A chemical reductant or a sacrificial electron donor is required in any reduction reactions, generally resulting in undesired chemical waste. Herein, we report a reductant-free reductive [3 + 2 + 1] annulation of β-keto amides with CS2 enabled by the synergy of electro/copper/base using water as an innocuous anodic sacrifice with O2 as a sustainable by-product. This electrochemical protocol is mild and provides access to polyfunctionalized pyridin-2-ones from simple starting materials in a single step.