Asymmetric Synthesis of β-Lactams through Copper-Catalyzed Alkyne-Nitrone Coupling with a Prolinol-Phosphine Chiral
Yurie Takayama1, Takaoki Ishii1, Hirohisa Ohmiya1
1Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo, 060-0810, Japan.
Abstract:
Prolinol-phosphine chiral ligands enabled highly enantioselective copper-catalyzed intermolecular alkyne-nitrone coupling (Kinugasa reaction) to produce 1,3,4-trisubstituted chiral β-lactams. A high level of enantiocontrol was achieved not only with aryl- or alkenylacetylenes but also with alkylacetylenes, which were important but unfavorable substrates in the previously reported protocols. Two-point hydrogen bonding between the chiral ligand and the nitrone oxyanion consisting of O-H⋅⋅⋅O and C(sp3 )-H⋅⋅⋅O hydrogen bonds is proposed.
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