Abstract: | ‘7-aminocephalocillanic acid’ 1 , an intermediate for the preparation of new β-lactam antibiotics was prepared by transforming the β-lactam carbinol 2a to the phosphorane 9a through several steps. Oxydation of 9a with DMSO/Ac2O led directly to the cyclized ester 11a , which has been converted into 1 by known methods. |