Asymmetric Iminium Ion Catalysis with a Novel Bifunctional Primary Amine Thiourea: Controlling Adjacent Quaternary and Tertiary Stereocenters

The development of a new bifunctional chiral primary amine thiourea catalyst and its application in the first asymmetric conjugate addition of oxindoles to enales was described. The reaction between 3-methyl oxindole and cinnamaldehyde, a combination of simple and readily available starting materials that targets in organic synthesis, was selected. The poor catalytic performance and the very low selectivity observed suggest a critical role of the thiourea moiety during the steroselective C-C bond-forming step. It is also found that by using 50% of benzoic acid, the catalyst loading is reduced to 10%, while still maintaining high diastero and enantiocontrol, and significant reactivity. The best diasterocontrol is observed for enals that have a naphthyl β substituted and by using oxindole that has a benzyl substitute.