The article presents a novel photocatalytic radical strain-release strategy for the synthesis of azetidines from 1-azabicyclo[1.1.0]butanes (ABBs). The method involves the use of an organic photosensitizer (PS) to promote the homolytic cleavage of sulfonyl imines, generating radical intermediates that react with ABBs to form difunctionalized azetidines in a single step. The PS, characterized by a small energy gap between the first singlet and triplet excited states, efficiently controls the energy transfer process and the formation of the key radical intermediates. The mechanism of the reaction is investigated using spectroscopic and theoretical methods, revealing the role of a transient carbon-centered radical at the azetidine core. The method is demonstrated to be versatile, allowing the synthesis of various azetidine derivatives, including those with biologically relevant scaffolds such as celecoxib and naproxen. The study highlights the potential of this approach in expanding the synthetic repertoire for azetidine-based compounds.The article presents a novel photocatalytic radical strain-release strategy for the synthesis of azetidines from 1-azabicyclo[1.1.0]butanes (ABBs). The method involves the use of an organic photosensitizer (PS) to promote the homolytic cleavage of sulfonyl imines, generating radical intermediates that react with ABBs to form difunctionalized azetidines in a single step. The PS, characterized by a small energy gap between the first singlet and triplet excited states, efficiently controls the energy transfer process and the formation of the key radical intermediates. The mechanism of the reaction is investigated using spectroscopic and theoretical methods, revealing the role of a transient carbon-centered radical at the azetidine core. The method is demonstrated to be versatile, allowing the synthesis of various azetidine derivatives, including those with biologically relevant scaffolds such as celecoxib and naproxen. The study highlights the potential of this approach in expanding the synthetic repertoire for azetidine-based compounds.