A novel method for metal‐free oxothiolation of ynamides to construct oxazolidine‐2,4‐diones bearing sulfur‐substituted quaternary carbonatoms has been developed. It represents a rare C−O bond cleavage of ynamides, as well as a facile and tandem approach for the formation of C−O, C−S, and C−Cl bonds. This redox‐neutral protocol can be applied to the synthesis of multisubstituted oxazolidine‐2,4‐diones