Ethyl-2-(chloromethyl)-acrylate (3.86 g, 26.0 mmol, 1.5 eq.) was added to a solution of 2-hydroxymethyl-1,3-propylene-bisphosphonic acid tetraethylester (6.0 g, 17.3 mmol) and triethylamine (3.62 ml, 26 mmol, 1.5 eq.) in anhydrous THF (30 ml), and the reaction mixture was stirred for 45 h at 70° C. After concentrating in vacuo deionized water (50 ml) was added and the obtained solution was extracted with ethylacetate (3×50 ml). The combined organic phases were dried with anhydrous sodium sulphate. After removal of the solvent under reduced pressure the obtained crude product was purified by column chromatography (eluent: ethylacetate/methanol 98:2). 3.77 g (48% yield) of the product was obtained as a yellowish oil.
