We report the oxyalkynylation of thiiranes and thietanes using ethynylbenziodoxolone reagents (EBXs) to readily access functionalized building blocks bearing an alkynyl, a benzoate, and an iodide group. The reaction proceeds with high atom efficiency most likely through an alkynyl-episulfonium intermediate. The transformation is copper-catalyzed and compatible with a large array of thiiranes and thietanes.