Abstract Electrolysis of 3-arylthiomethyl-Δ ³-cephems possessing various substituents on the arylthio moiety undergo chemoselective and product-selective electrooxidation to give several different products. These include isomeric mixtures of the corresponding methoxylated cephems, a bis [(Δ ³-cephem-3-yl) methyl] disulfide or a 3-dimethoxymethyl-Δ ³- cephem. The selectivity of the oxidation is highly dependent on the nature of the ...