- Catalytic reduction and intramolecular cyclization of haloalkynes in the presence of nickel(I) salen electrogenerated at carbon cathodes in dimethylformamide
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Pentylidenecyclopentane can be conveniently prepared in up to 86% yield via the catalytic reduction of 1-iodo- or 1-bromo-5-decyne by [[2,2′-[1,2- ethanediylbis(nitrilomethylidyne)]bis[phenolato]]-N,N′,O,O′] -nickelate(I) electrogenerated at a carbon cathode in dimethylformamide containing tetramethylamnionium tetrafluoroborate. This electrosynthesis can be accomplished at potentials for which the haloalkynes are electroinactive, and it can be completed within 30 min at room temperature. Attempts to synthesize pentylidenecyclobutane and pentylidenecyclohexane from 1-halo-4-nonynes and 11-halo-5-undecynes, respectively, under similar conditions afford the carbocycles in very low yields (2% and 6%, respectively), Other products derived from the various haloalkynes are dimers, alkynes, and 1-alkenynes. Dimers (alkadiynes) arising From 1-halo-4-nonynes and 11-halo-5-undecynes are formed in yields ranging from 80% to 89%, whereas icosa-5, 15-diyne (the dimer obtained from a 1-halo-5-decyne) is found in significantly lower yield (≤ 13%). Alkynes and 1-alkenynes are produced in yields of 3-10% and 2-3%, respectively. A mechanistic scheme, involving alkyn-1-yl radicals arising from niekel(I) salon catalyzed cleavage of the carbon-halogen bond of each haloalkyne, is proposed to account for the formation of all products.
- Ischay, Michael A.,Mubarak, Muhammad S.,Peters, Dennis G.
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p. 623 - 628
(2007/10/03)
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- Transformation of β-chalcogeno alkenylboranes into tetrasubstituted olefins
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In view of generating trisubstituted vinylic chalcogen derivatives, β-chalcogeno alkenylboranes generated through the chalcogen electrophile induced rearrangements of 1-alkynyltrialkyl borates have been subjected to Suzuki-Miyaura coupling and to boron to copper transmetalation followed by alkylation. Some of the trisubstituted vinyl sulfides obtained by this latter strategy have been converted efficiently into the title olefins through the NiCl2(dmpe) catalyzed coupling with various Grignard reagents.
- Gerard, Julien,Hevesi, László
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p. 367 - 381
(2007/10/03)
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- Cyclizations during the Grignard Reactions of ω-Bromoalkynes
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The Grignard reactions of a number of ω-bromoalkynes have been shown to undergo regioselective cyclizations in certain instances to give the smaller possible carbocycle. These cyclizations are shown to result from two competing processes, whose relative efficiencies depend upon the chain length and the remote substitutent on the acetylene. These are interpreted as a radical cyclization which occurs only during the time the Grignard is being formed from the bromide and an organometallic reaction which slowly transforms the Grignard reagent into its cyclic isomer. The mechanistic details of these transformations are discussed.
- Crandall, Jack K.,Michaely, William J.,Collonges, Francois,Nelson, Deanna J.,Ayers, Timothy A.,Gajewski, Joseph J.
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p. 1473 - 1490
(2007/10/03)
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- INTRAMOLECULAR ADDITION OF ALKYLLITHIUMS TO ACETYLENES: REGIOSPECIFIC 4-, 5-, and 6-EXO-DIG CYCLIZATIONS
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Primary acetylenic alkyllithiums bearing a phenyl substituent on the triple bond, which may be prepared in virtually quantitative yield by low-temperature lithium-iodine interchange, undergo regiospecific exo-dig cyclization via stereoselective syn-additi
- Bailey, William F.,Ovaska, Timo V.
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p. 627 - 630
(2007/10/02)
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- REDUCTION DE DERIVES D'ALCOOLS PROPARGYLIQUES CATALYSEE PAR UN COMPLEXE DE PALLADIUM ZEROVALENT
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Catalysis by tetrakis(triphenylphosphine)palladium of the reaction of hydride donnors with secondary propargylic bromides, mesylates and phosphates increases markedly the amount of allene produced.The best results in that direction are obtained with mesylates and phosphates by using lithium triethylborohydride.The reaction then occurs with an ANTI introduction of the hydride with respect to the leaving group.A mechanism is proposed which explains the influence of the various parameters of the reaction.
- Colas, Yann,Cazes, Bernard,Gore, Jacques
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p. 165 - 173
(2007/10/02)
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- REGIO ET STEREOCHIMIE DE LA REDUCTION DE DERIVES D'ALCOOLS PROPARGYLIQUES CATALYSEE PAR UN COMPLEXE DE PALLADIUM (O)
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Regio and stereoselectivity of the palladium catalyzed reduction of propargylic halides and esters is greatly influenced by the nature of the hydride donor as by the leaving group.Best results in allene formation are observed in the reduction by lithium triethylborohydride of mesylates and phosphates.In the former case, reaction occurs with anti displacement of the sulfonyl group.
- Colas, Yann,Cazes, Bernard,Gore, Jacques
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p. 845 - 848
(2007/10/02)
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- Cyclizations of ω-Alkynyl Halides by Cr(II) Reduction
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Reduction of halides of the types RCC(CH2)nX with Cr(II) in aqueous DMF containing ethylenediamine proceeds by way of the intermediate radicals which cyclize regioselectively in the n=4 and n=5 cases to give substituted methylenecycloalkanes.Experimental conditions which favor longer lifetimes for the intermediate radicals (low concentrations, slow addition times, and an inverse-addition mode) result in increased cyclization.The iodides curiously give more cyclic product than the corresponding bromides.These results are discussed.
- Crandall, Jack. K.,Michaely, W. J.
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p. 4244 - 4248
(2007/10/02)
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