The direct assembly of benzo[c]carbazole derivatives via the Diels-Alder reaction of arynes and easily accessible 2-alkenylidoles was reported. By employing different aryne precursor loads, 6,7-dihydrobenzo[c]carbazoles or aryl-substituted 7,11b-dihydrobenzo[c]carbazoles could be controllably generated in good to excellent yields under a nitrogen atmosphere. On the other hand, when the reaction was conducted under oxygen, oxidated/aromatized product benzo[c]carbazoles could be generated directly with high selectivity and efficiency in a one-step manner. Interestingly, the benzo[c]carbazole-5-carboxamide amidation derivatives of the above products showed good antitumor activities. The inhibitory effect of these molecules against cancer cells was also described.