Ring-opening cyclization of cyclohexane-1,3-dione-2-spirocyclopropanes with amines: Rapid access to 2-substituted 4-hydroxyindole

An efficient ring-opening cyclization of cyclohexane-1,3-dione-2- spirocyclopropanes with primary amines has been developed. The reaction proceeded at room temperature without any additives to provide 2-substituted tetrahydroindol-4-ones in good to excellent yields without the formation of the 3-substituted isomers. The obtained product was readily converted into a 2-substituted 4-hydroxyindole derivative via a synthetically useful indoline intermediate.