Introduction
<P>Diketene (ketene dimer) is a reactive and versatile reagent in
organic chemistry, which is used for the introduction of functionalized
C
2, C
3, and C
4 units into organic
compounds. Diketene is mostly used for the preparation of acetoacetate
esters and acetoacetamides, which are important synthetic intermediates
used in agrichemical, pharmaceutical, and dyestuffs industries.
[
¹]
Synthesis of five- and
six-membered heterocycles by using diketene has been widely studied.
[
²]
Reactions of the exocyclic
olefin bond, for example photochemical [2+2] reactions,
are other important reactions of diketene.
[
³]
</P><P>In 1908, Wilsmore prepared the first pure sample of the ketene
dimer via thermolysis of acetic anhydride or acetone with a hot
platinum wire.
[
4]
Although diketene
is a small molecule (C
4H
4O
2), in
the absence of modern spectral techniques, it took 40 years to establish
its structure definitely as 4-methylene-2-oxetanone.
[
5]
</P><P>Nowadays, diketene is obtained by ketene dimerization in trickle
towers, into which a liquid stream of the diketene is introduced
in counter current to ketene at 35-40 ˚C (Scheme
[
¹]
).
[
6]
</P>
Scheme 1
<P>In general, depending on the applied reagents and reaction conditions,
ring-opening of diketene results in formation of one of these four
structures which usually undergo further reactions to reach the
desired compounds. (Scheme
[
²]
).
[
7]
</P>
Scheme 2
