Asymmetric N-Heterocyclic Carbene-catalyzed [4+2] Cycloaddition of Ketenes with alpha-cyanochalcones

doi:10.6023/A14040334

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	Asymmetric N-Heterocyclic Carbene-catalyzed [4+2] Cycloaddition of Ketenes with alpha-cyanochalcones
	Sun Lihui; Liang Zhiqin; Ye Song
刊名	ACTA CHIMICA SINICA
	2014-07-15
卷号	72 期号:7 页码:841-844
关键词	N-heterocyclic Carbenes [4+2] Cycloaddition Asymmetric Catalysis Dihydropyranones
ISSN号	0567-7351
DOI	10.6023/A14040334
英文摘要	The N-heterocyclic carbene (NHC)-catalyzed enantioselective cycloaddition reactions of ketenes are powerful methods for the synthesis of chiral heterocycles. Followed by the previous reported NHC-catalyzed [2+2] and [4+2] cycloaddtion of ketenes with imines, ketones and various heterodienes, the NHC-catalyzed enantioselective [4+2] cycloaddition of ketenes with alpha-cyanochalcones was investigated in this paper. In the presence of the bulky N-heterocyclic carbene derived from L-pyrogutamic acid, the reaction of ketenes with alpha-cyanochalcones went smoothly, giving the corresponding chiral multisubstituted dihydropyranones in good yields with good diastereoselectivities and high enantioselectivities. Initially, several NHCs derived from L-pyrogultamic acids were screened for the reaction. The NHC 4b with bulkyl dimethyl(tert-butyl)silyl group and N-isopropylphenyl performed better than others. The reaction catalyzed by NHCs 4c similar to 4d with a free hydroxyl group gave the dihydropyranones with reversed diastereoselectivity but decreased enantioselectivity. The reaction went well in THF, toluene, dichloromethane or ether, while the one in toluene showed best results. Better yield was reached when the reaction was carried out at 0 or -20 degrees C. Under optimized reaction conditions, a variety of aryl(alkyl)ketenes were investigated for the reaction. It was found that both electron-donating and electron-withdrawing groups in the aryl(alkyl)ketene are tolerable for the reaction. The one with electron-withdrawing substituent gave the product in better yield and diastereoselectivity, while the one with electron-donating substituent resulted in better enantioselectivity. The alkyl chain of the ketenes could be ethyl, n-propyl and n-butyl. All the alpha-cyanochalcones with para-, meta- or ortho-substitutent went well for the reaction. The absolute configuration of resulted dihydropyranone 3e was established by the X-ray analysis of its crystal. The reaction is proposed to initialize with the addition of NHC to ketenes to give the enolate I. The adduct II is formed from enolate I and alpha-cyanochalcone via stepwise Michael addition and cyclization or simultaneous Diels-Alder reaction. The elimination of NHC from adduct II gives final dihydropyranone 3.
语种	英语
出版者	SCIENCE PRESS
WOS记录号	WOS:000340842000012
内容类型	期刊论文
源URL	[http://ir.iccas.ac.cn/handle/121111/52463]
专题	中国科学院化学研究所
通讯作者	Sun Lihui
作者单位	Chinese Acad Sci, Inst Chem, CAS Key Lab Mol Recognit & Funct, Beijing Natl Lab Mol Sci, Beijing 100190, Peoples R China
推荐引用方式 GB/T 7714	Sun Lihui,Liang Zhiqin,Ye Song. Asymmetric N-Heterocyclic Carbene-catalyzed [4+2] Cycloaddition of Ketenes with alpha-cyanochalcones[J]. ACTA CHIMICA SINICA,2014,72(7):841-844.
APA	Sun Lihui,Liang Zhiqin,&Ye Song.(2014).Asymmetric N-Heterocyclic Carbene-catalyzed [4+2] Cycloaddition of Ketenes with alpha-cyanochalcones.ACTA CHIMICA SINICA,72(7),841-844.
MLA	Sun Lihui,et al."Asymmetric N-Heterocyclic Carbene-catalyzed [4+2] Cycloaddition of Ketenes with alpha-cyanochalcones".ACTA CHIMICA SINICA 72.7(2014):841-844.