- A Versatile Synthesis of 1,4-Dienes: Use of Vinyl Ethers as Vinyl Cation Equivalents
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The α,β-dibromo ethers 2, in situ generated from the vinyl ethers 1 and bromine, react with the allylsilanes 3 in the presence of ZnCl2 to give the β-bromo ethers 4.Treatment of 4 with Na in diethyl ether yields 1,4-dienes 5 in 62-79percent overall yield.Key Words: Enol ether / Allylsilane / Bromo ether / 1,4-Diene / Alkoxyalkylation
- Ohm, Stefan,Baeuml, Englbert,Mayr, Herbert
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p. 2785 - 2790
(2007/10/02)
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- Regio- and Stereoselectivity of the Hydrocarbonylating Cyclization of 1,4-Dienes with Carbon Monoxide: Synthesis of (+/-)-(α)-Cuparenone
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Directed towards the synthesis of the cuparene skeleton the hydrocarbonylating cyclization of 1,4-dienes 16, 27 to form cyclopentanones 17, 28 was tested for its regio- and stereoselectivity as well as the toleration of aryl groups in this cyclization met
- Eilbracht, Peter,Balss, Erika,Acker, Michael
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p. 825 - 839
(2007/10/02)
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- Reactions of Methylenecyclopropanes, VII. Nickel(0)-catalysed Cycloadditions of Methylenecyclopropanes with Alkyl Acrylates
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Cycloaddition reactions of methylenecyclopropane (1) and of the ring-methylated methylenecyclopropanes 5, 9, and 12 with alkyl acrylates are performed at nickel(0) catalysts, such as bis(1,5-cyclooctadiene)nickel under mild conditions (0 - 50 deg C).Depending on the degree of methylation of the three-membered ring, 1 and 5 give only alkyl 3-methylenecyclopentanecarboxylates (4 and 6), whereas 9 leads to a mixture of the methylenecyclopentane derivative 10 and the alkyl spirohexanecarboxylate 11, and 12 react to form only the spirohexane derivative 13.With 12 isomerisation to 2,3,3-trimethyl-1,4-pentadiene (15) also takes place.In the case of 9 the ratio of methylenecyclopentane to spirohexanecarboxylate can be influenced by the size of alkyl groups. - In the Ni0-catalysed reactions of 1 with substituted acrylates (methyl crotonate or diethyl maleate) codimerisation to 16 and 17 competes with cyclodimerisation to 2 and 3.
- Binger, Paul,Brinkmann, Axel,Wedemann,Petra
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p. 2920 - 2930
(2007/10/02)
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