A base-regulated one-pot protocol for the tunable synthesis of pyridobenzoxazepinones and pyridobenzoxazines has been developed. The preparation of pyridobenzoxazepinones is achieved in moderate to good yield by utilizing an aromatic nucleophilic substitution (S_NAr, O-arylation)/carbonylation tandem reaction. Mechanistic studies suggest that S_NAr (O-arylation) proceeds prior to the aminocarbonylation. Through the regulation of bases, pyridobenzoxazines can be obtained via successive S_NAr (O-arylation and then N-arylation). Base is crucial for the regulation of the products.