A study of the reactions of N-methylnitrilium trifluoromethanesulfonate salts with benzylidenetriphenylphosphorane

Abstract

Reactions between the N-methylnitrilium trifluoromethanesulfonate salts [RCN Me]⁺ OTf^–(R = Ph, 2-McC₆H₄, 4-McC₆H₄, Me, Et, PhCH₂, Pr and Pr¹ OTf = CF₃SO₃) and benzylidenetriphenylphosphorane (PhCHPPh₃) give, as the major product, the enaminophosphonium salts [Ph₃PCPhCRNHMe]⁺ X^–, where X = OTf or Br depending upon the reaction conditions and work-up procedure. Spectroscopic data and a single crystal X-ray structure determination on the compound [Ph₃PCPhCPrⁱNHMe]⁺ Br^– have shown that in all cases the major product has the E configuration about the CC 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 α-imino-phosphonium salt [Ph₃PCHPhCBu^tNMe]⁺ OTf^– and there was no evidence for the formation of an enaminophosphonium salt in this case.