The chemistry of nitrilium salts. Part 2. The preparation of nitrilium trifluoromethanesulphonate salts and their reactions with some oxygen and sulphur nucleophiles

Abstract

The syntheses of the nitrilium salts [RCNMe]⁺Ō₃SCF₃[R = Me, Prⁱ, PhCH₂, Ph, CH₂CHCH₂, NC(CH₂)₃, and CH₂CH] by reaction of MeO₃SCF₃ with the corresponding nitriles are described. The similar reaction between (E)-PhCHCHCN and MeO₃SCF₃ gives a mixture of [(E)-PhCHCHCNMe]⁺Ō₃SCF₃ and the s-triazinium salt [{(E)-PhCHCH}₃C₃N₃H]⁺Ō₃SCF₃, which hydrolyzes to give (E)-PhCHCHCONHMe and the triazine. The compound CF₃SO₃(CH₂)₄CN, prepared from I(CH₂)₄CN and AgO₃SCF₃, does not form a cyclic nitrilium salt, but slowly dimerizes at room temperature to [CF₃SO₃(CH₂)₄CN(CH₂)₄CN]⁺Ō₃SCF₃. Both I(CH₂)₄CN and CF₃SO₃(CH₂)₄CN can be converted into the salt [CF₃SO₃(CH₂)₄CNMe]⁺Ō₃SCF₃, but this does not form a dinitrilium salt on reaction with acetonitrile. On heating benzophenone oxime with CF₃SO₃H Beckmann rearrangement products are obtained, but conversion of [MeC(OH)NHPh]⁺Ō₃SCF₃ into the nitrilium salt [CH₃CNPh]⁺Ō₃SCF₃ occurs in only low yield even after 8 h at 130 °C under high vacuum. The nitrilium salts with R = Ph, Me, Prⁱ, and PhCH₂ undergo rapid exothermic reactions with phenol, thiophenol, alcohols, and thiols to give the corresponding imidate and thioimidate salts in high yields. 4,4-Dimethyl-2-phenyl-1,3-oxazoline is obtained in 74% yield on heating [PhCNMe]⁺Ō₃SCF₃ with H₂NCMe₂CH₂OH, and both this and 2,4,4-trimethyloxazoline react with MeO₃SCF₃ to give almost quantitative yields of the corresponding N-methyloxazolinium salts, which can be reduced to the oxazolidines with NaBH₄. N-Methyloxazolinium salts have also been obtained from the reactions of nitrilium salts (R = Ph or Me) with ethylene oxide.