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Versatile, safe, shelf-stable, and easy-to-handle fluorinating agents are strongly desired in both academic and industrial arenas, since fluorinated compounds have attracted considerable interest in many areas, such as drug discovery, due to the unique effects of fluorine atoms when incorporated into molecules. This article describes the synthesis, properties, and reactivity of many substituted and thermally stable phenylsulfur trifluorides, in particular, 4-tert-butyl-2,6-dimethylphenylsulfur trifluoride (Fluolead, 1k), as a crystalline solid having surprisingly high stability on contact with water and superior utility as a deoxofluorinating agent compared to current reagents, such as DAST and its analogues. The roles of substituents on 1k in thermal and hydrolytic stability, fluorination reactivity, and the high-yield fluorination mechanism it undergoes have been clarified. In addition to fluorinations of alcohols, aldehydes, and enolizable ketones, 1k smoothly converts non-enolizable carbonyls to CF(2) groups, and carboxylic groups to CF(3) groups, in high yields. 1k also converts C(=S) and CH(3)SC(=S)O groups to CF(2) and CF(3)O groups, respectively, in high yields. In addition, 1k effects highly stereoselective deoxofluoro-arylsulfinylation of diols and amino alcohols to give fluoroalkyl arylsulfinates and arylsulfinamides, with complete inversion of configuration at fluorine and the simultaneous, selective formation of one conformational isomer at the sulfoxide sulfur atom. Considering the unique and diverse properties, relative safety, and ease of handling of 1k in addition to its convenient synthesis, it is expected to find considerable use as a novel fluorinating agent in both academic and industrial arenas.

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We report in situ synthesis of the first CF(3) oxonium salts, thermally unstable O-(trifluoromethyl)dibenzofuranium salts, which furthermore have different counteranions (BF(4)-, PF(6)-, SbF(6)-, and Sb(2)F(11)-) and ring substituents (tert-butyl, F, and OCH(3)), by photochemical decomposition of the corresponding 2-(trifluoromethoxy)biphenylyl-2'-diazonium salts at -90 to -100 degrees C. The yields markedly increased in the order of BF(4)- < PF(6)- < SbF(6)- < Sb(2)F(11)-. The CF(3) oxonium salts were fully assigned by means of (1)H and (19)F NMR spectroscopy at low temperature. The CF(3) salts decomposed to form CF(4) and dibenzofurans. The half-life times at -60 degrees C of the 2-tert-butyl salts having different counteranions were 29 min for BF(4)- salt 2d, 36 min for PF(6)- salt 2c, 270 min for SbF(6)- salt 2a, and 415 min for Sb(2)F(11)- salt 2b. Those at -60 degrees C of the Sb(2)F(11)- salts having different 2-substituents were 13 min for F salt 3b, 63 min for H (unsubstituted) salt 1b, and 415 min for tert-butyl salt 2b. Thus, the stability of the CF(3) oxonium salts increased in the order of BF(4)- < PF(6)- < SbF(6)- < Sb(2)F(11)- and F < H < tert-butyl, which is in accord with the increasing orders of the non-nucleophilicity of counteranions and the electron-donating effect of ring substituents. 2-tert-Butyl-O-(trifluoromethyl)dibenzofuranium hexafluoroantimonate (2a) was thus chosen and successfully applied as a real CF(3)+ species source to the direct O- and N-trifluoromethylations of alcohols, phenols, amines, anilines, and pyridines under very mild conditions. The thermal decomposition method with a mixture of diazonium salt 17a and aryl- or alkylsulfonic acids, pyridine, or pyridines having an electron-withdrawing group also afforded CF(3)O or CF(3)N products. The trifluoromethylation mechanism is discussed and an S(N)2 mechanism containing the transient formation of free CF(3)+ is proposed. Thus, the present study has demonstrated that the exceedingly reactive CF(3)+ species can be generated much easier than the CH(3)+ species, contrary to the common sense that CF(3)+ is extremely difficult to generate in solution.