Amide-assisted intramolecular [3+2] annulation of cyclopropane ring-opening: a facile and diastereoselective access to the tricyclic core of (±)-scandine.

The highly diastereoselective intramolecular [3+2] annulation via the ring-opening of a cyclopropane diester derivative has been developed to construct a dihydroquinolinone scaffold. A series of tricyclic dihydroquinolinones bearing one or two all-carbon quaternary stereogenic centers were obtained in good yields and excellent diastereoselectivities (up to 20 : 1 dr). Moreover, the amide-linking mode shows obviously beneficial effects on the ring-opening of cyclopropane.