Tetraethyl (phenoxymethylene)-bisphosphonate (1.14 g) was added to a suspension of 55% sodium hydride (0.15 g) in dimethylformamide (10 ml). After 45 minutes at room temperature, ethyl iodide (0.49 ml) was added, and the mixture was left overnight at room temperature, diluted with ethyl acetate and washed with 40% aqueous calcium chloride. The organic phase was dried and evaporated to leave an oil which was purified by chromatography on silica gel. The title compound was isolated as a colourless oil.
