By@-elimination of 2-chloro-l-(chloromethyl) ethyl methoxymethyl ether (1) under solid- liquid phase-transfer catalytic conditions, 2-(chloromethyl)-3, 5-dioxahex-l-ene (2) of high purity was readily obtained in 85%. Allyl chloride 2 is found to be stable at ambient conditions and to be a superior reagent as CH3COCH2+ synthon for converting active proton-containing compounds such as carboxylic acids, amines, phenols, alcohols, thiols, ...