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.
铈(IV)化合物可在室温下激活对 Et3Al 具有耐受性的希夫碱 Ar1CH=NAr2。乙化作用选择性地发生在
亚胺的甲基上。这一过程受到立体阻碍的强烈影响,并取决于底物的电子性质:供电子的取代基会促进反应,而抽电子的基团则会导致反应减慢。使用
硝酸铵铈(IV)作为
促进剂能产生最佳效果。不过,在没有过量 Et3Al 的情况下,它会导致希夫碱转化为相应的醛和胺。