Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of alpha-Carbamoyl Radicals

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	Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of alpha-Carbamoyl Radicals
	Fang XQ(房新强) ; Liu K(刘鲲) ; Li CZ(李超忠)
刊名	J. Am. Chem. Soc.
	2010
卷号	132 期号:7 页码:2274-2283
ISSN号	0002-7863
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
通讯作者	李超忠
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.
学科主题	有机化学
收录类别	SCI
原文出处	http://dx.doi.org/10.1021/ja9082649
语种	英语
WOS记录号	WOS:000275085100042
公开日期	2013-03-04
内容类型	期刊论文
源URL	[http://202.127.28.38/handle/331003/22862]
专题	上海有机化学研究所_中科院天然产物有机化学重点实验室
推荐引用方式 GB/T 7714	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.
APA	房新强,刘鲲,&李超忠.(2010).Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of alpha-Carbamoyl Radicals.J. Am. Chem. Soc.,132(7),2274-2283.
MLA	房新强,et al."Efficient Regio- and Stereoselective Formation of Azocan-2-ones via 8-Endo Cyclization of alpha-Carbamoyl Radicals".J. Am. Chem. Soc. 132.7(2010):2274-2283.