Visible‐light mediated Ugi‐type reaction for the synthesis of 3,3‐disubstituted phthalides

Abstract The synthesis of diverse phthalides containing quaternary carbon centers remains poorly exploited, requiring stepwise reactions with toxic reagents under high temperatures. Herein, we describe a visible‐light promoted, photo‐ and metal‐catalyst‐free protocol for the modular synthesis of 3,3‐disubstituted phthalides with water as the sole by‐product. This process featured an open‐flask operation of a three‐component reaction involving an isocoumarin as the self‐photosensitizer for aerobic ring contracting rearrangements, allowing the convenient preparation of 3‐(1′‐indolyl)‐phthalides in moderate to good yields. The mechanistic investigations suggested that singlet oxygen ( 1 O 2 ) was generated through an energy‐transfer pathway.