(Ethoxycarbonylmethyl)dimethylsulfonium bromide is a specialty chemical used primarily in organic synthesis as a precursor to sulfonium ylides. It is deprotonated to form the (ethoxycarbonylmethylidene)dimethylsulfonium ylide, which is employed in the Corey-Chaykovsky reaction for the stereoselective synthesis of epoxides from aldehydes and ketones, and cyclopropanes from α,β-unsaturated carbonyl compounds. This reagent is essential for constructing complex organic molecules, including those in pharmaceutical, agrochemical, and materials science applications. Its use extends to asymmetric synthesis for producing chiral building blocks.