Vinylphosphonium salts, aromatic

Diarylpyrroles have been constructed from a-amidonitriles and vinylphosphonium salts. The reaction presumably proceeds by nucleophilic addition to the vinylphosphonium salt followed by cyclization via an intramolecular Wittig reaction. Elimination of HCN accounts for the final aromatization (equation 118) (81JOC2570). 

Michael addition of l-lithio-2-methoxycarbonylprop-2-enyl phenyl sulphide to acrylates gives 3-(phenylthio)cyclopentadienones, while addition to aldehydes is followed similarly by cyclization to furan-2-ones. Further uses of vinyl sulphides in syntheses of cyclic compounds include an efficient pentannelation procedure (Scheme 12), cyclization of )i (3-phenylthio-2-methylprop-2-enyl)-)ff-keto-esters to 3-(phenylthio)cyclohexanones, using TFA, and an aromatic substitution reaction [HOCPhjCCSEt)—CHj - 3-phenyl-2-(ethylthio)indene] that involves attack at the yff-carbon atom of the vinyl sulphide moiety, promoted by acid-catalysed dehydration. l-(Phenylthio)vinylphosphonium salts PhSC(=CH PPh3 X , have been advocated for use in the synthesis of cyclopentanone by condensation with... 

The mechanism of formation of aromatic vinylphosphonium salts via the Peterson olefination has been investigated. It has been found that the electronic nature of p-substituents in aromatic aldehydes strongly influences the stereochemical and kinetic outcome of the Peterson olefination, whereas temperature substantially affects their Hammett correlation. This indicates that the Peterson olefination is a multistep reaction involving the formation of at least an oxyanion/betaine and a carbanion as intermediates. 

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