Process for preparing 7-methoxycephalosporin compounds

A process for preparing a 7.alpha.-methoxy-3-cephem-4-carboxylic acid having the formula ##STR40## wherein R represents cyanomethylthio, 1-cyanoethylthio, azidomethylthio, propargylthio, 2-hydroxyethylthio, 2,3-dihydroxypropylthio, methylsulfonyl, ethylsulfonyl, cyanoethylsulfonyl, 3-isoxazolyloxy, 3-isoxazolylthio, 2-(1,3,4-thiadiazolyl)thio, 2-imidazolythio or sydnon-3-yl nd R.sup.1 is acetoxy, carbamoyloxy or 1-methyl-1H-tetrazol-5-ylthio or a salt with the carboxyl group thereof which comprises the steps of contacting a 7.beta.-benzylidenemino-7.alpha.-methoxy-3-cephem-4-carboxylic acid having the formula ##STR41## wherein R.sup.1 is the same as defined above, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 may be the same or different and each represents hydrogen atom, an alkyl having 1-4 carbon atoms, an alkoxy having 1-4 carbon atoms, or a halogen atom, or R.sup.2 and R.sup.3 or R.sup.4 and R.sup.5 may be linked together to form a saturated, unsaturated or aromatic ring, n is an integer of 1 or 2 and Y.sup.+ is a cation selected from the group consisting of an alkali metal ion and an ammonium ion having the formula ##STR42## wherein R.sub.a, R.sub.b, R.sub.c and R.sub.d can be the same or different, and each is selected from the group consisting of hydrogen alkyl having from 1 to 8 carbon atoms, cyclopentyl, cyclohexyl, cycloheptyl, phenyl, phenylalkyl wherein the alkyl has from 1 to 4 carbon atoms, R.sub.a and R.sub.b can be linked together with said N to form a saturated heterocyclic ring, and R.sub.a, R.sub.b and R.sub.c can be linked together with said N to form a heterocyclic ring, with a hyrazine to give a 7-amino-7-methoxy-3-cephem-4-carboxylic acid having the formula ##STR43## wherein R.sup.1 and Y.sup.+ are the same as defined above, and reacting the latter compound with a compound selected from the group consisting of a carboxylic acid having the formula

• RCH.sub.2 COOH (IV)
• wherein R is the same as defined above, an acid halide of (IV), an azide of (IV), an acid anhydride of (IV), a p-nitrophenyl ester of (IV), cyanomethyl ester of (IV) and a phthalimide ester of (IV).