Enantioselective radical addition reactions to imines using binaphthol-derived chiral N-triflyl phosphoramides
作者:Sunggi Lee、Sunggak Kim
DOI:10.1016/j.tetlet.2009.02.136
日期:2009.7
Binaphthol-derived chiral phosphoric acid catalysts were applied to enantioselective radical addition reactions of imines and provided chiral amines with good enantioselectivities (73–84% ee). Furthermore, the enantioselectivities were not affected by either electronic properties of phenyl imines or radical precursors.
Schiff bases Ar1CH=NAr2 that are refractory towards Et3Al are activated at room temperature by cerium(IV) compounds. The ethylation takes place selectively at the methine moiety of the imine. The process is strongly influenced by steric hindrance and depends on the electronic nature of the substrate: electron-donating substituents promote the reaction while electron-withdrawing groups cause it to slow down. Application of cerium(IV) ammonium nitrate as promoter gives the best results. In the absence of excess Et3Al it causes, however, transformation of the Schiff base to the corresponding aldehydes and amines.