The prototropic equilibria in pentenylphosphonic systems

Abstract

Dialkyl 2-chloropentylphosphonates, C3H7CHClCH2P(O)(OR)2, and monoalkyl 2-chloropentylphosphonic acids, C3H7CHClCH2PO2H(OR), have been dehydrohalogenated by strong bases to the corresponding pentenylphosphonic compounds. In all cases the kinetically controlled product was shown to be the E-1-pentenylphosphonic derivative. The α,β-unsaturated products underwent base-catalysed isomerization to the thermodynamically controlled E-2-pentenylphosphonic systems, thus indicating that the PO3R2 and PO3R− groups destabilize (relative to hydrogen) the adjacent olefinic bond. The hydrogen–deuterium isotope exchange was studied for the α,β- and β,γ-unsaturated products and the results obtained were in full agreement with the isomerization results.