Novel, Chiral, and Enantiopure C2‐Symmetric Thioureas Promote Asymmetric Protio‐Pictet‐Spengler Reactions by Anion‐Binding Catalysis

Although anion-binding processes are well-known for their crucial role in molecular recognition, they have only recently been utilized for catalysis. Herein, a new class of chiral,enantiopure C2-symmetrical thioureas that, in combination with 4-methoxybenzoic acid, promotes the enantioselective protio- Pictet-Spengler reaction to provide unprotected tetrahydro-carbolines in good yields (40–93 %) and moderate-to-high enantioselectivities (34–95% ee) in one step from tryptamine and aldehyde derivatives is described. The formation of a chiral catalyst-anion complex was explored by 1 H NMR.