"On Water" Catalytic Aldol Reaction Between Isatins and Acetophenones: Interfacial Hydrogen Bonding and Enamine Mechanism

"On water" catalytic aldol reaction catalyzed by polyetheramine (D230) has been developed for easy access to 3-substituted 3-hydroxyindolin-2-ones through the reaction between various substituted isatins and acetophenones/cyclic ketones in high yields under room temperature. Systematic mechanism investigation uncovers the secret for the on water catalytic aldol reaction: comparison of the heterogeneous and homogeneous reaction circumstances with yields of 95 and 20%, respectively, indicates the on-water reaction dominating; interfacial hydrogen bonding between isatin with HO is tested based on the downfield shift of the C2 and C3's C NMR signals when water was added to the CDCl solution of isatin; Lewis base polyetheramine D230 catalyzes the aldol reaction via the enamine mechanism verified by in situ NMR and ESI-MS analysis.