Tetrahydrofuran → Benzyl alpha-[3-phenoxymethyl-7-oxo4-thia-2,6-diazabicyclo[3,2,0]hept-2-en-6-yl]-alpha-(methanesulfonyloxyethylidene)acetate

One adds triethylamine (1.42 ml), and methanesulfonyl chloride (0.41 ml) to a solution of benzyl α-[3-phenoxymethyl-7-oxo-4-thia-2,6-diazabicyclo[3,2,0]hept-2en-6-yl]-α-(1-hydroxyethylidene)acetate (2.12 g) in tetrahydrofuran (30 ml) at -30° C., stirs for 70 minutes to give benzyl α-[3-phenoxymethyl-7-oxo-4-thia-2,6-diazabicyclo[3,2,0]hept-2-en-6-yl]-α-(methanesulfonyloxyethylidene)acetate, adds morphline (0.6 ml) and stirs for 4 hours 50 minutes at 0° C. to give benzyl α-[3-phenoxymethyl-7-oxo-4-thia-2,6-diazabicyclo[3,2,0]hept-2-en-6-yl]-α-(1-morpholinoethylidene)acetate, cools to -50° C., adds pyridine (0.385 ml) and bromine (0.25 ml), and stirs for 30 minutes to give benzyl α-[3-phenoxymethyl-7-oxo-4-thia-2,6-bicyclo[3,2,0]hept-2-en-6-yl]-α-(1-morpholino-2-bromoethylidene)acetate, adds 5% hydrochloric acid (36 ml), methanol (42.5 ml), and tetrahydrofuran (12.5 ml) to give clear solution. The solution is concentrated, the resulting solution being extracted with ethyl acetate, washed with saturated saline, dried over sodium sulfate, and concentrated to give residue (2.31 g). Purification of the residue by chromatography over silica gel containing 10% water gives benzyl 7β-phenoxyacetamido-3-hydroxy-3-cephem-4-carboxylate (1.11 g). m.p. 126°-127° C.