Silyl enol ether
Silyl enol ethers in organic chemistry are a class of organic compounds that share a common functional group composed of an enolate bonded through its oxygen end to an organosilicon group. They are important intermediates in organic synthesis.[1][2]
Synthesis
Trimethylsilyl enol ethers can be prepared from ketones in presence of a strong base and trimethylsilyl chloride or a weak base and trimethylsilyl triflate. [3] Alternatively, enolate salts react with silyl electrophiles.
A rather exotic way to generate silyl enol ethers is via the Brook rearrangement of appropriate substrates.
Reactions
C-C Bond formation
Silyl enol ethers react as nucleophiles in many reactions resulting in alkylation, e.g. Mukaiyama aldol addition and Michael reactions.
Halogenation and oxidations
Halogenation give haloketones.[4]
Acyloins form upon organic oxidation with an electrophilic source of oxygen such as an oxaziridine or mCPBA.[5]
In the Saegusa–Ito oxidation, certain silyl enol ethers are oxidized to enones with palladium(II) acetate.
Ring contraction
Cyclic silyl enol ethers undergo regiocontrolled one-carbon ring contractions.[6][7] These reactions employ electron-deficient sulfonyl azides, which undergo chemoselective, uncatalyzed [3+2] cycloaddition to the silyl enol ether, followed by loss of dinitrogen, and alkyl migration to give ring-contracted products in good yield. These reactions may be directed by substrate stereochemistry, giving rise to stereoselective ring-contracted product formation.
Ketene silyl acetals
Ketene silyl acetals are related compounds formally derived from ketenes and acetals with general structure R-C=C(OSiR3)(OR').
References
- ^ Peter Brownbridge (1983). "Silyl Enol Ethers in Synthesis - Part I". Synthesis: 1–28. doi:10.1055/s-1983-30204.
- ^ Ian Fleming (2007). A Primer on Organosilicon Chemistry. Wiley. doi:10.1002/9780470513323.ch7.
- ^ "Acetone Trimethylsilyl Enol Ether". Org. Synth. 65: 1. 1987. doi:10.15227/orgsyn.065.0001.
{{cite journal}}: Unknown parameter|authors=ignored (help) - ^ Organic Syntheses, Coll. Vol. 8, p.286 (1993); Vol. 69, p.129 (1990) Article
- ^ Organic Syntheses, Coll. Vol. 7, p.282 (1990); Vol. 64, p.118 (1986) Article.
- ^ (a) Wohl, R. Helv. Chim. Acta 1973, 56, 1826. (b) Xu, Y. Xu, G.; Zhu, G.; Jia, Y.; Huang, Q. J. Fluorine Chem. 1999, 96, 79.
- ^ Mitcheltree, M. J.; Konst, Z. A.; Herzon, S. B. Tetrahedron 2013, 69, 5634.