4-Phenylsulfanyl-2-(2-phenylsulfanylethyl) but-1-ene () has proved to be an appropriate and new 3-methylidenepentane-1, 5-dianion synthon. The reaction of with an excess of lithium powder and a catalytic amount of DTBB (2.5%) in the presence of a carbonyl compound in THF at 0° C, leads, after hydrolysis, to the expected methylidenic diols. These diols undergo double intramolecular iodoetherification promoted by a silver salt, to furnish the ...