A photocatalyst‐free cascade reaction of N‐alkyl‐N‐arylmethacrylamides with monoalkyl cesium oxalate salts is described. In the presence of visible light and (NH4)2S2O8, monoalkyl cesium oxalate salts undergo single‐electron oxidation/CO2 extrusion to generate alkyl radicals, followed by the addition and subsequent cyclization to give alkylated oxindoles. In addition, N‐alkyl‐N‐methacryloylbenzamides could be applied for the cascade reaction, providing a series of alkylated isoquinolinediones, which are completely different from the products obtained with monoalkyl oxalates as substrates.