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

A catalytic intramolecular aza‐Wittig reaction of azide‐functionalized imides has been developed under PIII/PV 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 PIII/PV redox organocatalysis and provides a practical and sustainable catalytic alternative to classical stoichiometric phosphine‐mediated aza‐Wittig reactions.