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.