Substituent effects on regioselective intramolecular oxidation of unactivated C-H bonds: Stereoselective synthesis of substituted tetrahydropyrans
Substituent effects on regioselective intramolecular oxidation of unactivated C-H bonds: Stereoselective synthesis of substituted tetrahydropyrans
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DOI：
10.1021/ja028357l
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发表时间：
2003-01-08
影响因子：
15
通讯作者：
Yang, D
中科院分区：
文献类型：
--
作者：
Wong, MK;Chung, NW;Yang, D
我们以前报道的分子内δ-选择性的C-H键氧化的二环氧乙烷，原位生成的活化酮，提供了一种新的方法来合成四氢吡喃。为了以立体选择性的方式合成取代的四氢吡喃，我们研究了酮的α-，β-和γ-位点上的烷基，氮和氧取代基对分子内C-H键氧化反应的立体选择性的影响。在α-、β-或γ-位点具有甲基的酮1-4显示出与通过考虑过渡态中的空间相互作用预测的反式/顺式比率一致的非对映选择性。此外，酮5和6携带一个庞大的邻苯二甲酰亚胺基在α-和β-网站，分别表现出优异的立体选择性，每个只提供一个非对映异构体。然而，酮9和10轴承β-氧取代基得到相反的立体选择性相比，与β-烷基或氮取代基，可能是因为在过渡态的氢键相互作用。对于酮12和13，无论是轴承甲基和硅烷氧基，氢键相互作用可能是更重要的比空间效应的非对映选择性的分子内氧化的C-H键。
Our previously reported intramolecular delta-selective C-H bond oxidation by dioxiranes, generated in situ from activated ketones, offers a novel approach to the synthesis of tetrahydropyrans. To synthesize substituted tetrahydropyrans in a stereoselective manner, we examined the effects of alkyl, nitrogen, and oxygen substituents at the alpha-, beta-, and gamma-sites of ketones on the stereoselectivities of intramolecular C-H bond oxidation reactions. Ketones 1-4 with a methyl group at the alpha-, beta-, or gamma-site showed the diastereoselectivities that agreed with the trans/cis ratio predicted by considering steric interactions in the transition states. Furthermore, ketones 5 and 6 carrying a bulky phthalimido group at the alpha- and the beta-sites, respectively, exhibited excellent stereoselectivity, each affording only one diastereomer. However, ketones 9 and 10 bearing beta-oxygen substituents gave reversed stereoselectivity as compared to those with beta-alkyl or nitrogen substituents, possibly because of the hydrogen bonding interaction in the transition state. For ketones 12 and 13, both bearing methyl and silyloxy groups, the hydrogen bonding interaction was probably more important than the steric effect on the diastereoselectivity of intramolecular oxidation of C-H bonds.