Electrochemical Reformatsky reaction of α-haloketones and benzaldehyde on a graphite powder cathode free of organic solvents

Six α-haloketones adsorbed on a graphite powder cathode were reduced in the presence of benzaldehyde using undivided cell, inert anode and aqueous electrolyte. High yields of aldol coupling product were obtained from 2-chloropinacolone in the presence of catalytic amounts of silver. For the corresponding bromo compound, the reaction was much less satisfactory. Chloroacetone gave moderate yields of the α,β-unsaturated coupling product. 2-Chlorobutanone produced two main products in low yield: the expected aldol and the corresponding 1,3-diketone. With 2-bromopropiophenone and 2-bromoisobutyrophenone no coupling with benzaldehyde was observed but only reductive dehalogenation. The results can be interpreted in terms of a carbanionic intermediate generated by a two-electron transfer.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Six α-haloketones in presence of benzaldehyde were reduced on a graphite powder/silver (98:2) electrode. ► 1-chloropinacolone resulted in high yields of aldol, but the corresponding bromo compound was not satisfactory. ► Chloroacetone gave moderate yields of the α,β-unsaturated coupling product. ► 3-Chloro-2-butanone produced low yield of aldol and the corresponding 1,3-diketone. ► With 2-bromopropiophenone and 2-bromoisobutyrophenone no coupling with benzaldehyde was observed.