Silyl enol ether

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
The general structure of a 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[edit]

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.[4]

Reactions[edit]

C-C Bond formation[edit]

Silyl enol ethers react as nucleophiles in many reactions resulting in alkylation, e.g. Mukaiyama aldol addition and Michael reactions.

Reactions of silylenol ethers.

Halogenation and oxidations[edit]

Halogenation of silyl enol ethers gives haloketones.[5]

Acyloins form upon organic oxidation with an electrophilic source of oxygen such as an oxaziridine or mCPBA.[6]

In the Saegusa–Ito oxidation, certain silyl enol ethers are oxidized to enones with palladium(II) acetate.

Saegusa oxidation

Ring contraction[edit]

Cyclic silyl enol ethers undergo regiocontrolled one-carbon ring contractions.[7][8] 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[edit]

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

References[edit]

  1. ^ Peter Brownbridge (1983). "Silyl Enol Ethers in Synthesis - Part I". Synthesis: 1–28. doi:10.1055/s-1983-30204.
  2. ^ Ian Fleming (2007). A Primer on Organosilicon Chemistry. Wiley. doi:10.1002/9780470513323.ch7.
  3. ^ Nigel D. A. Walshe, Graham B. T. Goodwin, Graham C. Smith, and Frank E. Woodward (1987). "Acetone Trimethylsilyl Enol Ether". Org. Synth. 65: 1. doi:10.15227/orgsyn.065.0001.CS1 maint: Uses authors parameter (link)
  4. ^ Clive, Derrick L. J. & Sunasee, Rajesh (2007). "Formation of Benzo-Fused Carbocycles by Formal Radical Cyclization onto an Aromatic Ring". Org. Lett. 9 (14): 2677–2680. doi:10.1021/ol070849l. PMID 17559217.
  5. ^ Teruo Umemoto, Kyoichi Tomita, Kosuke Kawada (1990). "N-Fluoropyridinium Triflate: An Electrophilic Fluorinating Agent". Organic Syntheses. 69: 129. doi:10.15227/orgsyn.069.0129.CS1 maint: Uses authors parameter (link)
  6. ^ Organic Syntheses, Coll. Vol. 7, p.282 (1990); Vol. 64, p.118 (1986) Article.
  7. ^ (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.
  8. ^ Mitcheltree, M. J.; Konst, Z. A.; Herzon, S. B. Tetrahedron 2013, 69, 5634.