One-Pot Synthesis of D-Phenylalanine-Functionalized Multiwalled Carbon Nanotubes: A Metal-Free Chiral Material for the Asymmetric Electroreduction of Aromatic Ketones

A simple protocol to synthesize D-phenylalanine (D-PHE)-functionalized multiwalled carbon nanotubes (MWCNTs) via the one-pot method was established by grafting D-PHE onto MWCNTs to obtain D-PHE-MWCNTs under mild reaction conditions. The resulting D-PHE-MWCNTs were characterized in detail via spectroscopy and surface analysis. The electroreduction of 2,2,2-trifluoroacetophenone at the D-PHE-MWCNTs cathode afforded (S)-alpha-(trifluoromethyl) benzyl alcohol whose yield was 65% and the enantiomeric excess was 40%. No extra catalysts were required in this electrochemical reaction solution compared with other reactions requiring homogeneous catalysis. The metal-free chiral material also showed acceptable asymmetric electroreduction performance, considerable stability, and favorable reusability.