Synthesis of a C1 symmetric BINOL–terpyridine ligand and highly enantioselective methyl propiolate addition to aromatic aldehydes

A novel C1 symmetric BINOL–terpyridine ligand (R)-5 is synthesized. This ligand in combination with ZnEt2 and Ti(OiPr)4 is found to catalyze the highly enantioselective reaction (up to 98% ee) of methyl propiolate with a variety of aromatic aldehydes at 0 °C to give the synthetically useful γ-hydroxy-α,β-acetylenic esters. In comparison with the previously reported BINOL system, the use of (R)-5 requires a reduced amount of the chiral ligand without the addition of a Lewis base. It shows higher enantioselectivity for a number of substrates.