Fluorinated thietanes

F-(2,2,4,4-Tetrakis(trifluoromethyl)thietane is the only known example of per-fluorinated thietanes. It can be prepared by high-yield reaction of (CF3)2C=Cp2 with sulfur, catalyzed by CsF. First perfluorinated thiete was prepared by the reaction of hexafluorpropene trimer with (CH3)3CSH and later by dehydrofluorination of unsaturated thiol [(CF3)2CF]2C=C(SH)CF3 (X=H). The hydrolysis of sulfenul chloride [(CF3)2CF]2C=C(SC1)CF3 afforded perfluorinated thiete oxide. ... 

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... 

SCHEME 2.23 Reductive ring expansion of fluorinated thietanes. 

Sanin etal. described the reaction of a,/3-unsaturated fluorinated ketones 88 with ammonium sulfide in ethanol, which led to the formation of thiopyran- Wdioxide derivatives 89 (Equation 28) <1996JOC1986>. However, one of the studied ketones (3-adamantan-2-ylidene-l,l,l-trifluoro-propan-2-one 90) demonstrated an unusual behavior in the course of this reaction, which led to the formation of the fused-ring thietane 31 in 86% yield (Equation 29) <1996JOC1986>. 

Treatment of thietane with chlorine, bromine,or sulfuryl chloride yields ring-opened materials. Trifluoromethyl hypofluorite gives tetravalent and hexa-valent sulfur-fluorine compounds 86 (a sulfurane) and 87 (a persulfurane) from thietane and 3-methylthietane. Ionization of 86 (R = H) at —20° to — 40°C was indicated by the collapse of the two doublets observed in the F nmr spec-... 

Petrov, V.A. Abstracts of 15th European Symposium on Fluorine Chemistry, Prague, Czech Republic, July 15-20, 2007, p 161. (a) Petrov, V.A. Marshall, W.J. Reactions of Polyfiuorinated Thietanes. Selective Synthesis of Polyfluorinated Thietanes S-Oxides and 2-Substituted 5-fiuoro-4-(trifiuoromethyl)-2,3-dihydrothiophenes, J. Fluorine Chem. 2009, doi 10.1016/j.jfiuchem.2009.06.011. 

Five-membered fluorine-containing heterocyclic compounds with two or three sulfur atoms are more extended. A ring expansion reaction of thietanes into 1,2-dithiolanes involving heating with sulfur was used. ... 

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