Name: titanium-coupled alkenes from carbonyls
Uploaded: 2023-04-30T11:23:04.000Z
Duration: 1 min 22 s
Channel: JoVE

The pinacol coupling reaction involves the radical dimerization of ketones or aldehydes to give vicinal diols.
Among the different metals used as the source of electrons for the reaction, titanium is unusual.
If the reaction is performed at a low temperature, diols can be isolated. Otherwise, titanium reacts further to form alkenes. This forms the basis of the McMurry reaction.
The McMurry reaction proceeds in two steps.
The first step may be analogous to pinacol coupling, where single-electron interactions between the carbonyl oxygens and a reduced titanium species lead to radical&#8211;radical coupling between the carbonyl carbons.
The second step is slow deoxygenation, which leaves the oxygen atoms with the titanium species to yield an alkene.
The intermolecular McMurry reaction typically uses two of the same carbonyl compounds to make tetrasubstituted symmetrical alkenes, often in good yield.
Interestingly, the intramolecular McMurry reaction works well for making large cycloalkenes, like the cyclization of a 15-keto-aldehyde to flexibilene, a natural product with a 15-membered ring.

alkenes via reductive coupling of aldehydes or ketones: mcmurry reaction

Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction

The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
<img alt="Cyclohexanone to bicyclohexyl reaction; TiCl3, LiAlH4; organic synthesis diagram." src="/files/ftp_upload/12907/12907_PT_Figure_1v2.svg" style="text-align: center; height: 80px;" data-altupdatedat="1761830439000" data-alt="Figure1" />
The reaction is a two-step process. The mechanism is still under study, but for some reagent combinations, the first step is similar to the pinacol coupling reaction, involving a single electron transfer from titanium to the carbonyl group to form a ketyl, eventually forming a diol. The second step involves deoxygenation of the diol via binding on the surface of titanium metal particles or coordinating to titanium complexes to yield an alkene. The McMurry coupling reaction involving two same carbonyl compounds gives symmetrical alkenes.
The intramolecular McMurry reaction affords cycloalkenes with eight or more carbon atoms in the ring.

The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used ...

alkenes-via-reductive-coupling-aldehydes-or-ketones-mcmurry

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Organic Chemistry

Unit 1

Radical Chemistry

KEY TERMS AND CONCEPTS

titanium-coupled alkenes from carbonyls

The McMurry reaction turns aldehydes or ketones into alkenes with titanium metal. It first forms a diol-like intermediate through a coupling step, and then removes oxygen to make the double bond. In some cases, this process can be compared to pinacol coupling, which also joins carbonyl compounds.

Titanium acts as a source of electrons in the first step. It transfers a single electron to the carbonyl group and forms a ketyl intermediate. That intermediate can lead to a vicinal diol, which is a molecule with two neighboring alcohol groups.

When titanium stays in the reaction, the diol may react further. The metal or titanium complexes help deoxygenate the diol, and an alkene is produced. If the reaction is stopped at low temperature, the diol can sometimes be isolated instead.

The McMurry coupling of two identical carbonyl compounds gives a symmetrical alkene. An intramolecular McMurry reaction can also close a ring. In that case, it forms cycloalkenes, especially when the ring has eight or more carbon atoms.

Titanium-Coupled Alkenes from Carbonyls

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The McMurry reaction turns aldehydes or ketones into alkenes with titanium metal. It first forms a diol-like intermediate through a coupling step, and then removes oxygen to make the double bond. In some cases, this process can be compared to pinacol coupling, which also joins carbonyl compounds. Titanium acts as a source of electrons in the first step. It transfers a single electron to the carbonyl group and forms a ketyl intermediate. That intermediate can lead to a vicinal diol, which is a...

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key terms and concepts

See how titanium helps convert aldehydes and ketones into alkenes through the McMurry reaction, including diol formation, deoxygenation, and ring closure.

Titanium-Coupled Alkenes from Carbonyls | JoVE K12

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Titanium-Coupled Alkenes from Carbonyls

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