AZETIDINON ETTIKSYRADERIVAT OCH FORFARANDE FOR FRAMSTELLNING DERAV

New compounds of the general formula (I), wherein Y and Y form together a removable carbonyl protecting group and X is a selectively removable esterifying group, are prepared in the way that a compound of the general formula (IV), wherein Y and Y are as defined above, is nitrated and then reduced, the resulting new compound of the general formula (III), wherein Y and Y are as defined above and A stands for nitro group and then for amino group, is converted into a new ester of the general formula (II), wherein Y , Y and X are as defined above, in a manner known per se, and the aminophenyl protecting group of the resulting compound is split off. The new compounds of the general formula (I) can be applied primarily as intermediates in the synthesis of thienamycin or thienamycin analogues.