Do reactions of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane require fluoride anion catalysis?

Abstract

Abstract 2,2,4,4-Tetrakis(trifluoromethyl)-1,3-dithietane (cyclic dimer of hexafluorothioacetone (1)) was shown to react with a variety of organic substrates in the absence of metal fluoride catalyst at elevated temperature in DMSO or DMF solvents. While the reactions of vinyl ethers, phenyl vinyl sulfide, dienes and anthracenes under these conditions led to the formation of expected cycloadducts, the reaction of 1,5-cyclooctadiene resulted in the formation of the product derived from an ene reaction with hexafluorothioacetone (HFTA). In contrast to results reported for the CsF catalysed process, 2-vinylnaphthalene reacted with 1 to produce a compound that resulted from reaction with two molecules of HFTA. The structure of this adduct was established using single crystal X-ray diffraction. The formation of similar products was also observed in non-catalysed reactions of styrene and 2-methylstyrene with 1. Interestingly, no product of this type was observed in reaction of 4-MeO-styrene with 1, which instead led to the high yield formation of the corresponding thietane. The reaction of 1 with 1,3-cyclohexadiene was carried out in various organic solvents: the reaction in DMSO and DMF was significantly faster than in acetonitrile, tetrahydrofurane or hexane.