Preparation of 3-substituted cephalosporins

A process for preparing an enamine of formula (IX):

• ##STR19## where R.sup.2 is a carboxylic acid protecting group and R.sup.3 is the residue of a carboxylic acid derived acyl group and where R.sup.5 and R.sup.6 are the same or different C.sub.1-4 alkyl or C.sub.7-10 aralkyl groups;
• or taken together with the ajacent nitrogen atom form a heterocyclic ring containing from 4 to 8 carbon atoms and optionally a further heteroatom selected from oxygen and nitrogen;
• by reacting an enol of formula (XI):
• ##STR20## with a phosphorus reagent of formula (VII):
• ##STR21## where R.sup.a and R.sup.b are the same or different and can each represent phenyl or phenoxy optionally substituted by one to three groups selected from C.sub.1-4 alkyl, C.sub.1-4 alkoxy, halogen and nitro;
• or is C.sub.1-4 alkyl, C.sub.1-4 alkoxy, C.sub.3-8 cycloalkyl, C.sub.3-8 cycloalkoxy, chlorine or bromine;
• X is chlorine, bromine, nitrile or azide;
• provided that:
• (i) R.sup.a and R.sup.b cannot both be halogen;
• and
• (ii) when X is nitrile or azide, R.sup.a and R.sup.b are the same or different phenoxy;
• C.sub.3-8 cycloalkoxy or C.sub.1-4 alkoxy groups, to form a product of formula (XII):
• ##STR22## followed by reaction of this product with an amine of formula HNR.sup.5 R.sup.6 to form the enamine of formula (IX).