To a cooled (-73° C.), stirred solution of 1.559 g. of benzhydryl 7-(2-thienylacetamido)-3-formyl-2-cephem-4-carboxylate and 20 ml. of dry tetrahydrofuran was added 3.13 ml. of 2.88 M. ethyl magnesium bromide. After the reaction mixture was allowed to stir for four minutes at -73° C., 10 ml. of 1N.HCl was added and the solution allowed to warm to 0° C. The reaction mixture was transferred to a separatory funnel with the aid of cold ethyl acetate and cold 1N.HCl. The organic layer was separated and washed twice with cold 1N.HCl and twice with brine and then dried over anhydrous sodium sulfate. Evaporation in vacuo to dryness provided a product residue which was chromatographed on silica gel using a toluene-ethyl acetate gradient to give 0.140 g. of the starting 3-formyl-2-cephem ester and 0.507 g. (30.6 percent) of the title product as a mixture of diasteromers:
