Abstract A series of trans-3-chloroallyl ethers and trans-3-thioallyl ethers were stereoselectively synthesized in one step by the reaction of 1-chloro-2,3-epoxypropane or 2,3-epoxypropyl sulfides with alkyl chlorides in the presence of solid sodium hydroxide and quaternary ammonium salt as a phase-transfer catalyst. Phase-transfer catalytic hydroxide ion-initiation followed by stereoselective isomerization of the epoxide ring through β-elimination is postulated as the important part of the reaction pathway.