Polyisoprenes react with sulfur both intramolecuarly and intermolecularly to yield cyclic sulfides and crosslinked sulfides, respectively. The structures of these have been examined for the reaction of the di-isoprene, 2,6-dimethylocta-2,6-diene, with sulfur at 140°. The cyclic sulfides consist of the two saturated compounds (I) and (II) and the two unsaturated compounds (III) and (IV). The crosslinked sulfide consists of a complex mixture in which unsaturated open chain and saturated and unsaturated cyclic sulfide structures have been identified. The structures of these products suggest a polar reaction mechanism, and also that hydrogen sulfide participates in the reaction. The influence of organic bases, the sulfurizing agent, reaction temperature, and zinc salts on the nature of the sulfur linkage is discussed.