Planar-chiral pyridine n-oxides, a new family of asymmetric catalysts:: Exploiting an η5-C5Ar5 ligand to achieve high enantioselectivity
Planar-chiral pyridine n-oxides, a new family of asymmetric catalysts:: Exploiting an η5-C5Ar5 ligand to achieve high enantioselectivity
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DOI：
10.1021/ja003573k
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发表时间：
2001-01-17
影响因子：
15
通讯作者：
Fu, GC
中科院分区：
文献类型：
--
作者：
Tao, B;Lo, MMC;Fu, GC
We have recently described a number of applications of planarchiral heterocycles in asymmetric catalysis, both as enantioselective nucleophilic catalysts (eg, 1) 2 and as chiral ligands for transition metals (eg, 2). 3 In each case, nitrogen or phosphorus atoms served as nucleophilic/ligating sites.Catalysts in which oxygen is the nucleophilic site effect a number of useful transformations. 4 For example, pyridine N-oxides catalyze the rearrangement of thiones, as well as the allylation of aldehydes. 5 In view of the utility of planar-chiral pyridine derivatives such as 1, it occurred to us that the corresponding pyridine N-oxides (3) might also prove to be effective asymmetric catalysts. In this report, we describe the synthesis and structural characterization of several planar-chiral pyridine N-oxides, and we apply this new family of complexes to the catalytic enantioselective desymmetrization of meso epoxides (eq 1). In contrast to catalysts in which the pyridine nitrogen serves as the nucleophilic site (eg, 1), we anticipated that, for pyridine N-oxide catalysts, an electron-donating 4-dialkylamino group should not be critical for reactivity. We therefore chose complexes
