Dichotomous Reactivity in the Reaction of Triethyl‐ and Triphenylphosphane HBr Salts with Dimethyl Acetals: A Novel Entry to α‐Alkoxy‐Functionalized Ylides and General Synthesis of Vinyl Ethers and Alkoxy Dienes

Abstract The discovery of dichotomous reactivity in the reaction of trialkyl‐ vs. triphenylphosphane HBr salts with acetals allows entry to functionalized α‐methoxy phosphonium salts and a novel process for tertiary phosphane methylation. The new protocol opens a general entry to the synthesis of vinyl ethers and differentially substituted 1,3‐dienes via Wittig reactions of the functionalized ylides derived from the α‐methoxy phosphonium salts.