Process for the preparation of azetidines

A process of preparing azetidines of the formula ##STR22## wherein R.sub.1 is a conventional penicillin- or cephalosporinacylamido group, R.sub.2 represents one of the groups of the following formulae:

• ##STR23## wherein R.sub.4, R.sub.5 and R.sub.6 are individually selected from the group consisting of hydrogen, lower alkyl and lower alkenyl, n is 2 or 3 and--in case formula IIB represents a phenylene group--this group may carry one to four further substituents selected from the group consisting of halogen, lower alkyl, lower alkenyl and phenyl, R.sub.3 is an amino group of the formula ##STR24## wherein R.sub.7 is hydrogen or lower alkyl and R.sub.8 is lower alkyl. or R.sub.3 is a N,N'-disubstituted hydrazino group wherein the substituents are lower alkyl groups, or R.sub.3 is --OR.sub.9 wherein R.sub.9 is hydrogen, lower alkyl or lower alkyl substituted by 1 to 3 halogen atoms or by 1 or 2 phenyl groups, wherein the phenyl groups may be substituted by a methoxy or a nitro group, or R.sub.9 represents the phenacyl group or a salt-forming cation selected from the group consisting of alkali metal and alkaline earth metal ions, and corresponding azetidines of formula I wherein the double bond in the propenyl side chain has been shifted from the 2-to the 1-position which comprises the step of reacting a penicillanic sulfoxide of the formulae ##STR25## wherein R.sub.1 is as defined above and R.sub.3 ' has the same significance as defined for symbol R.sub.3 except that when R.sub.3 ' represents --OR.sub.9, R.sub.9 does not represent a salt-forming cation, but R.sub.9 also represents a silyl group of one of the following formulae:
• ##STR26## wherein the symbols R.sub.10 are the same or different and each represents a lower alkyl or alkoxy group or lower alkyl or lower alkoxy substituted by a halogen atom, or a phenyl group, X is a halogen atom and R.sub.11 is a penicillanic sulfoxide acyl group of the formulae:
• ##STR27## wherein R.sub.1 is as defined above with a silicon-containing compound of the formula ##STR28## wherein R.sub.2 and R.sub.10 are as hereinbefore defined, under anhydrous conditions, in an inert organic solvent at temperature between 50.degree. and 180.degree. C.