Novel, Chiral, and Enantiopure C 2 ‐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 C 2 ‐symmetrical thioureas that, in combination with 4‐methoxybenzoic acid, promotes the enantioselective protio‐Pictet‐Spengler reaction to provide unprotected tetrahydro‐β‐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.