1,4-Dibenzodiazepines, an important component of nitrogen-containing heterocycles, are widely present in drugs. Herein, we developed a photochemical radical cascade cyclization reaction of isocyanides with α-carbonyl bromides under mild conditions. A sequence of 11-alkyl-substituted 1,4-dibenzodiazepines were produced in 53%-85% yields, demonstrating excellent tolerance towards various functional groups. Primary, secondary, and tertiary α-carbonyl bromides were effectively employed as alkyl reagents.