CF3 Oxonium Salts, O-(Trifluoromethyl)dibenzofuranium Salts: In Situ Synthesis, Properties, and Application as a Real CF3+ Species Reagent

• DOI: 10.1021/jo070896r
• Publication Date: 2007-08-04T17:00:53Z
• Authors: Teruo Umemoto; Kenji Adachi; Sumi Ishihara
• Keywords: Oxonium ion; Sodium salt

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