Used as a Wittig reagent in organic synthesis, particularly for the conversion of aldehydes into α,β-unsaturated carboxylic acid derivatives. It facilitates the formation of carbon-carbon double bonds with high stereoselectivity, making it valuable in the synthesis of complex molecules such as natural products and pharmaceuticals. Its anhydride functionality allows for further derivatization, enabling the construction of lactones or other cyclic structures through selective ring-opening or condensation reactions. Commonly employed in multi-step synthetic routes where control over double bond geometry and functional group compatibility is essential.