Conjugate addition of aromatic amines to ethenetricarboxylates

The conjugate addition of amines is considered to be a useful reaction in synthetic organic chemistry. The reaction of reactive electrophilic olefins, ethenetricarboxylates, and aromatic amines with and without catalytic Lewis acids such as ZnCl2 and ZnBr2 at room temperature gave amine adducts in high yields. The products were converted to α-amino acid, dl-aspartic acid derivatives. Using Lewis acids such as Sc(OTf)3 and Zn(OTf)2 at higher temperature (40-80 °C), the reaction of ethenetricarboxylates and N-methylaniline gave an aromatic substitution product. A catalytic enantioselective conjugate addition using a chiral Lewis acid was also investigated. For example, the reaction of 1,1-diethyl 2-tert-butyl ethenetricarboxylate with N-methylaniline in the presence of chiral bisoxazoline-Cu(II) complex in THF at −20 °C for 17 h gave an amine adduct in 91% yield and 78% ee. On the other hand, the reaction with aniline and primary aniline derivatives gave adducts with almost no ee%.

Graphical abstractDownload full-size imageThe reaction of ethenetricarboxylates 1 and aromatic amines with and without catalytic Lewis acids gave amine adducts or aromatic substitution products, depending on the conditions.