Cyanomethylenetributylphosphorane is primarily used in organic synthesis as a reagent for the Wittig reaction, which is a key method for forming carbon-carbon double bonds. It is particularly effective in the synthesis of alkenes, where it facilitates the conversion of aldehydes and ketones into alkenes with high selectivity and yield. This reagent is valued for its ability to produce less sterically hindered alkenes, making it useful in the preparation of complex organic molecules, including pharmaceuticals and natural products. Additionally, it is employed in the synthesis of fine chemicals and intermediates, contributing to advancements in materials science and chemical research.