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.[1]
References
^ abcKeck, Gary E.; Boden, Eugene P.; Mabury, Scott A. (March 1985). "A useful Wittig reagent for the stereoselective synthesis of trans-.alpha.,.beta.-unsaturated thiol esters". The Journal of Organic Chemistry. 50 (5): 709–710. doi:10.1021/jo00205a036.