Lewis-Acid-Catalyzed Diastereoselective [4 + 2] Cycloaddition of Vinyldiazo Compounds with <i>N</i>-Acyliminium Cations

An FeCl₃-catalyzed [4 + 2] cycloaddition of vinyldiazo compounds with <i>N</i>-acyliminium cations generated from 3-hydroxyisoindolinones is described. A series of diazo-containing isoindolo[2,1-<i>a</i>]quinolinones were constructed in good yields with excellent diastereoselectivities, including those with three contiguous stereogenic centers. The resultant products were readily converted into various isoindolo[2,1-<i>a</i>]quinolinone derivatives based on the rich chemistry of the remaining diazo functionality.