The reaction of 2-benzylidene-3(2 H)-thianaphthenone-1,1-dioxides (VI) with trialkyl phosphites depends upon the reaction medium. In phenol, compounds having structure VII are produced. In benzene, the 1:1 adducts isolated, wre believed to have a structure similar to X or the corresponding cyclic oxy-phosphorane (XI) which is readily converted into VII by the action of phenol. Dialkyl phosphites react with VI to give the 1:1 adducts (VII) and diphenylphosphinodithioic acid adds to the 2-benzylidenes (VI) in molar ratios to give compounds assigned structure XIV. The IR and NMR spectra of the adducts are recorded.