A solution of 10 g of 3-formyl-7β-phenylacetylamino-ceph-2-em-4α-carboxylic acid in 250 ml of a 4:1 mixture of dioxane and methanol is treated with a solution of 1.5 mol equivalents of diphenyldiazomethane in cyclohexane. After 2 hours at room temperature, the red-violet solution is evaporated to dryness under reduced pressure. The residue is dissolved in hot methylene chloride; the solution is diluted with cyclohexane whilst warm, and 3-formyl-7β-phenylacetylamino-ceph-2-em-4α-carboxlic acid diphenylmethyl ester is obtained in practically quantitative yield in the form of fine colourless felted needles, melting point 175.5°-176° C. (uncorrected, decomposition); [α]D20 =+513°±1° (c=1,084 in chloroform); thin layer chromatogram (silica gel): Rf=0.35 (system: toluene/acetone, 80:20) and Rf=0.58 (system: toluene/acetone 65:35); ultraviolet absorption spectrum (in 95% ethanol): λmax =289 mμ (ε=20,200) and λmin =245 mμ (ε= 2,100); infrared absorption spectrum: characteristic bands at 2.92μ, 3.53μ, 5.59μ, 5.72μ, 5.91μ, 6.34μ, 6.61μ and 6.67μ (in methylene chloride) and at 3.00μ, 5.63μ, 5.76μ, 5.95μ (double band), 5.99μ, 6.07μ and 6.58μ (in mineral oil).
