Enone

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For the character in Greek mythology, see Oenone.
The general structure of an enone
Methyl vinyl ketone, the simplest enone

An enone, also called an α,β-unsaturated carbonyl, is a type of organic compound consisting of an alkene conjugated to a ketone.[1] The simplest enone is methyl vinyl ketone (butenone) or CH2=CHCOCH3. An enal is the corresponding α,β-unsaturated aldehyde, an example being acrolein (CH2=CHCHO).

Synthesis[edit]

Enones are typically producing using an Aldol condensation or Knoevenagel condensation. Some commercially significant enones are produced by condensations of acetone, e.g. mesityl oxide and isophorone.[2]

In the Meyer–Schuster rearrangement the starting compound is a propargyl alcohol. Cyclic enones can be prepared via the Pauson–Khand reaction.

Aldol condensation overview

Reactions[edit]

Enones undergo many kinds of reactions.

They are electrophilic both at the carbonyl carbon but also at the β-carbon. Depending on conditions, either site is attacked by nucleophiles. Addition to the alkene is called conjugate additions. Michael additions are examples.

Enones are often good dienophiles in Diels-Alder reactions. They are activated by Lewis acids, which bind to the carbonyl oxygen.

Enones are readily reduced. They can undergo both reduction of the carbonyl and of the alkene (conjugate reduction), as well as both.

Enones undergo the Nazarov cyclization reaction and in the Rauhut–Currier reaction (dimerization).

Sterically unhindered enones such as methyl vinyl ketone are prone to polymerization.

Enones are good ligands for low-valent metal complexes, examples being Fe(bda)(CO)3 and tris(dibenzylideneacetone)dipalladium(0).

Enones form complexes with low-valent metals.

Related compounds[edit]

Enone is not to be confused with ketene (R2C=C=O). An enamine is a cousin of an enone, with the carbonyl replaced by an amine group.

See also[edit]

References[edit]

  1. ^ Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN 0-471-72091-7 
  2. ^ Hardo Siegel, Manfred Eggersdorfer "Ketones" in Ullmann's Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim.doi:10.1002/14356007.a15_077