Silyl enol ether

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

Silyl enol ethers are important intermediates in organic synthesis.

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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.^[1][2]

Organic reactions

Silyl enol ethers react as nucleophiles in:

• Mukaiyama aldol addition
• Michael reactions
• Alkylations
• Haloketone formation with halogens^[3]
• Acyloin formation by organic oxidation with mCPBA^[4]

Saegusa oxidation

In the Saegusa oxidation certain silyl enol ethers are oxidized to enones with palladium(II) acetate. In the original publication ^[5] 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 ^{[6] [7]}:

Ketene silyl acetals

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

References

1. ^ Organic Syntheses, Coll. Vol. 9, p.564 (1998); Vol. 73, p.123 (1996) Article
2. ^ Organic Syntheses, Coll. Vol. 8, p.277 (1993); Vol. 66, p. 43 (1988) Article.
3. ^ Organic Syntheses, Coll. Vol. 8, p.286 (1993); Vol. 69, p.129 (1990) Article
4. ^ Organic Syntheses, Coll. Vol. 7, p.282 (1990); Vol. 64, p.118 (1986) Article.
5. ^ 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
6. ^ 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
7. ^ reagents in step 1 are trimethylsilyl triflate and 2,6-lutidine