Preparation of .beta.-lactam derivatives

A process for preparing a .beta.-lactam derivative of the formula:

• ##STR54## wherein R.sub.2 ' represents a hydrogen atom, an arylthio group, an arylsulfonyl group, an amino group, a lower alkoxycarbonylamino group, a haloalkoxycarbonylamino group or an amido group, R.sub.3 represents a hydrogen atom or a lower alkyl group, and R.sub.4 ' represents a carboxyl group;
• a lower alkoxycarbonyl group;
• an unsubstituted or substituted lower alkyl group wherein the substituent is a hydroxy group, an N-lower alkanoylamino group, a halogen atom, a cyano group, a nitro group, a lower alkoxycarbonyl group, a lower alkylcarbonyl group, an arylcarbonyl group or a gem-lower alkylenedioxy group or an unsubstituted or substituted lower alkenyl group wherein the substituent is a carboxyl group, a lower alkoxycarbonyl group, an aralkyloxycarbonyl group, a nitro group or an aryl group, which process comprises reacting a .beta.-lactam derivative of the formula ##STR55## wherein R.sub.1 represents a mono- or diarylmethyl group and R.sub.2 ', R.sub.3 and R.sub.4 ' are as defined above, with ceric ammonium nitrate having the formula Ce(NO.sub.3).sub.6 (NH.sub.4).sub.2 to cleave the bond between the nitrogen atom on said .beta.-lactam ring and the mono- or diarylmethyl group represented by R.sub.1.