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Regiodivergent Intramolecular Nucleophilic Addition of Ketimines for the Diverse Synthesis of Azacycles.

Azacycles such as indoles and tetrahydroquinolines are privileged structures in drug development. Efficient strategies for the diverse synthesis of azacycles are highly sought after. Here, we report on an unprecedented regiodivergent intramolecular nucleophilic addition reaction of imines as a flexible approach to access N-functionalized indoles or tetrahydroquinolines, by the control of reaction at the N-terminus or C-terminus. Using ketimines derived from 2-(2-nitroethyl)anilines with isatins or α-ketoesters, the regioselective N-attack reaction gives N-functionalized indoles, while the catalytic enantioselective C-attack reaction affords chiral tetrahydroquinolines featuring an α-tetrasubstituted stereocenter. Mechanistic studies reveal that H-bonding interactions may greatly facilitate such unusual N-attack reactions of imines. The utility of this protocol is highlighted by the catalytic enantioselective formal synthesis of (-)-psychotrimine, and the construction of various fused aza-heterocycles, using the resulting N-functionalized indoles that are otherwise difficult to access using other synthetic methods.