Ring expansion of epoxides under Brønsted base catalysis: formal [3+2] cycloaddition of β,γ-epoxy esters with imines providing 2,4,5-trisubstituted 1,3-oxazolidines.
A novel ring-expansion reaction of epoxides under Brønsted base catalysis was developed. The formal [3+2] cycloaddition reaction of β,γ-epoxy esters with imines proceeds in the presence of triazabicyclodecene (TBD) as a superior Brønsted base catalyst to afford 2,4,5-trisubstituted 1,3-oxazolidines in a highly diastereoselective manner. This reaction involves the ring opening of the epoxides with the aid of the Brønsted base catalyst to generate α,β-unsaturated esters having an alkoxide at the allylic position, which would formally serve as a synthetic equivalent of the 1,3-dipole, followed by a cycloaddition reaction with imines in a stepwise fashion. This methodology enables the facile synthesis of enantioenriched 1,3-oxazolidines from easily accessible enantioenriched epoxides.
Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan).
Azusa
A
Kondoh
Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan).
Kenta
K
Odaira
Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan). mterada@m.tohoku.ac.jp.|Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki, Aoba-ku, Sendai 980-8578 (Japan). mterada@m.tohoku.ac.jp.
Masahiro
M
Terada
asymmetric synthesis; brønsted base; cycloaddition; organocatalyst; ring expansion