ZnCl-mediated stereo- and chemoselective synthesis of vinylphosphonates.

A highly chemo- and stereoselective synthesis of diethyl ()-2-(alkylidene)-2-phosphonoacetonitriles the Knoevenagel condensation reaction of carbonyl compounds with diethyl cyanomethylphosphonate in the presence of zinc chloride has been achieved. By the presented method, various -isomers of arylmethylidene phosphonates rather than Horner-Wadsworth-Emmons olefination products were obtained in good to excellent yields. Their configurations were determined by X-ray diffraction and NMR analyses. In addition, DFT calculations provided insights into the chemo- and stereoselectivity of the reaction.