Unprecedented effects of additives and ligand-to-metal ratio on the enantiofacial selection of copper-catalyzed alkynylation of alpha-imino ester with arylacetylenes

The first catalytic asymmetric addition of arylacetylenes to α-imino esters was carried out using chiral copper(I) complexes as catalysts under mild reaction conditions, providing the corresponding alkynylation products in good yields with 67–74 % ee values. Profound effects of the ligand-to-metal ratio and additives on the stereofacial selection were observed. Both enantiomers of a given product can be obtained with almost identical enantiomeric excess using the same chiral ligand by adjusting the ligand-to-metal ratio.