electrolysis setup gives rise to divergent siteselectivity: a divided electrochemical cell leads to C5-carboxylation, whereas an undivided cell promotes C4-carboxylation. The undivided cell reaction is proposed to operate via a paired electrolysis mechanism9,10, wherein both cathodic and anodic events play critical roles in altering the siteselectivity. Specifically, anodically-generated iodine preferentially