Hypervalent-iodine-mediated cascade annulation of diarylalkynes forming spiro heterocycles under metal-free conditions.

An unusual reaction featuring the cascade annulation of internal alkynes to afford spiro heterocycles as the products has been realized for the first time with a hypervalent iodine reagent as the only oxidant. This unprecedented process encompasses not only two sequential C-N/C-O-bond formations, but also the insertion of a carbonyl oxygen, all in one pot under metal-free conditions.