McMurry reaction

The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to an alkene in the presence of a titanium chloride compound such as titanium(III) chloride and a reducing agent.

The McMurry reaction is named after its discoverer, John E. McMurry, who is currently professor emeritus at Cornell University.

Reaction mechanism


This reductive coupling is related to the Pinacol coupling reaction because in both reactions the first step of the reaction mechanism is one-electron reduction to a ketyl radical ion with a reducing agent such as zinc or zinc / copper and the second step the free radical coupling. The titanium salt is reduced to divalent titanium which forms a titanium(0) adduct with the diol. From this cyclic intermediate the alkene is formed in a concerted rearrangement reaction with generation of titanium oxide.

Scope
The original publication concerned the coupling of retinal to carotene with a titanium(III) trichloride / Lithium aluminium hydride system. In a similar fashion tetraphenylethylene is synthesized from benzophenone. Other dimers formed in the original publication are those of adamantanone and civetone. A McMurry reaction with titanium tetrachloride and zinc is employed in the synthesis of a molecular motor.