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学科主题: 有机化学
题名: Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of alpha-Carbamoyl Radicals
其他题名: 由α-酰胺基自由基8-endo环合反应高效及区域和立体选择性地合成八元环内酰胺
作者: Fang XQ(房新强) ; Liu K(刘鲲) ; Li CZ(李超忠)
通讯作者: 李超忠
刊名: J. Am. Chem. Soc.
发表日期: 2010
卷: 132, 期:7, 页:2274-2283
收录类别: SCI
部门归属: 中国科学院上海有机化学研究所
英文摘要: The iodine-atom-transfer 8-endo cyclization of alpha-carbamoyl radicals was investigated experimentally and theoretically. With the aid of Mg(ClO4)(2) and a bis(oxazoline) ligand, N-ethoxycarbonyl-substituted N-(pent-4-enyl)-2-iodoalkanamides underwent 8-endo cyclization leading to the formation of only the corresponding 3,5-trans-substituted azocan-2-ones in excellent yields Similarly, the BF3 center dot OEt2/H2O-promoted reactions of N-ethoxycarbonyl-N-(2-allylaryl)-2-iodoalkanamides afforded exclusively the benzazocanone products with a 3,5-cis configuration in high yields The bidentate chelation of substrate radicals not only significantly improved the efficiency of cyclization but also resulted in the change of stereochemistry of azocanone products from 3,8-trans to 3,8-cis Theoretical calculations at the UB3LYP/6-31G* level revealed that the cyclization of N-carbonyl-substituted alpha-carbamoyl radicals occurs via the E-conformational transition states without the presence of a Lewis acid. On the other hand, the cyclization proceeds via the Z-conformational transition states when the substrates form the bidentate chelation with a Lewis acid In both cases, the 8-endocyclization is always fundamentally preferred over the corresponding 7-exo cyclization The complexed radicals having the more rigid conformations also allow the better stereochemical control in the iodine-atom-abstraction step To further understand the reactivity of alpha-carbamoyl radicals, the competition between the 8-endo and 5-exo cyclization was also studied The results demonstrated that the 8-endo cyclization is of comparable rate to the corresponding 5-exo cyclization for alpha-carbamoyl radicals with fixed Z-conformational transition states As a comparison, the 8-endo mode is fundamentally preferred over the 5-exo mode in the cyclization of INIH-amide substrates because the latter requires the Z-conformational transition states, whereas the former proceeds via the more stable E-conformational transition states.
语种: 英语
相关网址: 查看原文
WOS记录号: WOS:000275085100042
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内容类型: 期刊论文
URI标识: http://ir.sioc.ac.cn/handle/331003/22862
Appears in Collections:中科院天然产物有机化学重点实验室_期刊论文

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Recommended Citation:
Fang XQ,Liu K,Li CZ. Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of alpha-Carbamoyl Radicals[J]. J. Am. Chem. Soc.,2010,132(7):2274-2283.
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