Wittig Reaction - Examples of Use

Examples of Use

Because of its reliability and wide applicability, the Wittig reaction has become a standard tool for synthetic organic chemists.

The most popular use of the Wittig reaction is for the introduction of a methylene group using methylenetriphenylphosphorane (Ph₃P=CH₂). In the example shown, even a sterically hindered ketone such as camphor can be successfully converted to its methylene derivative by heating with methyltriphenylphosphonium bromide and potassium tert-butoxide, which generate the Wittig reagent in situ. In another example, the phosphorane is produced using sodium amide as a base, and this successfully converts the aldehyde shown into alkene I in 62% yield. The reaction is performed in cold THF, and the sensitive nitro, azo and phenoxide groups all survive intact. The product can be used to incorporate a photostabiliser into a polymer, to protect the polymer from damage by UV radiation.

Another example of its use is in the synthesis of leukotriene A methyl ester. The first step uses a stabilised ylide, where the carbonyl group is conjugated with the ylide preventing self condensation, although unexpectedly this gives mainly the cis product. The second Wittig reaction uses a non-stabilised Wittig reagent, and as expected this gives mainly the cis product. Note that the epoxide and ester functional groups survive intact.

Methoxymethylenetriphenylphosphine is a Wittig reagent for the homologation of aldehydes.