A base-mediated aerobic oxidation of the C-H bond adjacent to the N-atom of a secondary amine to form an imine intermediate under mild metal-free basic conditions has been developed. Accordingly, this new strategy has been successfully applied to the synthesis of various di-, tri-, and tetra-substituted α-aminocyclopentenones through a tandem aerobic oxidative [4 + 1] carbocyclization reaction of N-aryl α'-amino-α,β-unsaturated ketones as C4 1,4-dielectrophiles with active methylenes, including ethyl isocyanoacetate, nitroalkanes, and ethyl cyanoacetate, as C1 components.