Thiosulfines, also called thiocarbonyl S-sulfides, are compounds with the formula RCSS. Although superficially appearing to be cumulenes, with the linkage RC=S=S, they are more usefully classified as 1,3-dipoles and indeed participate in 1,3-dipolar cycloadditions. Thiosulfines are proposed to exist in equilibrium with dithiiranes, three-membered CS rings. Thiosulfines are often invoked as intermediates in mechanistic discussions of the chemistry of thiones. For example, thiobenzophenone decomposes upon oxidation to the 1,2,4-trithiolane (PhC)S, which arises via the cycloaddition of PhCSS to its parent PhCS.