On Water: Silver-Catalyzed Domino Approach for the Synthesis of Benzoxazine/Oxazine-Fused Isoquinolines and Naphthyridines from o‑Alkynyl Aldehydes

An operationally simple domino approach for the silver-catalyzed synthesis of oxazine/benzoxazine-fused isoquinolines 5a–q and naphthyridines 6a–v by the reaction of o-alkynyl aldehydes 3a–aa with amines having embedded nucleophiles 4a–d under mild reaction condition in water is described. The reaction shows selective C–N bond formation on the more electrophilic alkynyl carbon resulting in the formation of 6-endo-dig cyclized product. The competitive experiments show the viability of an intramolecular nucleophilic attack over an intermolecular attack of the external nucleophile. This methodology accommodates wide functional group variation, which proves to be useful for structural and biological assessment.