Electrochemistry of some ethyl α-bromo(dihalophenyl) acetates and electrochemical synthesis of diastereoisomeric diethyl 2,3-bis (dihalogenophenyl) succinates

Abstract

Ethyl α-bromo-2,4- or -3,4-dihalogenophenylacetates (ABr), where halogen = F or Cl, are prepared and electrolysed on reticulated vitreous carbon (RVC) in dimethylformamide containing Et₄NClO₄(0.1 mol dm^–3). Potentiostatic reduction at E=–1.6 to –1.8 V versus SCE furnishes the corresponding racemic and meso succinates (AA)(13)–(16). Monoesters AH (5)–(8) are also isolated. An excess pf racemic isomer is observed for (14), (15), and (16). Voltammetric experiments show practically no difference between the reduction potentials of the isomeric compounds. Diastereoisomers can be distinguished by NMR spectroscopy, allowing diastereoisomeric excess (de) to be evaluated before isolation of the single products. A mechanism involving radical intermediates A˙ cannot be excluded. On this basis, the des can be explained by assuming different geometries for A˙ when the phenyl group bears different substituents.