P ^III /P ^V Redox Organocatalysis Enables Intramolecular Aza‐Wittig Cyclizations of Imides: Direct Access to Pharmaceutically Relevant Amidine Scaffo

A catalytic intramolecular aza‐Wittig reaction of azide‐functionalized imides has been developed under P ^III /P ^V redox organocatalytic conditions, enabling rapid and direct access to structurally diverse amidine‐containing heterocycles. The transformation is promoted by a methanophosphocine oxide catalyst in combination with phenylsilane as the reductant and bis(4‐nitrophenyl) phosphate (BNPA) as a Brønsted acid additive. Under mild, metal‐free conditions (2 mol% catalyst, 5 mol% additive), a broad spectrum of imides undergoes efficient cyclization to furnish fused nitrogen heterocycles in yields up to 96%. The method displays broad functional‐group tolerance, including halogenated, alkyl‐substituted, and structurally complex substrates, such as thalidomide derivatives, and enables access to a wide range of privileged amidine scaffolds. Its synthetic utility is further highlighted through concise applications to quinazolinone precursor synthesis and the antitumor agent batracylin. This work expands the scope of P ^III /P ^V redox organocatalysis and provides a practical and sustainable catalytic alternative to classical stoichiometric phosphine‐mediated aza‐Wittig reactions.