Synthesis of Novel Chiral Diazole Derivative Ligands for the Enantioselective Addition of Diethylzinc to Benzaldehyde.
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.
Kotsuki
Hiyoshizo
H
Department of Chemistry, Faculty of Science, Kochi University, Akebono-cho, Kochi 780, Japan, and Rigaku Corporation, Matsubara-cho, Akishima, Tokyo 196, Japan.
Wakao
Masahiro
M
Hayakawa
Hiroyuki
H
Shimanouchi
Tomoyasu
T
Shiro
Motoo
M