The McMurry reaction is an organic reaction in which two aldehyde or ketone carbonyl groups are coupled to form an alkene using a low-valent titanium catalyst. The key feature of the reaction is that the carbon atoms of the two carbonyl groups become the two carbon atoms of the new carbon–carbon double bond. ^[1,2]

The reaction is named after an American Chemist, John McMurry.

General Reaction

The reaction can be represented as: ^[1]

2 R¹R²C=O –[TiCl₄+Zn–Cl]→ R¹R²C=CR¹R²

The reaction is carried out using low-valent titanium, typically generated by reducing a titanium compound such as TiCl₄ or TiCl₃.

During the reaction:

• a new carbon–carbon bond forms between the two carbonyl carbons;
• the oxygen atoms are removed from the organic product;
• a carbon–carbon double bond is formed.

Depending on the substrate and reaction conditions, alkene products may be obtained as mixtures of E and Z isomers.

Examples

Mechanism

A commonly proposed simplified pathway is as follows. ^[2,4,5]

Step 1: Reduction of the Carbonyl Groups

Low-valent titanium interacts with and reduces the carbonyl groups. This produces titanium-associated, ketyl-like species derived from the original aldehydes or ketones.

Step 2: Carbon–Carbon Bond Formation

The two carbonyl-derived carbon atoms couple with each other. This creates a new carbon–carbon bond and produces a titanium-bound 1,2-diolate (pinacolate-type) intermediate.

Step 3: Deoxygenation and Alkene Formation

The coupled titanium-bound intermediate undergoes further reduction and deoxygenation. The oxygen atoms derived from the original carbonyl groups become associated with titanium-containing species. At the same time, a carbon–carbon double bond forms between the two coupled carbon atoms, producing the final alkene.

McMurry reaction’s ability to join two carbonyl-derived fragments makes it a valuable transformation in organic synthesis, particularly when forming larger or more complex molecular structures.