Mechanistic investigation of the iron-mediated electrochemical formation of β-hydroxyesters from α-haloesters and carbonyl compounds

The electrochemical behavior of FeI in the presence of α-haloesters has been studied by means of cyclic voltammetry and preparative-scale electrolyses with the intent to investigate the electrochemical coupling reaction between α-haloesters and carbonyl compounds performed in the presence of FeBr2 and a sacrificial iron anode. It is established that the reaction is initiated by the electrogeneration of an iron (I) species, which has to be stabilized by the presence of 2,2′-bipyridine (bpy). However, the reactivity of the electrogenerated FeI is governed by the bpy concentration. Indeed, for bpy/Fe ratios higher than or equal to 3, an outer-sphere electron transfer has been shown between FeI and α-haloesters, but no coupling product was obtained under these conditions. Conversely, for smaller bpy/Fe ratios the coupling reaction occurs, suggesting the existence of an oxidative addition between FeI and α-haloesters. The presence of a sacrificial iron anode in preparative-scale experiments is useful to decrease the bpy/Fe ratio by generation of Fe2+ cations.