Electrochemical reduction of cephalosporanic acids

Electrochemical reduction of cephalosporanic acid derivatives (I) bearing various substituents at the 3-position gave the corresponding 3-methylenecepham derivatives (II), a new class of cephalosporins. Reductive opening of the 3-hydroxymethyl-3-cephem-4-carboxylic acid lactone (IV) was effected to give (II) by cathodic reaction. The 3-methylenecepham derivatives (II) were readily isomerized to the 3-methyl-3-cephem derivatives (III) providing a new synthesis of cephalexin [7-(D-2-amino-2-phenylacetamido)-3-methyl-3-cephem-4-carboxylic acid](IIIc). The reaction mechanism is discussed on the basis of deuteriation and polarography of the cephalosporins involved.