Palladium(II)-Catalyzed Direct Access to Indeno[1,2-c]isochromen-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 alpha,beta-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.