Protected aminothiazolylacetic acid derivatives

A process for the preparation of a protected aminothiazolylacetic acid derivative or a salt thereof, said protected aminothiazolylacetic acid derivative represented by the following formula (I):

• ##STR27## wherein A represents a nitrogen atom or a methine group, R.sup.1 and R.sup.2 may be the same or different and individually represent a hydrogen atom, a lower alkyl group or a substituted or unsubstituted aryl group, R.sup.3 represents a lower alkoxy group, a halogenated lower alkoxy group, a triphenylmethoxy group, a lower alkyl group or an acyloxy group, and R.sup.4 represents a halogen atom, a hydroxy group, a lower alkoxy group or a substituted or unsubstituted amino group, or a salt thereof, which process comprises:
• reacting an aminothiazolylacetic acid derivative represented by the following formula (II):
• ##STR28## wherein A, R.sup.3 and R.sup.4 have the same meanings as defined above, or a salt thereof, with a (halogenated methylene)-dialkylammonium halide represented by the following formula (III):
• ##STR29## wherein R.sup.1 and R.sup.2 have the same meanings as defined above and X represents a halogen atom.