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In this report, we have established a novel and efficient method for selectively synthesizing either vinyl sulfides or 2-methylbenzothiazoles from the reaction of CaC 2 and disulfides. The selective synthesis of these two distinct products can be controlled by simply adjusting the amount of K 2 S. The underlying reaction mechanism has been thoroughly investigated through control experiments, HRMS, and FTIR, which collectively support the pivotal role of a trisulfur radical anion. This radical species, generated in situ from K 2 S, is essential for the homolytic cleavage of the S-S bonds in a catalytic manner. Additionally, the trisulfur radical anion also acts as an effective mediator for activating the vinyl group of 2-aminophenyl vinyl sulfides, facilitating the crucial intramolecular cyclization required to produce 2-methylbenzothiazoles. Moreover, CaC 2 not only serves as an acetylene source but also creates the basic conditions essential for the selective formation of vinyl sulfides. This methodology demonstrates broad substrate compatibility and excellent functional group tolerance, significantly enhancing its practical utility in diverse synthetic applications.