Chiral-Zn(NTf2)2-complex-catalyzed diastereo- and enantioselective direct conjugate addition of arylacetonitriles to alkylidene malonates

Abstract

Chiral N,N'-dioxide/Zn(NTf2)2 complexes were demonstrated to be highly effective in the direct asymmetric conjugate addition of arylacetonitriles to alkylidene malonates under mild conditions. A wide range of substrates were tolerated to afford their corresponding products in moderate-to-good yields with high diastereoselectivities (82:18->99:1 d.r.) and enantioselectivities (81-99% ee). The reactions performed well, owing to the high Lewis acidity of the metal triflimidate and a ligand-acceleration effect. The N,N'-dioxide also benefited the deprotonation process as a Brønsted base. The catalytic reaction could be performed on the gram-scale with retention of yield, diastereoselectivity, and enantioselectivity. The products that contained functional groups were ready for further manipulation. In addition, a possible catalytic model was proposed to explain the origin of the asymmetric induction.

Keywords: asymmetric catalysis; conjugate addition; enantioselectivity; ligand effects; zinc.