The enthalpies of formation Δ H f and the ring strain energies E g were calculated for the nine isomeric dithiacyclooctynes 1‐‐9 by applying the MNDO method. Reaction Scheme 2 shows the synthesis of 1,4‐dithia‐2‐cyclooctyne (1), which was the highest E g value in this series. It dimerizes to 13 in the absence of reaction partners. Scheme 4 summarizes the preparation of 1,5‐dithia‐2‐cyclooctyne (2) and its homologue 1,5‐dithia‐2‐cyclononyne (23) and Scheme 6 the preparation of 1,4‐dithia‐6‐cyclooctyne (6) and its homologue 1,5‐dithia‐7‐cyclononyne (29). Depending on the position of the sulfur atoms, all three reaction sequences contain different steps for the introduction of the triple bonds.

Dithiacyclooctine