Trimethylsulfoxonium iodide is widely used in organic synthesis as a methylating agent and as a precursor to dimethylsulfoxonium methylide. The ylide, generated by deprotonation with a base, is a key reagent in the Corey-Chaykovsky reaction for the stereospecific formation of epoxides from aldehydes and ketones, as well as cyclopropanes from α,β-unsaturated carbonyl compounds. It is effective in transferring methyl groups to nucleophiles such as alcohols, amines, and thiols. Additionally, it finds application in the synthesis of heterocyclic compounds, contributing to the development of pharmaceuticals and agrochemicals. Its stability and reactivity make it a valuable reagent in laboratories focused on synthetic organic chemistry.