期刊
TETRAHEDRON
卷 64, 期 8, 页码 1813-1822出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2007.11.109
关键词
1,3-dipolar cycloaddition; chiral ligand; Diels-Alder reaction; oxazoline; xanthene
A series of chiral 4,5-bis(2-oxazolinyl)-(2,7-di-tei-t-butyl-9,9-dimethyl)-9H-xanthenes (xabox) and their transition-metal complexes were synthesized. The X-ray analysis of xabox-RhCl3 complex shows a unique facial type structure. Xabox-Bn-Mn(II) and xabox-Bn-Mg(II) complexes were found to be efficient catalysts in nitrone 1,3-dipolar cycloaddition (1,3-D.C.) reaction resulting in good to excellent enantioselectivities ranging from 96:4 to > 99: 1 of endolexo ratio and 91-96% ee for the endo adduct. The correlation between enantiomeric excess of the ligand and the product in the nitrone 1,3-D.C. reaction shows a clear linear relationship, which suggests xabox-metal catalyst worked as a single molecular catalyst. In addition, xabox-i-Pr-Mn(II) complex was also found to be an active catalyst for Diels-Alder (D-A) reaction of acryloyloxazolidinone and cyclopentadiene affording the corresponding cycloadduct in quantitative yield along with 82% ee and 98:2 endolexo ratio. (C) 2007 Elsevier Ltd. All rights reserved.
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