The Peterson olefination (also called the Peterson reaction) is the
chemical reactionof α-silyl carbanions 1 with ketones (or aldehydes) to form a β-hydroxysilane 2 which eliminates to form alkenes 3.cite journal | author = D. J. Peterson | title = Carbonyl olefination reaction using silyl-substituted organometallic compounds | year = 1968 | journal = J. Org. Chem.| volume = 33 | issue = 2 | pages = 780–784 | doi = 10.1021/jo01266a061]
Several reviews have been published.Birkofer, L.; Stiehl, O. "Top. Curr. Chem." 1980, "88", 58. (Review)] Ager, D. J. "Synthesis" 1984, 384-398. (Review)] Ager, D. J. "Org. React." 1990, "38", 1-223. (Review)] cite journal | author = T. H. Chan | title = Alkene synthesis via β-functionalized organosilicon compounds | year = 1977 | journal =
Acc. Chem. Res.| volume = 10 | issue = 12 | pages = 442–448 | doi = 10.1021/ar50120a003]
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.
The action of base upon a β-hydroxysilane 1 results in a concerted "syn" elimination of 2 or 3 to form the desired alkene. The penta-coordinate
siliconintermediate 3 is postulated, but no proof exists to date. Potassiumalkoxides eliminate quickly, while sodiumalkoxides generally require heating. Magnesiumalkoxides only eliminate in extreme conditions. The order of reactivity of alkoxides, K > Na >> Mg, is consistent with higher electron density on oxygen, hence increasing the alkoxide nucleophilicity.
The treatment of the β-hydroxysilane 1 with acid results in protonation and an "anti" elimination to form the desired alkene.
When the α-silyl carbanion contains only
alkyl, hydrogen, or electron-donating substituents, the stereochemicaloutcome of the Peterson olefination can be controlled,OrgSynth | author = Barrett, A. G. M.; Flygare, J. A.; Hill, J. M.; Wallace, E. M. | collvol = 9 | collvolpages = 580 | year = 1998 | prep = cv9p0580 | title = Stereoselective Alkene Synthesis via 1-Chloro-1- [(dimethyl)phenylsilyl] alkanes and α-(Dimethyl)phenylsilyl Ketones: 6-Methyl-6-dodecene] because at low temperature the elimination is slow and the intermediate β-hydroxysilane can be isolated.
Once isolated, the diastereomeric β-hydroxysilanes are separated. One
diastereomeris treated with acid, while the other is treated with base, thus converted the material to an alkene with the required stereochemistry.
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 "in-situ". The basic elimination pathway has been postulated in these cases.
Acidic elimination conditions are sometimes not feasible as the acid also promotes double bond
isomerization. Additionally, elimation using sodium or potassium hydridemay not be feasible due to incompatible functional groups. Chan "et al." have found that acylation of the intermediate silylcarbinol with either acetyl chlorideor thionyl chloridegives a β-silyl esterthat will eliminate spontaneously at 25°C giving the desired alkene.cite journal | author = T. H. Chan and E. Chang | title = Synthesis of alkenes from carbonyl compounds and carbanions alpha to silicon. III. Full report and a synthesis of the sex pheromone of gypsy moth | year = 1974 | journal = J. Org. Chem.| volume = 39 | issue = 22 | pages = 3264–3268 | doi = 10.1021/jo00936a020] Corey and co-workers developed a method (sometimes dubbed the "Corey-Peterson olefination"cite journal | author = X. Zeng, F. Zeng and E. Negishi | title = Efficient and Selective Synthesis of 6,7-Dehydrostipiamide via Zr-Catalyzed Asymmetric Carboalumination and Pd-Catalyzed Cross-Coupling of Organozincs | year = 2004 | journal = Org. Lett.| volume = 6 | issue = 19 | pages = 3245–3248 | doi = 10.1021/ol048905v] ) using a silylated imine to yield an α,β-unsaturated aldehyde from a carbonyl compound in one step. cite journal | author = E. J. Corey, D. Enders and M. G. Bock | title = A simple and highly effective route to α-β-unsaturated aldehydes | year = 1976 | journal = Tetrahedron Letters| volume = 17 | issue = 1 | pages = 7–10 | doi = 10.1016/S0040-4039(00)71308-6]
For an example for its use in total synthesis see:
Kuwajima Taxol total synthesis
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