McMurrykoppling

McMurrykoppling, often referred to as the McMurry reaction, is a reductive coupling of two carbonyl compounds (aldehydes or ketones) to form an alkene. This organic reaction is typically carried out using a low-valent titanium reagent. The most common reagent system involves the reaction of titanium tetrachloride (TiCl4) with a reducing agent such as zinc, lithium aluminum hydride, or potassium graphite. These reactions are often performed in aprotic solvents like tetrahydrofuran (THF).

The mechanism involves the formation of a titanium-carbene intermediate. This intermediate then undergoes a reductive coupling process. The carbon atoms of the original carbonyl groups are joined together to form a new carbon-carbon double bond, and the oxygen atoms are removed as titanium oxides. The stereochemistry of the resulting alkene, whether it is a cis or trans isomer, can sometimes be influenced by the reaction conditions and the specific substrate.

The McMurry reaction is a powerful tool for synthesizing alkenes, particularly those that may be difficult to prepare by other methods. It is especially useful for intramolecular coupling reactions, leading to the formation of cyclic alkenes. However, the reaction can sometimes suffer from side reactions, such as pinacol coupling (formation of a diol) or the deoxygenation of the carbonyl groups to alkanes. Careful control of reagent stoichiometry and reaction temperature is often necessary for optimal yields.