Synthesis of novel chiral bis(2-oxazolinyl)xanthene (xabox) ligands and their evaluation in catalytic asymmetric 1,3-dipolar cycloaddition reactions of nitrones with 3-crotonoyl-2-oxazolidinone |
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| Authors: | Seiji Iwasa Yosuke Ishima Katsuyuki Aoki |
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| Institution: | a School of Materials Science, Toyohashi University of Technology, Tempaku-cho, Toyohashi, Aichi 441-8580, Japan
b Graduate School of Engineering, Department of Applied Chemistry, Nagoya University, Chikusa, Nagoya, Aichi 464-8603, Japan |
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| Abstract: | Chiral 4,5-bis(2-oxazolinyl)-(2,7-di-tert-butyl-9,9-dimethyl)-9H-xanthenes (xabox) were synthesized and the chiral environments were evaluated in catalytic asymmetric 1,3-dipolar cycloaddition reactions of nitrones resulting in good to excellent enantioselectivities. 1,3-Dipolar cycloaddition reactions of nitrones with 3-crotonoyl-2-oxazolidinone in the presence of a bis(2-oxazolinyl)xanthene (4c; xabox-Bn) and Mn(II) or Mg(II) complex as a chiral Lewis acid catalyst proceeded smoothly to give the corresponding cycloadducts ranging from 96:4 to >99:1 of endo:exo ratio and ranging from 91% to 98% ee for the endo adduct. |
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| Keywords: | 1 3-Dipolar cycloaddition Nitrone Molecular catalyst Xanthene backbone Nitrogen ligand |
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