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Peterson olefination
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<h2 id="reaction-mechanism">Reaction mechanism</h2> <p>One attractive feature of the Peterson olefination is that it can be used to prepare either cis- or trans-alkenes from the same β-hydroxysilane. Treatment of the β-hydroxysilane with acid will yield one alkene, while treatment of the same β-hydroxysilane with base will yield the alkene of opposite stereochemistry. </p> <h3>Basic elimination</h3> <p>The action of base upon a β-hydroxysilane (1) results in a concerted <i>syn</i> elimination of (2) or (3) to form the desired alkene. The penta-coordinate <a href="/facts/Silicate/7NdthSRM">silicate</a> intermediate (3) is postulated, but no proof exists to date.[<i>when?</i>] </p> <p><a href="/facts/Potassium/FWPwS7Rj">Potassium</a> alkoxides eliminate quickly, while <a href="/facts/Sodium/eYuSPu2V">sodium</a> alkoxides generally require heating. <a href="/facts/Magnesium/XyIhd2FG">Magnesium</a> alkoxides only eliminate in extreme conditions. The order of reactivity of alkoxides, K > Na >> Mg, is consistent with higher electron density on <a href="/facts/Oxygen/acyn6o8r">oxygen</a>, hence increasing the alkoxide nucleophilicity. </p> <h3>Acidic elimination</h3> <p>The treatment of the β-hydroxysilane (1) with acid results in protonation and an <i>anti</i> elimination to form the desired alkene. </p> <h3>Alkyl substituents</h3> <p>When the α-silyl carbanion contains only <a href="/facts/Alkyl/vmEk8X4v">alkyl</a>, <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a>, or <a href="/facts/Electron_releasing_group/GDzV1DXL">electron-donating substituents</a>, the <a href="/facts/Stereochemical/XkcRVNwd">stereochemical</a> outcome of the Peterson olefination can be controlled,<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a> because at low temperature the elimination is slow and the intermediate β-hydroxysilane can be isolated. </p><p>Once isolated, the diastereomeric β-hydroxysilanes are separated. One <a href="/facts/Diastereomer/ReBkFoCP">diastereomer</a> is treated with acid, while the other is treated with base, thus converted the material to an alkene with the required stereochemistry.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a> </p> <h3>Electron-withdrawing substituents</h3> <p>When the α-silyl carbanion contains electron-withdrawing substituents, the Peterson olefination directly forms the alkene. The intermediate β-hydroxysilane cannot be isolated as it eliminates <i>in-situ</i>. The basic elimination pathway has been postulated in these cases. </p> <h2 id="functional-group-tolerance">Functional group tolerance</h2> <p>Unlike the <a href="/facts/Wittig_reaction/7Cjao2HI">Wittig reaction</a>, Peterson-type olefinations tolerate <a href="/facts/Nitrile/Gz7RCnC6">nitriles</a>.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a> </p> <h2 id="variations">Variations</h2> <p>Acidic elimination conditions are sometimes not feasible as the acid also promotes double bond <a href="/facts/Isomerization/sxv23uKl">isomerization</a>. Additionally, elimination using <a href="/facts/Sodium_hydride/Pnsh2T64">sodium</a> or <a href="/facts/Potassium_hydride/NEp3Vbd7">potassium hydride</a> may not be feasible due to incompatible <a href="/facts/Functional_group/GXkSPsjM">functional groups</a>. Chan <i>et al.</i> have found that acylation of the intermediate silylcarbinol with either <a href="/facts/Acetyl_chloride/SU9Bq4tG">acetyl chloride</a> or <a href="/facts/Thionyl_chloride/nWwvNtvd">thionyl chloride</a> gives a β-silyl <a href="/facts/Ester/FoUAIIw4">ester</a> that will eliminate spontaneously at 25 °C giving the desired alkene.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Corey and co-workers developed a method (sometimes dubbed the <i>Corey-Peterson olefination</i><a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a>) using a silylated imine to yield an α,β-unsaturated aldehyde from a carbonyl compound in one step.<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> For an example for its use in total synthesis see: <a href="/facts/Kuwajima_Taxol_total_synthesis/Pyr7oqdN">Kuwajima Taxol total synthesis</a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Horner%E2%80%93Wadsworth%E2%80%93Emmons_reaction/w3xVWSrw">Horner–Wadsworth–Emmons reaction</a></li> <li><a href="/facts/Tebbe_olefination/367om9CB">Tebbe olefination</a></li> <li><a href="/facts/Wittig_reaction/7Cjao2HI">Wittig reaction</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>D. J. Peterson (1968). "Carbonyl olefination reaction using silyl-substituted organometallic compounds". J. Org. Chem. 33 (2): 780–784. doi:10.1021/jo01266a061. <a href="/wiki/J._Org._Chem." target="_blank">/wiki/J._Org._Chem.</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Birkofer, L.; Stiehl, O. Top. Curr. Chem. 1980, 88, 58. (Review) <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Ager, D. J. Synthesis 1984, 384–398. (Review) <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Ager, D. J. Org. React. 1990, 38, 1. doi:10.1002/0471264180.or038.01 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>T. H. Chan (1977). "Alkene synthesis via β-functionalized organosilicon compounds". Acc. Chem. Res. 10 (12): 442–448. doi:10.1021/ar50120a003. <a href="/wiki/Acc._Chem._Res." target="_blank">/wiki/Acc._Chem._Res.</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>New developments in the Peterson olefination reaction L. Frances van Staden, David Gravestock and David J. Ager Chem. Soc. Rev., 2002,31, 195-200 doi:10.1039/A908402I <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Barrett, A. G. M.; Flygare, J. A.; Hill, J. M.; Wallace, E. M. (1998). "Stereoselective Alkene Synthesis via 1-Chloro-1-[(dimethyl)phenylsilyl]alkanes and α-(Dimethyl)phenylsilyl Ketones: 6-Methyl-6-dodecene". Organic Syntheses; Collected Volumes, vol. 9, p. 580. <a href="http://www.orgsyn.org/demo.aspx?prep=cv9p0580" target="_blank">http://www.orgsyn.org/demo.aspx?prep=cv9p0580</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Ager, D. J. Org. React. 1990, 38, 1. doi:10.1002/0471264180.or038.01 <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Lanari, Daniela; Alonzi, Matteo; Ferlin, Francesco; Santoro, Stefano; Vaccaro, Luigi (3 June 2016). "A Catalytic Peterson-like Synthesis of Alkenyl Nitriles". Organic Letters. 18 (11): 2680–2683. doi:10.1021/acs.orglett.6b01121. ISSN 1523-7060. PMID 27187788. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>T. H. Chan & E. Chang (1974). "Synthesis of alkenes from carbonyl compounds and carbanions alpha to silicon. III. Full report and a synthesis of the sex pheromone of gypsy moth". J. Org. Chem. 39 (22): 3264–3268. doi:10.1021/jo00936a020. PMID 4473100. <a href="/wiki/J._Org._Chem." target="_blank">/wiki/J._Org._Chem.</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>X. Zeng; F. Zeng & E. Negishi (2004). "Efficient and Selective Synthesis of 6,7-Dehydrostipiamide via Zr-Catalyzed Asymmetric Carboalumination and Pd-Catalyzed Cross-Coupling of Organozincs". Org. Lett. 6 (19): 3245–3248. doi:10.1021/ol048905v. PMID 15355023. <a href="/wiki/Org._Lett." target="_blank">/wiki/Org._Lett.</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> <li id="fn:12"><p>E. J. Corey; D. Enders & M. G. Bock (1976). "A simple and highly effective route to α-β-unsaturated aldehydes". Tetrahedron Letters. 17 (1): 7–10. doi:10.1016/S0040-4039(00)71308-6. <a href="/wiki/Tetrahedron_Letters" target="_blank">/wiki/Tetrahedron_Letters</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></p></li> </ol>