Symmetrical azetidinone aldehyde disulfides and process

A process for preparing symmetrical azetidinone aldehyde disulfide compounds of the formula ##STR41## which comprises:

• (1) reacting a 2.alpha.-alkoxy cephalosporin ester of the formula ##STR42## with about 1 to about 1.3 equivalents of an N-chloro halogenating agent in a chlorinated hydrocarbon solvent at a temperature between -10.degree. C. and 30.degree. C.;
• (2) combining the above solution with an aqueous suspension of between about 2 and about 4 molar equivalents of mercury dichloride and about 5 to about 7 molar equivalents of cadmium carbonate at a temperature between about 0.degree. C. and about 30.degree. C.;
• where in the above formulae R.sub.1 is an acyl group of the formula ##STR43## wherein R' is (a) C.sub.1 -C.sub.7 alkyl, cyanomethyl, C.sub.1 -C.sub.6 haloalkyl, 4-protected amino-4-protected carboxybutyl;
• or
• (b) C.sub.1 -C.sub.6 alkoxy, phenoxy, benzyloxy or p-methoxybenzyloxy;
• or
• (c) the group --R" wherein R" is phenyl or substituted phenyl wherein the substituents are 1 or 2 halogens, protected hydroxy, cyano, trifluoromethyl, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.4 alkoxy, protected carboxy, protected carboxymethyl, protected hydroxymethyl or protected aminomethyl;
• or
• (d) an arylalkyl group of the formula
• R"--(O).sub.m --CH.sub.2 --
• wherein m is 0 or 2;
• or
• (e) a substituted arylalkyl group of the formula ##STR44## wherein R'" is R" as defined above, 2-thienyl, 3-thienyl, 2-furyl or 3-furyl;
• W is protected hydroxy, protected carboxy, protected amino, or
• (f) a heteroarylmethyl group of the formula
• R""--CH.sub.2 --
• wherein R"" is 2-thienyl, 3-thienyl, 2-furyl, 3-furyl, 2-thiazolyl, 5-tetrazolyl, 1-tetrazolyl;
• R.sub.2 is a carboxy protecting group;
• and R.sub.3 is methyl, ethyl or isopropyl.