Alqueno: Diferenzas entre revisións
Contido eliminado Contido engadido
Liña 252:
=== Síntese a partir de alquenos: metátese de olefinas e hidrovinilación ===
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Os alquenos poden pepararse por intercambio con outros alquenos nunha reacción chamada [[metátese de olefinas]]. Frecuentemente, a perda de gas eteno utilízase para impulsar a reacción cara a un produto desexado. En moitos casos, obtense unha mestura de isómeros xeométricos, pero a reacción tolera moitos grupos funcionais. O método é particularmente efectivo para a preparación de alquenos cíclicos, como na síntese de [[muscona]]:
Transition metal catalyzed hydrovinylation is another important alkene synthesis process starting from alkene itself.<ref name=Vogt2010>{{cite journal | author = Vogt, D. | year = 2010 | pages = 7166–8 | title = Cobalt-Catalyzed Asymmetric Hydrovinylation | issue = 40 | pmid = 20672269 | journal = Angew. Chem. Int. Ed. | volume = 49 | doi = 10.1002/anie.201003133 }}</ref> In general, it involves the addition of a hydrogen and a vinyl group (or an alkenyl group) across a double bond. The hydrovinylation reaction was first reported by Alderson, Jenner, and Lindsey by using rhodium and ruthenium salts, other metal catalysts commonly employed nowadays included iron, cobalt, nickel, and palladium. The addition can be done highly regio- and stereoselectively, the choices of metal centers, ligands, substrates and counterions often play very important role.<ref name=Vogt2006 >{{cite journal | author = Grutters, M. M. P. |author2=Muller, C. |author3=Vogt, D. | year = 2006 | pages = 7414–5 | title = Highly Selective Cobalt-Catalyzed Hydrovinylation of Styrene | issue = 23 | pmid = 16756275| journal = J. Am. Chem. Soc. | volume = 128 | doi = 10.1021/ja058095y }}</ref><ref name=Hilt2009 >{{cite journal | author = Hilt, G. |author2=Danz, M. |author3=Treutwein, J. | year = 2009 | pages = 3322–5 | title = Cobalt-Catalyzed 1,4-Hydrovinylation of Styrenes and 1-Aryl-1,3-butadienes | issue = 15 | pmid = 19583205 | journal = Org. Lett. | volume = 11 | doi = 10.1021/ol901064p }}</ref><ref name=RajanBabu2010 >{{cite journal | author = Sharma, R. K. |author2=RajanBabu, T. V. | year = 2010 | pages = 3295–7 | title = Asymmetric Hydrovinylation of Unactivated Linear 1,3-Dienes | issue = 10 | pmid = 20163120| journal = J. Am. Chem. Soc. | pmc = 2836389 | volume = 132 | doi = 10.1021/ja1004703 }}</ref> Recent studies showed that the use of N-heterocyclic carbene with Ni can be useful for the selective preparations of functionalized geminal olefins or 1,1-disubstituted alkenes.<ref name=Ho2010>{{cite journal | author = Ho, C.-Y. |author2=He, L. | year = 2010 | pages = 9182–9186 | title = Catalytic Intermolecular Tail-to-Tail Hydroalkenylation of Styrenes with alpha-Olefins: Regioselective Migratory Insertion Controlled by a Nickel/N-Heterocyclic Carbene | issue = 48 | pmid = 20853303 | journal = Angew. Chem. Int. Ed. | volume = 49 | doi = 10.1002/anie.201001849 }}</ref><ref name=Ho2012>{{cite journal | author = Ho, C.-Y. |author2=He, L. | year = 2012 | pages = 1481–1483 | title = Shuffle Off the Classic Beta-Si Elimination by Ni-NHC Cooperation: Implication for C–C Forming Reactions Involving Ni-Alkyl-Beta-Silanes | issue = 10 | pmid = 22116100 | journal = Chem. Commun. | volume = 48 | doi = 10.1039/c1cc14593b }}</ref>▼
[[Ficheiro:MusconeViaRCM.png|500px|center|A metátese de cerre de aneis utilizada na síntese de muscona]]
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=== Síntese a partir de alquinos ===
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Reduction of [[alkyne]]s is a useful method for the [[stereoselectivity|stereoselective]] synthesis of disubstituted alkenes. If the ''cis''-alkene is desired, [[hydrogenation]] in the presence of [[Lindlar's catalyst]] (a heterogeneous catalyst that consists of palladium deposited on calcium carbonate and treated with various forms of lead) is commonly used, though hydroboration followed by hydrolysis provides an alternative approach. Reduction of the alkyne by [[sodium]] metal in liquid [[ammonia]] gives the ''trans''-alkene.<ref name="ZweifelNantz">{{cite book | last = Zweifel | first = George S. |author2=Nantz, Michael H.| title = Modern Organic Synthesis: An Introduction | publisher = W. H. Freeman & Co. | location = New York | year = 2007 | pages = 366 | isbn = 0-7167-7266-3 }}</ref>
Liña 266:
For the preparation multisubstituted alkenes, [[carbometalation]] of alkynes can give rise to a large variety of alkene derivatives.
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=== Rearranxos e reaccións relacionadas ===
Os alquenos poden sintetizarse a partir doutros alquenos por [[reacción de rearranxo|reaccións de rearranxo]] ou redistribución. Ademais da [[met´ñatese de olefinas]] (descrita [[#Metátese de olefinas|arriba]]), poden utilizarse moitas [[reacción pericíclica|reaccións pericíclicas]] como a [[reacción eno]] e o [[rearranxo de Cope]].
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