A STUDY OF THE REACTIONS OF N-METHYLNITRILIUM TRIFLUOROMETHANESULFONATE SALTS WITH BENZYLIDENETRIPHENYLPHOSPHORANE

Reactions between the N-methylnitrilium trifluoromethanesulfonate salt s [RC=NMe]+ OTf- (R = Ph, 2-MeC6H4, 4-MeC6H4, Me, Et, PhCH2, Pr and Pr (i); OTf = CF3SO3) and benzylidenetriphenylphosphorane (PhCH = PPh3) g ive, as the major product, the enaminophosphonium salts [Ph3PCPh = CRN HMe]+ X-, where X = OTf or Br depending upon the reaction conditions a nd work-up procedure. Spectroscopic data and a single crystal X-ray st ructure determination on the compound [Ph3PCPh = CPr(i)NHMe]+ Br- have shown that in all cases the major product has the E configuration abo ut the C = C bond and the Z configuration about the C-N bond, but the other possible stereoisomers are also present in minor amounts. When R = Bu(t) the product is the alpha-iminophosphonium salt [Ph3PCHPhCBu(t ) = NMe]+ OTf- and there was no evidence for the formation of an enami nophosphonium salt in this case.