1-Thiacyclooct-4-yne (=5,6-Didehydro-3,4,7,8-tetrahydro-2H-thiocin), and Its Sulfoxide and Its Sulfone

1‐Thiacyclooct‐4‐yne (=5,6‐didehydro‐3,4,7,8‐tetrahydro‐2H‐thiocin; 9) can be prepared from thiocan‐5‐one (6) in three steps by applying the so‐called selenadiazole method. The heterocyclic alkyne can be oxidized to the corresponding sulfoxide 16 and sulfone 17. Due to their geometrical strain, all three cyclic alkynes show high reactivities in DielsAlder and 1,3‐dipolar cycloadditions. Moreover, tetrathiafulvalenes can be prepared from 9 and 16 by the reaction with CS2.