Heteroatom substituent, cephalosporin

Not until 1970 were research efforts directed toward the preparation and testing of cephalosporins with an electronegative heteroatom substituent directly attached to the C-3 position of the cephem ring system. This variation of the molecule became a feasible goal when both chemical and electrochemical methods were developed independently in several laboratories that produce 3-methylenecephams in practical quantities. 

This section aims to complete the picture on the studies summarized in CHEC-II(1996) on the synthesis of classical cephalosporins, describing the main cephalosporin methodologies developed during the last decade. In CHEC-II(1996), an approach was presented for the formation of the cephalosporin framework bearing various heteroatom and carbon substituents at the C-3 position, which relies on a sequential addition/cyclization of allenoate 70, derived from penicillin G. 

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