Synthesis of Spiro[benzo[ d ][1,3]oxazine-4,4'-isoquinoline]s via [4+1+1] Annulation of N -Aryl Amidines with Diazo Homophthalimides and O 2 .

Synthesis of spiro[benzo[ d ][1,3]oxazine-4,4'-isoquinoline]s through a unique [4+1+1] annulation of N -aryl amidines with diazo homophthalimides and O 2 is presented. This unprecedented spirocyclization reaction features readily obtainable substrates, structurally and pharmaceutically attractive products, a cost-free and clean oxygen source, sustainable reaction medium, tolerance of a broad spectrum of functional groups, and an interesting reaction mechanism based on sequential C(sp 2 )-H/C(sp 3 )-H bond cleavage and oxygen insertion.