A compound represented by the formula ##STR1## wherein R.sub.1 represents a lower alkyl group or a lower haloalkyl group; R.sub.2 represents a lower alkyl group, a lower haloalkyl group, an aralkyl group, or a group of the formula --COOR.sub.4 or --SO.sub.2 R.sub.5 in which R.sub.4 represents an alkyl group or a substituted or unsubstituted aralkyl group and R.sub.5 represents an alkyl group or a substituted or unsubstituted aryl group; and R.sub.3 represents a hydrogen atom or a carboxyl protecting group which can be easily split off. This compound is useful in the production of a 6-(disubstituted amino)carbapenem-series antibiotic.