Highly Enantioselective\nSynthesis of Polycyclic Dihydroisoquinolinones\nvia NHC-Catalyzed [4 + 2] Annulations

The NHC-catalyzed enantioselective [4 + 2] annulation\nof 9<i>H</i>-fluorene-1-carbaldenydes with cyclic imines\nwas successfully\ndeveloped. A series of optically enriched polycyclic dihydroisoquinolinones\nwere synthesized in moderate to excellent yields with good to excellent\nenantioselectivities. In addition, this efficient method could also\nbe amenable to the synthesis of spirocyclic compounds by using isatin-derived\nketimines as the electrophiles.