Lighting the Path to Cyclic Phosphonamides via Halogen‐Bond Electron Donor–Acceptor Activation

Phosphinamide‐based scaffolds and related P ‐heterocycles emerge as valuable scaffolds in optoelectronics, particularly OLED technologies, as well as in asymmetric catalysis. However, access to cyclic phosphinamides remains synthetically challenging and poorly described, limiting exploration of their full potential. We report here an efficient, mild, metal‐free, and photocatalyst‐free photoinduced strategy that expands the synthetic toolbox to reach cyclic phosphinamides and thiophosphinamides. This approach relies on halogen‐bond‐assisted electron donor–acceptor (HBA‐EDA) complex formation to trigger single‐electron transfer and promote efficient CC bond construction under gentle conditions. Comprehensive mechanistic studies, including UV, radical quenching, EPR (electron paramagnetic resonance), and DFT (Density functional theory) analyses, confirm the involvement of carbon‐ and phosphorus‐centered radicals and elucidate key intermediates, including a rearrangement process that defines two operative mechanistic pathways. This method provides a straightforward and sustainable way to access new phosphorus‐containing compounds with potential for future optoelectronic applications, as well as new insights into HBA‐EDA mechanism.