A photocatalytic radical strategy has been developed for the synthesis of densely functionalized azetidines from azabicyclo[1.1.0]butanes (ABBs). The method utilizes an organic photosensitizer to control the energy transfer process with sulfonyl imines, generating radical intermediates that react with ABBs via a strain-release mechanism to produce difunctionalized azetidines in a single step. This approach is supported by spectroscopic, optical, and density functional theory (DFT) studies. The strategy offers broad applicability, demonstrated by the synthesis of various azetidine derivatives, including those of celecoxib and naproxen. The method involves the homolytic cleavage of sulfonyl imine precursors, leading to the formation of sulfonyl and iminyl radicals that react with ABBs. Mechanistic studies reveal that the reaction proceeds via a radical strain-release pathway, with the key intermediate being a carbon-centered radical that facilitates the insertion of nitrogen, sulfur, and hydrogen. The process is efficient, selective, and compatible with a wide range of substrates, including various sulfonyl imines and ABB precursors. The method also enables the synthesis of diverse azetidine scaffolds, including those with biologically relevant structures. The approach represents a significant advancement in the synthesis of azetidines, offering a new pathway for their functionalization and expanding the synthetic repertoire for their construction. The study highlights the potential of radical strain-release photocatalysis in the development of new organic and medicinal chemistry methods.A photocatalytic radical strategy has been developed for the synthesis of densely functionalized azetidines from azabicyclo[1.1.0]butanes (ABBs). The method utilizes an organic photosensitizer to control the energy transfer process with sulfonyl imines, generating radical intermediates that react with ABBs via a strain-release mechanism to produce difunctionalized azetidines in a single step. This approach is supported by spectroscopic, optical, and density functional theory (DFT) studies. The strategy offers broad applicability, demonstrated by the synthesis of various azetidine derivatives, including those of celecoxib and naproxen. The method involves the homolytic cleavage of sulfonyl imine precursors, leading to the formation of sulfonyl and iminyl radicals that react with ABBs. Mechanistic studies reveal that the reaction proceeds via a radical strain-release pathway, with the key intermediate being a carbon-centered radical that facilitates the insertion of nitrogen, sulfur, and hydrogen. The process is efficient, selective, and compatible with a wide range of substrates, including various sulfonyl imines and ABB precursors. The method also enables the synthesis of diverse azetidine scaffolds, including those with biologically relevant structures. The approach represents a significant advancement in the synthesis of azetidines, offering a new pathway for their functionalization and expanding the synthetic repertoire for their construction. The study highlights the potential of radical strain-release photocatalysis in the development of new organic and medicinal chemistry methods.