4-dithiins was developed using sulfur and alkynes. A rhodium complex catalyzes the additionreaction of sulfur with cyclic alkynes giving the corresponding symmetrical 1,4-dithiines under reflux conditions in 2-butanone. Unsymmetrical 1,4-dithiins are synthesized by the reaction of sulfur with dialkyl acetylenedicarboxylates in the presence of cyclic alkynes or vinyl ethers. A convenient synthetic method