Visible‐Light‐Promoted, (Photo)catalyst‐Free Synthesis of 3‐Sulfonyl‐Azaspiro[4.5]trienones via Arylazo Sulfones

Here, 3‐sulfonyl‐azaspiro[4.5]trienones are now accessible via a versatile visible‐light‐driven dearomative strategy under metal‐ and (photo)catalyst‐free conditions, starting from differently substituted N ‐aryl propiolamides and arylazo sulfones. The protocol employs ethyl acetate as a benign solvent and tert‐butyl hydroperoxide as the oxidant. The reaction proceeds through direct photoexcitation of the arylazo sulfone, which acts simultaneously as a light absorber and a sulfonyl‐radical source, enabling ipso‐spirocyclization of aromatic amides. This transformation combines a broad substrate scope with mild conditions and operational simplicity, providing a valuable synthetic entry to sulfur‐containing spiroheterocycles of pharmacological interest.