Asymmetric construction of quaternary carbon centers by regio- and enantiocontrolled allylzincation
An allylic zinc reagent bearing a chiral bisoxazoline ligand adds to a substituted cyclopropenone acetal to produce an optically active cyclopropanone acetal possessing a quaternary chiral center in high yield with 97.8-99.8% ee. The steric effects of the bulky bisoxazoline ligand overwhelm the regioselectivity inherent to the electronic property of the olefinic acceptor. High pressure exerts favorable effects on the reaction rate without affecting the high enantio- or regioselectivity.
Nakamura
M
Department of Chemistry, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Inoue
T
Sato
A
Nakamura
E