leads in good yields and often with high stereoselectivity, to vinylcarbene cycloadducts. This direct synthesis of vinylcyclopropanes, vinylcyclopropenes and divinylcyclopropanes shows that acyclic vinyl carbenes are not necessarily intramolecularly stabilized. They can actually be trapped by olefins, acetylenes or dienes, depending on the carbene substituents. Cyano vinyl carbenes are the most efficient intermolecular cycloaddenda examined so far, but carbalkoxy and even ketovinylcarbenes can undergo cyclopropanation reactions with dienes, with little competition from the Wolff rearrangement in the last case.
- Franck-Neumann,Dietrich-Buchecker
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p. 2797 - 2806
(2007/10/09)
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