Chiral Lewis Acid-Mediated Enantioselective Pictet-Spengler Reaction of N(b)-Hydroxytryptamine with Aldehydes.

The first example of a reagent-controlled enantioselective Pictet-Spengler reaction is demonstrated. Using diisopinocampheylchloroborane as a chiral Lewis acid catalyst, the Pictet-Spengler reaction of N(b)-hydroxytryptamine with aldehydes gave the corresponding 2-hydroxytetrahydro-beta-carbolines in up to 90% ee. The enantioselective Pictet-Spengler reaction catalyzed by chiral binaphthol-derived Brønsted acid-assisted Lewis acids, with up to 91% ee, is also demonstrated.