Base-Promoted Tandem Cyclization of 2-(Indol-3-yl)naphthoquinones with Benzamidines toward Polysubstituted Pyrimido[4,5-b]indoles

]indoles from 2-(indol-3-yl)naphthoquinones and benzamidines is described. Our strategy, promoted by an inorganic base, involves the ring opening and recyclization of naphthoquinone and produces three nitrogen heterocyclic rings via multiple C-N bond formations in one pot under transition-metal-free conditions.