Visible‐Light Promoted Intramolecular para‐Cycloadditions on Simple Aromatics

Dearomative cycloadditions are a powerful tool to access a large chemical space exploiting simple and ubiquitous building blocks. The energetic burden due to the loss of aromaticity has however greatly limited their synthetic potential. We devised a general intramolecular method that overcomes these limitations thanks to the photosensitization of allenamides. The visible‐light‐promoted process gives complex [2.2.2]‐(hetero)‐bicyclooctadienes at room temperature, likely through the stabilization of transient (bi)radicals by naphthalene. The reaction tolerates several valuable functionalities, offering a convenient handle for a myriad of applications, including original isoindoles and metal complexes. We present the first synthesis of bridged bicycles through the dearomatization of sterically and electronically unbiased aryl fragments. The visible‐light promoted method occurs at room temperature and has ample functional‐group tolerance. The key to the difunctionalization of the aryl partner is the use of naphthalene as an additive, which stabilizes transient (bi)radicals through its extended π cloud. This effect might lead to its broad use in radical sequences.