To sum up, we have developed the FeCl3 or Sc(OTf)3 to catalyze intermolecular formal [8+3] cycloaddition of azaheptafulvenes with BCBs involving two-electron reaction process promoted by Lewis acid to provide a direct construction of polycyclic compounds under mild conditions. It is noteworthy that this atom-economical reaction is tolerant of a broad range of azaheptafulvenes with BCBs. Moreover, the amplification experiments and synthetic transformations of the cycloaddition compounds highlighted its practicality. Further research on the development of new strategies for intermolecular formal [8+3] reactions of bicyclo [1.1.0]butanes (BCBs) catalyzed by Lewis acids is currently underway in our laboratory.