Enantioselective Gold-Catalyzed Pictet–Spengler Reaction

Cationic chiral Au­(I) complexes catalyze asymmetric Pictet–Spengler reactions between tryptamines and arylaldehydes. The resulting tetrahydro-β-carbolines are obtained with wide functional group tolerance in high yield and with high enantioselectivities (up to 95%). Aldehydes bearing polar or protic functions are well tolerated. The reaction features a hitherto unknown C2-auration of the indole as the key step, supported by density functional theory calculations.