Abstract: The process for preparing cephalosporanic acid derivatives ##STR1## and salts thereof with bases as well as solvates thereof, comprising reacting a compound of the formula II: ##STR2## wherein R.sub.3 represents hydrogen or an amino protecting group and R.sub.2 represents hydrogen, an easily removable ester group or other carboxyl protecting group, with a compound of formula IIIa, ##STR3## wherein R.sub.1 represents hydrogen, an easily removable ester group or other carboxyl protecting group, and R.sub.4 is a 2-benzothiazol group and salts thereof with bases, and if required removing any ester group or protecting group.