The Enantioselective Organocatalytic 1,4-Addition of Electron-Rich Benzenes to α,β-Unsaturated Aldehydes

The first enantioselective organocatalytic alkylation of electron-rich benzene rings with alpha,beta-unsaturated aldehydes has been accomplished. The use of iminium catalysis has provided a new strategy for the enantioselective construction of benzylic stereogenicity, an important chiral synthon for natural product and medicinal agent synthesis. The (2S,5S)-5-benzyl-2-tert-butylimidazolidinone amine catalyst has been found to mediate the conjugate addition of a wide variety of substituted and unsubstituted anilines to unsaturated aldehydes. A diverse spectrum of aldehyde substrates can also be accommodated in this new organocatalytic transformation. While catalyst quantities of 10 mol % were generally employed in this study, successful alkylations conducted with catalyst loadings as low as 1 mol % are described.