The addition reactions between aromatic azoarenes and N-substituted formamides are described. This direct and practical method provides a novel approach for the synthesis of formylhydrazines and semicarbazides in the presence of NaI/DTBP and imidazole/DCP catalytic systems, respectively. It can be seen that C–H or C–N from N-substituted formamides could be cleaved selectively under such transition-metal-free conditions. This is the first successful example of direct addition of N-substituted formamides to N=N bond.