1: (6R-cis)-7-amino-3-lt;lt;(1-methyl-1H-tetrazol-5-yl)thiogt;methylgt;-7-(methylthio)-8-oxo-5-thia-1-azabicyclolt;4.2.0gt;oct-2-ene-2-carboxylic acid diphenylmethyl ester; diphenylmethyl (6R,7S)-7-amino-7-methoxy-3-lt;lt;(1-methyl-1H-tetrazol-5-yl)thiogt;methylgt;-Δ3-cephem-4-carboxylate; 2-bromo acetyl bromide With pyridine in dichloromethane T=-30 - -20°C; 1 h; 2: in dichloromethane; water T=0 - 5°C; 3: methanol With N-bromosuccinmide; sodium thiosulfate Purification / work up; more than 3 stages;