Diastereo- and Enantioselective Synthesis of Quaternary α-Amino Acid Precursors by Copper -Catalyzed Propargylation

A diastereo- and enantioselective propargylic substitution reaction between propargylic carbonates and asubstituted nitroacetates catalyzed by a Cu pybox complex is described. This method allows the preparation of a series of non-proteinogenic quaternary a-amino acid precursors featuring two contiguous stereogenic centers and a terminal alkyne moiety in high yields with good to excellent diastereo- and enantioselectivities in most cases. The propargylated adducts were elaborated into a diverse set of quaternary a -amino acid derivatives.