Tautomerization of α,β-and β,γ-unsaturated phosphonium salts resulting from the reaction of triphenylphosphine with β-bromomethacrylic acid. Nucleophilic addition at the γ position of the allyl group in phosphonium salt

Abstract

Temperature factor was found to be determining in the isomerization of 2-carboxyprop-1-en-1-yl-and 2-carboxyprop-2-en-1-yl(triphenyl)phosphonium bromides. Elevated temperature favors formation of isomer with the double bond in the β,γ position with respect to the phosphonium group. Alkaline hydrolysis at room temperature promotes the reverse isomerization. The isomerization of 2-carboxyprop-1-en-1-yl(triphenyl)phosphonium bromide is hampered by addition of hydrobromic acid, as well as by carrying out its synthesis in the presence of aqueous HBr. Alkaline hydrolysis of 2-carboxyprop-1-enyl(triphenyl)phosphonium bromide and (E)-(2-carboxyvinyl)triphenylphosphonium chloride is accompanied by phenyl group migration to the α-position with formation of 2-methyl-3-(diphenylphosphoryl)-3-phenylpropionic acid and 3-(diphenyl-phosphoryl)-3-phenylpropionic acid, respectively. The possibility for nucleophilic addition at the γ position of the allyl group in 2-carboxyprop-2-enyl(triphenyl)phosphonium bromide was demonstrated using the reaction with triphenylphosphine as an example.