Helical Chirality Induction by Point Chirality at Helix Terminal

A series of zinc bilinone derivatives bearing a chiral auxiliary at the helix terminal were prepared to investigate the helical chirality induction in the bilinone framework by the point chirality of the chiral auxiliary. Chiral induction was sensitive to the distance to the asymmetric carbon as well as to substituents on the asymmetric carbon. When the chiral carbon was directly attached to the bilinone 19-oxygen and carried an aromatic group, relatively high helical chirality induction was observed in [19-alkoxy-2,7,13,18-tetramethyl-3,8,12,17-tetraethyl-1-bilinonato]zinc(II) as demonstrated by variable-temperature 1 H NMR and CD studies. The ( R )-2-methyl-1-phenylpropanoxy group induced P -helicity in >95% enantiomeric excess at 223 K in CD 2 Cl 2 (ΔΔ G ° ≥ 6.8 kJ/mol).