Carbomethoxymethylenetriphenylphosphorane is a chemical compound used in organic syntheses.

Carbomethoxymethylenetriphenylphosphorane can be made via a multistep reaction using bromoacetic acid, dicyclohexylcarbodiimide, and triphenylphosphine.

This makes a phosphonium salt, which is converted to the final product by sodium carbonate in water.

[1] Carbomethoxymethylenetriphenylphosphorane reacts with aldehydes to give a two carbon atom extension.

The carbomethoxymethylene group replaces the oxygen of the aldehyde to give a trans- double bond.