Cyclopropylamine-Derived Distonic Iminium Radicals: Photoinduced Strategies in Chemo- and Stereo-Selective Synthesis

Cyclopropylamines have emerged as privileged substrates in photocatalysis owing to their propensity to undergo single‑electron oxidation followed by strain‑release β-scission, generating highly reactive distonic iminium radicals. These intermediates underpin a broad repertoire of light-driven transformations, including ring‑opening functionalization, formal [3 + 2] cycloadditions, radical cascade processes, and asymmetric bond-forming reactions. This Review highlights recent advances in the photochemical activation of cyclopropylamines, emphasizing mechanistic insights, catalyst design, and the synthetic potential of these reactions for accessing complex carbocycles, heterocycles, and medicinally relevant scaffolds. This review is organized to first summarize the preparation of cyclopropylamine derivatives, then to discuss their photoinduced rearrangements and ring‑opening pathways, followed by an overview of [3 + 2] cycloadditions, enantioselective strategies, and applications for constructing unconventional building blocks. Together, these developments underscore the growing impact of cyclopropylamine-derived radicals as versatile tools in modern synthetic methodology.