To a solution of 3-methanesulfonyloxy-7beta-phenylacetylaminocepham-4-carboxylic acid diphenylmethyl ester (3c) in dichloromethane (7 parts) cooling at -25° to -20° C. under nitrogen are added pyridine (2 equivalents) and phosphorus pentachloride (1.7 equivalents). After stirring at -15° to -10° C. for 4 hours, the mixture is diluted with methanol (12 parts) cooled at -40° to -30° C. After stirring for 30 minutes at -30° C. and for 2.5 hours at 0° to 5° C., the mixture is cooled to -30° C., mixed dropwise with triethylamine (8.1 equivalents) and let stand overnight at 0° to 5° C. The mixture is diluted with dichloromethane and ice-water and stirred for 20 minutes at 0° to 5° C. The formed organic layer is taken, washed with hydrochloric acid, water, aqueous sodium hydrogen carbonate, and water, dried, and concentrated. The residue is crystallized from ethyl acetate to give 7beta-amino-3-cephem-4-carboxylic acid diphenylmethyl ester (5). Yield: 55.7%.
