for the following products
(6b)-3-(1-Methyl-1H-tetrazole-5-ylthiomethyl)-7a-amino-7-methoxy-8-oxo-5-oxa-1-azabicyclo[4.2.0]octa-2-ene-2-carboxylic acid benzhydryl ester and (6R,7R)-7-Amino-7-methoxy-3-[(1-methyl-1H-tetrazol-5-ylthio)methyl]-8-oxo-5-oxa-1-azabicyclo[4.2.0]oct-2-ene-2-carboxylic acid diphenylmethyl ester
