Pyrolysis of (2-Phenylethyl)phenylsulfonium Ylides

Article abstract of DOI:10.1246/bcsj.66.174

In order to obtain information concerning the reaction mechanism of the pyrolysis of sulfonium ylides bearing a substituted phenyl group on the 2-position in the S-ethyl group of ethylphenylsulfonium ylide, (2-phenylethyl)phenylsulfonium bis(methoxycarbonyl)methylide (1) and dicyanomethylide(2) were subjected to pyrolysis in benzene.The reaction rates of 1 and 2 at 140 deg C were 6.0- and 3.2-times faster than those of ethylphenylsulfonium bis(methoxycarbonyl)methylide and dicyanomethylide, respectively.The activation parameters for 1 were ΔH⁺⁺=125 kJ mol^-1 and ΔS⁺⁺=-3.8 JK^-18mol^-1, while those for 2 were ΔH⁺⁺=124 kJ mol^-1 and ΔS⁺⁺=-2.5 JK^-1 mol^-1.Substituent efects on the β-phenyl groups in 1 and 2 afforded positive Hammett ρ-values: ρ = 0.49 (γ = 0.997) and ρ = 0.26 (γ = 0.993), respectively.From the obtained results, it was suggested that the pyrolysis proceeds through essentially a concerted intramolecular cis-elimination inclined toward a slightly carbanion-like type from an E1-like type by introducing a phenyl substituent at the 2-position of the ethyl group in the ethylphenylsulfonium ylide.