Organocatalytic enantioselective aza-Friedel-Crafts reactions of cyclic ketimines with pyrroles or indoles were catalyzed by imidazoline/phosphoric acid catalysts. The reaction was applied to various 3H-indol-3-ones to afford products in excellent yields and enantioselectivities. The chiral catalysts can be recovered by a single separation step using column chromatography and are reusable without further purification. Based on the experimental investigations, a possible transition state has been proposed to explain the origin of the asymmetric induction.
Chiral Phosphoric Acid Catalysts Organocatalytic enantioselective aza‐Friedel–Crafts reactions of cyclic ketimines with pyrroles or indole were catalyzed by imidazolinephosphoric acid catalysts. The reaction was applied to various 3H‐indol‐3‐ones to afford products in excellent yields and enantioselectivities. The graphics shows origami cranes that fly with expanded wings. The bis(imidazoline)/phosphoric acid catalysts also expand their wings like the origami cranes, and form a well‐fitting asymmetric space for substrate binding to let the reaction “fly”. The full story can be found in the Communication by S. Nakamura and colleagues on page 9478 ff.
The title reaction between 2‐phenyl‐3H‐indol‐3‐one and various pyrrole, indole and tryptamine derivatives proceeds with excellent yields and enantioselectivities.
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