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 1 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-hydrozyindole derivative via a synthetically useful indoline intermediate.