Remarkable effect of metal fluoride catalyst on reaction of hexafluoropropene, sulfur and vinyl ethers. Convenient synthesis of 2,2-bis(trifluoromethyl)-4-R-thietanes, 3,3-bis(trifluoromethyl)-5-R-1,2-dithiolanes and 2,2-bis(trifluoromethyl)-4-R-1,3-dithiolanes

Abstract

It was demonstrated that the outcome of the reaction of hexafluoropropene, sulfur and vinyl ether strongly depends on the catalyst and reaction conditions. The reaction of HFP and S x leading to the formation of 2,2,4,4-tetrakis(trifluoromethyl)-1,3-dithietane ( 1) when it is catalyzed by CsF, proceeds under milder conditions and is easier to control compared to KF catalyzed process. The order of addition of reagents plays a crucial role on the outcome of the reaction. For example, the addition of vinyl ether to pregenerated solution of 1 in DMF solvent results in slow reaction, leading to the corresponding 2,2-bis(trifluoromethyl)-4-R-thietanes in 8–91% yield, and it is catalyzed by either by KF or CsF. The addition of second mole of sulfur to the solution of 2,2-bis(trifluoromethyl)-4-R-thietanes in the presence MF catalyst leads to insertion of sulfur into thietane ring with the formation of the corresponding cyclic disulfides—3,3-bis(trifluoromethyl)-5-R-1,2-dithietanes. On the other hand, the addition of second mole of sulfur to the solution of 1 in DMF in the presence of CsF catalyst, followed by addition of vinyl ether results in exothermic reaction, and it produces the corresponding 2,2-bis(trifluoromethyl)-4-alkoxy-1,3-dithiolanes in good yield. It was also demonstrated that 2,2-bis(trifluoromethyl)-4-R-thietanes can undergo disproportionation under action of fluoride anion, producing a mixture of the corresponding 1,2-dithiolane and CF 2 C(CF 3)CH 2CFHOR. The nucleophilic attack of fluoride anion in this case proceeds selectively on the carbon of the thietane ring, bearing alkoxy group. The structure of 2,2-bis(trifluoromethyl)-4-R-thietanes forming as the result of 2 + 2 cycloaddition reaction between hexafluorothioacetone generated “in situ” from dimer 1 and vinyl ether was firmly supported by single crystal X-ray diffraction data, obtained for thietane bearing t-BuO-group.