Sc(OTf) 3 -Catalyzed (3 + 3) Annulation of Quinoxaline-2(1 H )-thiones and Donor–Acceptor Cyclopropanes

The Sc(OTf)3-catalyzed (3 + 3) annulation of quinoxaline-2(1H)-thiones and donor–acceptor cyclopropanes was achieved in the presence of DBU under air to give functionalized 2,3-dihydro-4H-thiopyrano[2,3-b]quinoxaline derivatives in moderate to high yields. The annulation includes tandem nucleophilic ring opening, nucleophilic addition, and radical oxidative aromatization. It provides not only a new (3 + 3) annulation strategy but also a new synthetic method for fused tricyclic quinoxaline derivatives.