Enantioselective Pictet−Spengler-Type Cyclizations of Hydroxylactams: H-Bond Donor Catalysis by Anion Binding

Highly enantioenriched indolizinone and quinolizinone products are obtained in the thiourea-catalyzed cyclization of tryptamine-derived hydroxylactams. Substituent and counterion effect studies point to a novel mechanism of catalysis involving rate-limiting anion abstraction and binding by the thiourea.