Used as a Wittig reagent in organic synthesis to convert aldehydes and ketones into α,β-unsaturated esters or related olefins with high stereoselectivity. The (E)-but-2-en-1-yl group is transferred to the carbonyl compound, forming a conjugated diene system after elimination of triphenylphosphine oxide. This transformation is valuable in the synthesis of natural products, pharmaceuticals, and complex molecules where control over double bond geometry is critical. Commonly employed in multi-step syntheses involving terpenes, prostaglandins, and other bioactive compounds requiring (E)-configured alkenes.