Enantioselective β-Functionalization of Aldehydes via Oxidative Enamine Catalysis

Significance

The authors expand enamine-­iminium catalysis for the β-functionalization of aldehydes via enamine oxidation. By using a stoichiometric amount of an oxidant (e.g., IBX), in situ generated enamines are oxidized to the corresponding α,β-unsaturated iminium ions, which ­undergo Michael reactions with moderate yields and good to excellent enantioselectivities. The synthetic potential of this methodology is also demonstrated by conducting various cascade ­reactions, which give rise to complex chiral building blocks from simple aldehydes. In the absence of a nucleophile, the authors could observe the corresponding α,β-unsaturated enal, which is formed via hydrolysis of the iminium intermediate.