Syntheses of 2‑Iminoindolin-3-ones and 2‑Alknyl-2,3-dihydroquinazolin-4(1H)‑ones from 3‑Diazoindolin-2-imines

3-Diazoindolin-2-imines reacted with nitrones to furnish 2-iminoindolin-3-ones through a Au­(I)-catalyzed cascade oxygen transfer/imine exchange process. The prepared 2-iminoindolin-3-ones could be further transformed into 2-alknyl-2,3-dihydroquinazolin-4­(1H)-ones through a Ag­(I)-catalyzed reaction with terminal alkynes. A MeOH-triggered ring expansion mechanism involving cyclic iminium formation and nucleophilic addition is proposed for this novel alkynylation reaction. This two-step procedure provides a general and convenient approach to 2-alknyl-2,3-dihydroquinazolin-4­(1H)-ones, which are privileged structures in medicinal chemistry.