Fluorinated dithietanes synthesis

Thiocarbonyl fluoride, 9, is prepared in good yield by pyrolysis of 6 at ca. 600°C in the vapor phase or by carrying out the reaction of sulfur and tetrafluoroethylene at higher temperatures. A cleaner synthesis involves fluorination of thiophosgene dimer to tetrafluoro-l,3-dithietane, 10, followed by cracking of 10 to two molecules of 9 (7). 

Rail, K. Sundermeyer, W. Synthesis of perhalogenated 1,3-dithietane 5-oxides and thiiranes. J. Fluorine Chem. 1990, 47, 121. 

Since the simplest F-l,3-dithietane (38) cannot be prepared by dimerization of thiocarbonyl fluoride, probably due to propensity of the latter to polymerize, a different synthetic approach is employed for its synthesis. Two-step process includes photocyclodimerization of Cl2C=S and Swarts-type fluorination of the dimer by antimony trifluoride to give 38 (Scheme 2.20). Compound 38 can be a source of very pure thiocarbonyl fluoride, when pyrolyzed at 500°C." ... 

Synthetic applications of dithietane 35 are not limited to its use as a source of hexafluorothioacetone. This compound is also a valuable precursor for the synthesis of a variety of fluorinated sulfur-containing derivatives. For example, the pyrolysis of 35 at 325 C results in the high-yield formation of (CF3)2C=C(CF3)2. The reaction of 35 with PhaP was found to be a convenient route to (Ph)3P=C(CF3)2, which was used for the preparation of l,l-bis(trifluoromethyl) alkenes and CF2=C(CF3)P(0)(0R)2. Recently reported transformation of fluorinated thietanes involves reductive ring expansion to substituted dihydrothiophenes. For example, the treatment of compound 47 with aluminum powder in the presence of a catalytic amount of PbCl2 resulted in an interesting ring expansion process leading to the formation of compound 48 in excellent yield (Scheme 2.23). Readily available fluorinated cycloadducts 49... 

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See also in sourсe #XX -- [ , , ]

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