1,5-Diazabicyclo(5,4,0)undec-5-ene → 7beta-Phenoxyacetamido-3-methoxy-ceph-2-em-4-carboxylic acid diphenylmethyl ester

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A solution of 367 mg (0.5 mM) of a mixture consisting of 2-[4-(p-nitrobenzenesulphonylthio)-3-phenoxyacetamido-2-oxoazetidin-1-yl]-3-methoxy-crotonic acid diphenylmethyl ester and the corresponding isocrotonic acid diphenylmethyl ester, and 152 mg (1.0 mM) of 1,5-diazabicyclo[5.4.0]undec-5-ene in 10 ml of dry tetrahydrofurane is stirred for 40 minutes at room temperature. The reaction mixture is diluted with benzene, washed successively with dilute hydrochloric acid, water and dilute aqueous sodium bicarbonate solution, dried over sodium sulphate and freed from the solvent in vacuo. The residue is chromatographed on acid-washed silica gel, using toluene/ethyl acetate, 7:1, as the running agent, whereby pure 7β-phenoxyacetamido-3-methoxy-ceph-2-em-4-carboxylic acid diphenylmethyl ester is obtained. Subsequent elution with toluene/ethyl acetate, 2:1, results in the isolation of a mixture which in addition to 7β-phenoxyacetamido-3-methoxy-ceph-2-em-4-carboxylic acid diphenylmethyl ester also contains 7β-phenoxyacetamido-3-methoxy-ceph-3-em-4-carboxylic acid diphenylmethyl ester.

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