Synthesis of chromeno[4,3,2-cd]isoindolin-2-ones and chromeno[4,3,2-de]isoquinolin-3-ones. Electrophilic versus anionic cyclization of carbamates

The total synthesis of chromeno[4,3,2-cd]isoindolin-2-ones 6a-d and chromeno[4,3,2-de]isoquinolin-3-ones 15a-b from 4-methoxy-9H-xanthen-9-one is reported. The construction of the nitrogenated ring was attempted by both intramolecular electrophilic and anionic cyclizations of the corresponding carbamate precursors. Only anionic cyclization was possible for isoindolinones, but for isoquinolinones the electrophilic and anionic routes both afforded excellent yields.