4(Formylthio)-azetidin-2-ones and ozonization process therefor

A compound of the formula ##STR12## wherein:

• R.sub.1 is a readily removable carboxylic acid protecting group which is substantially unreactive toward ozone;
• and
• R.sub.2 is phthalamido or a group having the formula ##STR13## wherein:
• R.sub.3 is
• 1. hydrogen, C.sub.1 -C.sub.3 alkyl, halomethyl, benzyloxy, 4-nitrobenzyloxy, tert.-butyloxy, 2,2,2-trichloroethoxy, 4-methoxybenzyloxy, 4-protected amino-4-protected carboxybutyl in which the amino protecting group and carboxy protecting group are substantially unreactive toward ozone;
• or
• 2. a group of the formula
• R.sub.4 --(O).sub.m --CH.sub.2 --
• wherein:
• m is 0 or 1;
• and
• R.sub.4 is phenyl or phenyl substituted with 1 or 2 halogens, nitro, cyano, trifluoromethyl, C.sub.1 -C.sub.4 alkyl, C.sub.1 -C.sub.2 alkoxy, protected hydroxy in which the hydroxy protecting group is substantially unreactive toward ozone;
• or
• 3. a group of the formula ##STR14## wherein:
• R.sub.4 is as defined above and
• W is protected hydroxy, protected carboxy, or protected amino in which the hydroxy protecting group, the carboxy protecting group and the amino protecting group are substantially unreactive toward ozone.