Enantioselective Stetter Reactions of Enals and Modified Chalcones Catalyzed by N-Heterocyclic Carbenes
作者:Xinqiang Fang、Xingkuan Chen、Hui Lv、Yonggui Robin Chi
DOI:10.1002/anie.201105812
日期:2011.12.2
New trick for an old cat.: Triazolium‐based N‐heterocycliccarbenes (NHCs) catalyze the selective generation of acyl anion equivalents for the title reaction. The stereoelectronic properties of the enal‐derived Breslow intermediates and the unique reactivity of the modified chalcones are crucial for the Stetter reactions to occur. EWG=electron‐ withdrawing group.
Enantioselective Diels–Alder Reactions of Enals and Alkylidene Diketones Catalyzed by N-Heterocyclic Carbenes
作者:Xinqiang Fang、Xingkuan Chen、Yonggui Robin Chi
DOI:10.1021/ol201917u
日期:2011.9.2
introduced to the α-position of chalcones, and the resulting alkylidene diketones showed new reactivities with enals under the catalysis of N-heterocycliccarbenes (NHCs). Selective activation of enals affords enolate equivalents that undergo highly enantioselective intermolecular Diels–Alder reactions with the alkylidene diketones. No products that might have resulted from typical homoenolate pathways were
An efficient diastereo- and enantioselective [3 + 2] cycloaddition of heterosubstituted alkenes with oxiranes via selective C–C bond cleavage of epoxides has been developed. The reaction was catalyzed by a chiral N,N′-dioxide/Ni(II) catalyst, and a variety of chiral highly substituted tetrahydrofurans were obtained in up to 99% yield, 92/8 dr, and 99% ee.
The catalytic asymmetricepoxidation of 2‐arylidene‐1,3‐diketones using aqueous 30% H2O2 as oxidant has been successfully realized by a N,N′‐dioxide–scandium(III) triflate [Sc(OTf)3] complex, giving the corresponding products in moderate to good yields (up to 85%) with excellent enantioselectivities (up to 99% ee) under mild reaction conditions without extra additives.
N,N'-二氧化物-三氟甲磺酸scan [Sc(OTf)3 ]配合物已成功实现了使用30%H 2 O 2水溶液作为氧化剂催化2-亚芳基-1,3-二酮的催化不对称环氧化。,在温和的反应条件下,无需额外的添加剂,即可以中等至良好的收率(高达85%)提供具有良好对映选择性(高达99%ee)的相应产品。
Preparation of Tetrasubstituted Furans via Intramolecular Wittig Reactions with Phosphorus Ylides as Intermediates
作者:Tzu-Ting Kao、Siang-en Syu、Yi-Wun Jhang、Wenwei Lin
DOI:10.1021/ol101080q
日期:2010.7.2
functional furans can be efficiently generated in one step at room temperature within 10 min to 21 h in moderate to high yields (60−99%). The reaction was proposed to proceed via intramolecular Wittig-type reactions, using phosphorus ylides as intermediates.