DFT and Experimental Exploration of the Mechanism of InCl3-Catalyzed Type II Cycloisomerization of 1,6-Enynes: Identifying InCl2+ as the Catalytic Species and Answering Why Nonconjugated Dienes Are Generated

doi:10.1021/jo301471w

CORC > 化学研究所 > 中国科学院化学研究所

	DFT and Experimental Exploration of the Mechanism of InCl3-Catalyzed Type II Cycloisomerization of 1,6-Enynes: Identifying InCl2+ as the Catalytic Species and Answering Why Nonconjugated Dienes Are Generated
	Zhuo, Lian-Gang; Zhang, Ji-Ji; Yu, Zhi-Xiang
刊名	JOURNAL OF ORGANIC CHEMISTRY
	2012-10-05
卷号	77 期号:19 页码:8527-8540
ISSN号	0022-3263
DOI	10.1021/jo301471w
英文摘要	InCl3 and other In(III) species have been widely applied as catalysts in many reactions. However, what are the real catalytic species of these reactions? Through DFT calculations and experimental investigation of the mechanism and regioselectivity of InCl3-catalyzed cycloisomerization reactions of 1,6-enynes (here all discussed 1,6-enynes are ene-internal-alkyne molecules), we propose that the catalytic species of this reaction is the in situ generated InCl2+. Further electrospray ionization high-resolution mass spectroscopy (ESI-HRMS) supported the existence of InCl2+ in acetonitrile solution. This finding of InCl2+ as the catalytic species suggests that other reactions catalyzed by In(III) species could also have cationic In(III) species as the real catalysts. DFT calculations revealed that the catalytic cycle of the cycloisomerization of 1,6-enynes catalyzed by InCl3 starts from InCl2+. coordination to the alkyne of the substrate, generating a vinyl cation. Then nonclassical cyclopropanation of the vinyl cation to the alkene part of the substrate gives a homoallylic cation, which undergoes a novel homoallylic cation rearrangement involving a [1,3]-carbon shift to give the more stable homoallylic cation 15. Finally InCl2+ cation coordination assisted nonconjugated [1,2]-hydride shifts deliver the final nonconjugated diene products. The preference of generating nonconjugated dienes instead of conjugated dienes in the cycloisomerization reaction is mainly due to two reasons: coordination of the InCl2+ to the alkene part in [1,2]-H shift transition states disfavors the conjugated [1,2]-H shifts that generate cations adjacent to the positively charged alkene, and coordination of InCl2+ to the nonconjugated diene product is stronger than coordination to the conjugated diene, making nonconjugated [1,2]-H shift transition states lower in energy than conjugated [1,2]-H shift transition states, on the basis of the Hammond postulate. DFT calculations predicted that the conjugated [1,2]-H shifts could become favored if the electron-donating methyl substituent in the alkyne moiety of the 1,6-enyne is replaced by a H atom. This prediction of producing a conjugated diene has been verified experimentally. Rationalization about why type H rather than type I products were obtained using InCl3 as the catalyst in the cycloisomerization of 1,6-enynes has also been investigated computationally.
语种	英语
出版者	AMER CHEMICAL SOC
WOS记录号	WOS:000313767800016
内容类型	期刊论文
源URL	[http://ir.iccas.ac.cn/handle/121111/47533]
专题	中国科学院化学研究所
通讯作者	Yu, Zhi-Xiang
作者单位	Peking Univ, Beijing Natl Lab Mol Sci BNLMS, Key Lab Bioorgan Chem & Mol Engn, Minist Educ,Coll Chem, Beijing 100871, Peoples R China
推荐引用方式 GB/T 7714	Zhuo, Lian-Gang,Zhang, Ji-Ji,Yu, Zhi-Xiang. DFT and Experimental Exploration of the Mechanism of InCl3-Catalyzed Type II Cycloisomerization of 1,6-Enynes: Identifying InCl2+ as the Catalytic Species and Answering Why Nonconjugated Dienes Are Generated[J]. JOURNAL OF ORGANIC CHEMISTRY,2012,77(19):8527-8540.
APA	Zhuo, Lian-Gang,Zhang, Ji-Ji,&Yu, Zhi-Xiang.(2012).DFT and Experimental Exploration of the Mechanism of InCl3-Catalyzed Type II Cycloisomerization of 1,6-Enynes: Identifying InCl2+ as the Catalytic Species and Answering Why Nonconjugated Dienes Are Generated.JOURNAL OF ORGANIC CHEMISTRY,77(19),8527-8540.
MLA	Zhuo, Lian-Gang,et al."DFT and Experimental Exploration of the Mechanism of InCl3-Catalyzed Type II Cycloisomerization of 1,6-Enynes: Identifying InCl2+ as the Catalytic Species and Answering Why Nonconjugated Dienes Are Generated".JOURNAL OF ORGANIC CHEMISTRY 77.19(2012):8527-8540.