For this reason, document (4) cannot be considered as the closest state of the art (cf. point 4.3 above).4.3.4 Document (5) discloses a process consisting in chlorinating, in the presence of a chlorinating agent such as phosgene and phosphorus pentachloride, acyl cephalosporins of the formula (i)FORMULA/TABLE/GRAPHICwherein Z isFORMULA/TABLE/GRAPHICwherein R is readily removable carboxy protecting