Neighbouring group participation by epoxide oxygen in the opening of bromonium ions results in the stereoselective synthesis of cyclic ethers. 9-Oxabicyclo[6.1.0]non-4-ene gives trans,trans-2,6-dibromo-9-oxabicyclo[3.3.1 ]nonane and trans,trans-2,5-dibromo-9-oxabicyclo[4.2.1 ]nonane. Sequential bromination and Bu3SnH reduction converts 1,2-epoxyhex-5-ene into cis- and trans-2,5-dimethyltetrahydrofuran and 2-methyltetrahydropyran while (+)-cis-limonene oxide is converted into non-chiral cineole.