Thiiranation of 2'-adamantylidene-9-benzonorbornenylidene (1) with 4,4'-dithiodimorpholine (5) in Ac2O at -15 degrees C gave thiiranes 2 and 3 without the decomposition of the thermodynamically less stable 3. cis- and trans-Cyclooctenes underwent thiiranation with retention of their stereochemistry.