Palladium(II)‐Catalyzed Direct Access to Indenoisochromen‐5(11H)‐Ones via Intramolecular Oxypalladation‐Initiated Cascade Process

A palladium(II)‐catalyzed cascade approach was established for the synthesis of indeno[1,2‐c]isochromen‐5(11H)‐ones starting from 2‐alkynyl tert‐butyl benzoates bearing a pendant α,β‐unsaturated carbonyl moiety in high yields (up to 99%) under mild conditions. This strategy offered high atom and step economy by delivering isobutene as the only side product, and by generating two new bonds and two rings in a single synthetic operation. The mechanism of the cascade process was visualized comprising sequential intramolecular oxypalladation (6‐endo‐dig), intramolecular olefin insertion, and protonation steps.