Proline-Catalyzed Asymmetric Formal α-Alkylation of Aldehydes via Vinylogous Iminium Ion Intermediates Generated from Arylsulfonyl Indoles


  • D. Agostino is gratefully acknowledged for his help. This work was supported by Bologna University and by MIUR National Project “Stereoselezione in Sintesi Organica”.


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Proline strikes again: The intermolecular enamine-catalyzed asymmetric “formal” α-alkylation of aldehydes is described. Alkylating reagent 1 generates a highly stabilized carbocation, which can readily intercept the enamine intermediate. L-Proline proved to be the best catalyst, providing an easy route to relevant 3-indolyl derivatives 2 with high diastereo- and enantiocontrol.