Sulfonium ylides are a class of chemical compounds characterized by a positively charged sulfur atom bonded to a negatively charged carbon atom. They are typically formed by the reaction of a sulfonium salt with a strong base, resulting in a species that can act as a nucleophile in various chemical reactions. These ylides are important in organic synthesis, particularly in the Wittig reaction, where they are used to create alkenes from carbonyl compounds. Their unique structure allows them to participate in a range of reactions, making them valuable intermediates in the development of complex organic molecules.