CEPHALOSPORANIC ACID 7-BETA-ALKYLIDENEAMMONIO SALTS

Reaction of 7 beta-aminocephalosporanic acid derivatives 2 with ketone s under acidic conditions leads to the unprecedented formation of alky lideneammonio salts 4. 3'-Halogenated cephalosporanic acid derivatives bearing an unprotected carboxylgroup are normally considered to be se nsitive intermediates that can easily undergo lactonization. However, these compounds are suprisingly stable when transformed into their 7 b eta-alkylideneammonio salts and can thus be elegantly used as versatil e intermediates in cephalosporin chemistry. Copyright (C) 1996 Elsevie r Science Ltd.