Abstract: An improved method for the preparation of 2-chloro sulfinyl azetidin-4-one of the formula: ##STR1## wherein R is: hydrogen; C.sub.1 -C.sub.3 alkyl; halomethyl; cyanomethyl; phenyl; substituted phenyl; phenoxy, benzyloxy- or substituted benzyl; a group of the formula R.sub.2 --O--wherein R.sub.2 is t-butyl, 2,2,2-trichloroethyl, benzyl or substituted benzyl; a group of the formula R.sub.3 --(O).sub.n --CH.sub.2 wherein R.sub.3 is phenyl or substituted phenyl. The 2-chlorosulfinylazetidin-4-one is prepared by reacting a penicillin sulfoxide ester of the general formula ##STR2## wherein R and R.sub.1 have the meanings defined above with an N-chloro halogenating agent in an inert organic solvent. The reaction is carried out in the presence of an acid scavenging amount of a phosphate or hydrogen phosphate of an alkali metal, alkaline earth metal, ammonium, quaternary ammonium or mixtures thereof.

Abstract: A process for the manufacture of 3-exomethylene cepham sulfoxide ester of the formula ##STR1## wherein R is hydrogen, C.sub.1 -C.sub.3 alkyl, halomethyl, phenyl, substituted phenyl cyanomethyl, phenoxy, benzyloxy or substituted benzyl with a substituent group such as that selected from halo, alkyl, alkoxy, protected hydroxy, nitro, cyano and trifiuoromethyl, a group of the formula R.sub.2 --0-- wherein R.sub.2 is t-butyl, 2,2,2-trichloro ethyl, benzyl or substituted benzyl; a group of the formula R.sub.3 --[0].sub.n --CH.sub.2, wherein R.sub.3 is phenyl or substituted phenyl with the substituent group selected from halo, alkyl, alkoxy, protected hydroxy, nitro, cyano, or 1,4-cyclohexadienyl, and n is 0 or 1; or a substituted arylalkyl group of formula R.sub.4 --CH where R.sub.4 has the same meaning as R.sub.3 defined above and W is a protected hydroxy or protected amino group; and R.sub.1 is a carboxylic acid protecting group such as that selected from the group consisting of C.sub.1 -C.sub.