Base-Promoted Tandem Cyclization of 2‑(Indol-3-yl)naphthoquinones\nwith Benzamidines toward Polysubstituted Pyrimido[4,5‑<i>b</i>]indoles

A novel and unique approach for the\nconstruction of polysubstituted\npyrimido[4,5-<i>b</i>]indoles from 2-(indol-3-yl)naphthoquinones\nand benzamidines is described. Our strategy, promoted by an inorganic\nbase, involves the ring opening and recyclization of naphthoquinone\nand produces three nitrogen heterocyclic rings via multiple C–N\nbond formations in one pot under transition-metal-free conditions.