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 = But the product is the α-imino-phosphonium salt [Ph3PCHPhCButNMe]+ OTf– and there was no evidence for the formation of an enaminophosphonium salt in this case.