title: Synthesis of Novel Chiral Diazole Derivative Ligands for the Enantioselective Addition of Diethylzinc to Benzaldehyde.
abstract: The high-pressure-promoted reaction of epoxides with pyrazoles and imidazoles provided access to a variety of chiral diazole derivative ligands such as 11-23. Furthermore, chiral pyrazoles 26 and 27, which have a primary alcohol side chain, were also prepared from (+)-camphopyrazole 4. Each of these chiral diazole ligands was used for the catalytic enantioselective addition of diethylzinc to benzaldehyde. The best results were obtained for 16 and 18: 93% ee was achieved in both cases, and reversed asymmetric induction was observed. A plausible mechanism for this efficient asymmetric induction is offered on the basis of X-ray crystallographic data.
authors.affiliation: Department of Chemistry, Faculty of Science, Kochi University, Akebono-cho, Kochi 780, Japan, and Rigaku Corporation, Matsubara-cho, Akishima, Tokyo 196, Japan.
authors.forename: Hiyoshizo
authors.initials: H
authors.lastname: Kotsuki
authors.forename: Masahiro
authors.initials: M
authors.lastname: Wakao
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Hayakawa
authors.forename: Tomoyasu
authors.initials: T
authors.lastname: Shimanouchi
authors.forename: Motoo
authors.initials: M
authors.lastname: Shiro