Silyl enol ether

Silyl enol ether

Silyl enol ethers in organic chemistry are a class of organic compounds sharing a common functional group composed of an enolate bonded through its oxygen terminus to an organosilicon group.

Silyl enol ethers are important intermediates in organic synthesis.

Organic synthesis

* Trimethylsilyl enol ethers can be prepared from ketones in presence of a strong base and trimethylsilyl chloride.
* Silyl enol ether can form by capturing any enolate formed in a nucleophilic conjugate addition. [Organic Syntheses, Coll. Vol. 9, p.564 (1998); Vol. 73, p.123 (1996) [http://www.orgsynth.org/orgsyn/prep.asp?prep=cv9p0564 Article] ] [Organic Syntheses, Coll. Vol. 8, p.277 (1993); Vol. 66, p. 43 (1988) [http://www.orgsynth.org/orgsyn/prep.asp?prep=cv8p0277 Article] .]
* A rather exotic way to generate silyl enol ethers is via the Brook rearrangement of appropriate substrates. [ R. Tong, F. E. McDonald, Angewandte Chemie, Int. Ed. 2008, 47, 1-4.]

Organic reactions

Silyl enol ethers react as nucleophiles in:
* Mukaiyama aldol addition
* Michael reactions
* Alkylations
* Haloketone formation with halogens [Organic Syntheses, Coll. Vol. 8, p.286 (1993); Vol. 69, p.129 (1990) [http://www.orgsynth.org/orgsyn/prep.asp?prep=cv8p0286 Article] ]
* Acyloin formation by organic oxidation with mCPBA [Organic Syntheses, Coll. Vol. 7, p.282 (1990); Vol. 64, p.118 (1986) [http://www.orgsynth.org/orgsyn/prep.asp?prep=cv7p0282 Article] .]

aegusa oxidation

In the Saegusa oxidation certain silyl enol ethers are oxidized to enones with palladium(II) acetate. In the original publication ["Synthesis of alpha, beta-unsaturated carbonyl compounds by palladium(II)-catalyzed dehydrosilylation of silyl enol ethers" Yoshihiko Ito, Toshikazu Hirao, and Takeo Saegusa J. Org. Chem.; 1978; 43(5) pp 1011 - 1013; DOI|10.1021/jo00399a052] the amount of palladium is less than stochiometric and 1,4-benzoquinone is used as sacrificial catalyst. The intermediate is an oxo-allylpalladium complex.

:

In one application a dienenone is synthesized in two steps from a cyclohexanone ["Formation of Benzo-Fused Carbocycles by Formal Radical Cyclization onto an Aromatic Ring" Derrick L. J. Clive and Rajesh Sunasee Org. Lett.; 2007; 9(14) pp 2677 - 2680; (Letter) DOI|10.1021/ol070849l] [reagents in step 1 are trimethylsilyl triflate and 2,6-lutidine] :

:

Ketene silyl acetals

Ketene silyl acetals are related compounds formally derived from ketenes and acetals with general structure R-C=C(OSiR3)(OR').

References


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