A metal-free N-iodosuccinimde (NIS)/2,2,6,6-tetramethylpiperidinyloxy (TEMPO)-promoted protocol was developed for the oxidative α-cyanation and nitro-Mannich reaction of tertiary amines via a cross-dehydrogenative coupling reaction under mild conditions. Several control experiments were performed; the coupling reaction outcomes indicated that the C-N coupled intermediate (N-Mannich base) formed from the tertiary amine and NIS had a stabilizing effect on the iminium cation.