Asymmetric Aziridination of Allylic Carbamates using Ion-Paired Rhodium Complexes and Extrapolation to C-H Amination of Phenethyl Carbamates.

Abstract

Aziridination of alkenes is an important route to chiral nitrogen-containing building blocks. Here we report that carbamate-functionalized allylic alcohols undergo highly enantioselective aziridination using achiral dimeric Rh(II,II) complexes that are ion-paired with cinchona alkaloid-derived chiral cations. The aziridine-containing products are amenable to a variety of further reactions to generate useful groupings of functionality. Furthermore, we show that the carbamate group is effective for directing highly enantioselective benzylic C-H amination when it is appended to phenethyl alcohols. Intermolecular C-H amination of phenethyl alcohol derivatives has proven highly challenging to achieve asymmetrically yet gives rise to valuable β-amino alcohols. Both processes result in rapid access to versatile, highly enantioenriched small molecule building blocks for synthesis and highlight the effectiveness and generality of this chiral cation-based strategy for asymmetric catalysis. We report studies that probe important structural features of the chiral cation and demonstrate that the ion-paired complexes can be formed from their individual components without a separate isolation step.