The allenyl .beta.-lactam compound represented by the general formula (4) given below is conventionally prepared, for example, by reacting a tertiary organic base with the starting material in an organic solvent according to the process disclosed in JP-A-282359/1992. However, this compound is unstable when present in the resulting reaction mixture, which therefore usually requires cumbersome repeated procedures for extraction and concentration after the completion of the reaction. These procedures require time in the case of a large scale production, consequently entailing problems such as a marked reduction in the yield of the isolated product. Thus, processes still remain to be developed which are satisfactorily feasible for the preparation of allenyl .beta.-lactam compounds.
Reports have been made on widely acceptable processes for preparing 3-halogenated cephem derivatives represented by the general formula (6) given below. These processes include a process which uses a compound of the general formula (7), i.e., 3-hydroxycephem compound, as the starting material and involves the conversion of hydroxyl group to trifluoromesyloxy group first and the subsequent reaction with a lithium halide as described in J. Org. Chem., 54, 4962(1989), a process wherein a reactive chlorine or bromine compound (such as phosphorus trichloride, phosphorus oxychloride or thionyl bromide) is reacted with a 3-- hydroxycephem compound in dimethylformamide as disclosed in JP-A-116095/1974), and further a process wherein an alkali metal salt or alkaline-earth metal salt of a halogen is reacted with an allenyl .beta.-lactam compound as disclosed in JP-A-282387/1992 ##STR1## wherein R.sup.1, R.sup.2 and R.sup.3 are as defined below.
The first of the processes requires the use of the 3-hydroxycephem compound as the starting material which compound itself is difficult to prepare, so that the process is in no way practically feasible. The second process inevitably forms 3-sulfonylcephem or 3-thiocephem as a by-product due to the recombination of sulfinate ion or thiolate ion which is released on ring closure, consequently giving the desired 3-halogenated cephem derivative in a yield of as low as up to 70%.
An object of the present invention is to provide a process wherein a .beta.-lactam compound represented by the general formula (1) is used as the starting material for preparing an allenyl .beta.-lactam compound of the general formula (4) as isolated with stability and high purity in a high yield by a simplified procedure.
Another object of the invention is to overcome the drawbacks of the conventional production processes described and to provide a widely-useful process for preparing the desired 3-halogenated cephem derivative in a high yield with a high purity.