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Chang Min Chih‐Tsung Lin Prof. Dr. Daniel Seidel 《Angewandte Chemie (International ed. in English)》2015,54(22):6608-6612
A readily available chiral Brønsted acid was identified as an efficient catalyst for intramolecular Povarov reactions. Polycyclic amines containing three contiguous stereogenic centers were obtained with excellent stereocontrol in a single step from secondary anilines and aldehydes possessing a pendent dienophile. These transformations constitute the first examples of catalytic enantioselective intramolecular aza‐Diels–Alder reactions. 相似文献
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The pyrrolidines 2 and 10 were obtained by thermal ene-reactions at +70° and +180° from the (Z)-4-aza-1, 6-diene 1 and from the (E)-4-aza-1, 6-diene 9 in the ratios of 75:25 and 50:50, respectively. On the other hand, these cyclizations proceeded readily in the presence of diethylaluminum chloride at ? 78° and ? 35° giving in high yield the trans-pyrrolidine 2 from 1 with 100% and from 9 with 89% diastereoselectivity. 相似文献
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Albert Padwa 《Angewandte Chemie (International ed. in English)》1976,15(3):123-136
The intramolecular 1,3-dipolar cycloaddition reaction of suitably functionalized 1,3-dipoles represents a general scheme for the synthesis of novel fused ring heterocycles. Such reactions of a number of 1,3-dipoles are summarized and the general outline and potential analogies for these reactions noted. While the immediate aim of this review is to survey and correlate published work, it is hoped that general and specific points in need of study will be revealed and will stimulate further work in this fertile field. 相似文献
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Wolfgang Oppolzer Victor Snieckus 《Angewandte Chemie (International ed. in English)》1978,17(7):476-486
Thermal cyclizations of appropriate dienes, enynes and related unsaturated systems, some of them carried out on an industrial scale, demonstrate increasingly the preparative power of the intramolecular ene reaction. A variety of substituted, fused and bridged ring systems, including natural products, are thus easily accessible in a regio- and stereo-selective manner. Numerous examples are discussed systematically illustrating the possibilities, limitations, and common features of this cyclization reaction and its reverse ring-opening process. 相似文献
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Dieter Enders Klaus Breuer Jan Runsink J. Henrique Teles 《Helvetica chimica acta》1996,79(7):1899-1902
The first asymmetric intramolecular Stetter reaction is reported, using the chiral triazolium salt 1 as catalyst. Starting from the easily accessible 4-(2-formylphenoxy)but-2-enoates 2 , this protocol opens up an enantioselective pathway to the benzo-annulated pyran-4-ones (chroman-4-ones) 3a–h with good yields and enantiomeric excesses of up to 74%. 相似文献
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Simanenko Yu. S. Popov A. F. Prokop'eva T. M. 《Theoretical and Experimental Chemistry》2003,39(5):288-295
Among hydroxamate ions (typical nucleophiles), anomalously high nucleophilicity relative to 4-nitrophenyl diethyl phosphonate is seen in anions which have general basic catalytic sites that provide anchimeric assistance for proton transfer in the transition state. 相似文献
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Chun‐Xiang Zhuo Prof. Dr. Wei Zhang Prof. Dr. Shu‐Li You 《Angewandte Chemie (International ed. in English)》2012,51(51):12662-12686
This Review summarizes the development of catalytic asymmetric dearomatization (CADA) reactions. The CADA reactions discussed herein include oxidative dearomatization reactions, dearomatization by Diels–Alder and related reactions, the alkylative dearomatization of electron‐rich arenes, transition‐metal‐catalyzed dearomatization reactions, cascade sequences involving asymmetric dearomatization as the key step, and nucleophilic dearomatization reactions of pyridinium derivatives. Asymmetric dearomatization reactions with chiral auxiliaries and catalytic asymmetric reactions of dearomatized substrates are also briefly introduced. This Review intends to provide a concept for catalytic asymmetric dearomatization. 相似文献
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不对称催化环氧化反应 总被引:5,自引:0,他引:5
本文综述了不对称催化环氧化体系的研究进展。重点评述了Sharpless-Kat-suki不对称环氧化反应的特点、机理、新进展与应用,综合分析了由手性(salen)Mn(Ⅲ)催化剂对非功能化烯烃所创建的突出成果与应用前景。 相似文献
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Arup Mukherjee Tamal K. Sen Dr. Pradip Kr. Ghorai Dr. Prinson P. Samuel Dr. Carola Schulzke Dr. Swadhin K. Mandal 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(34):10530-10545
Herein, we report the synthesis and characterization of two organozinc complexes that contain symmetrical phenalenyl (PLY)‐based N,N‐ligands. The reactions of phenalenyl‐based ligands with ZnMe2 led to the formation of organozinc complexes [N(Me),N(Me)‐PLY]ZnMe ( 1 ) and [N(iPr),N(iPr)‐PLY]ZnMe ( 2 ) under the evolution of methane. Both complexes ( 1 and 2 ) were characterized by NMR spectroscopy and elemental analysis. The solid‐state structures of complexes 1 and 2 were determined by single‐crystal X‐ray crystallography. Complexes 1 and 2 were used as catalysts for the intramolecular hydroamination of unactivated primary and secondary aminoalkenes. A combined approach of NMR spectroscopy and DFT calculations was utilized to obtain better insight into the mechanistic features of the zinc‐catalyzed hydroamination reactions. The progress of the catalysis for primary and secondary aminoalkene substrates with catalyst 2 was investigated by detailed kinetic studies, including kinetic isotope effect measurements. These results suggested pseudo‐first‐order kinetics for both primary and secondary aminoalkene activation processes. Eyring and Arrhenius analyses for the cyclization of a model secondary aminoalkene substrate afforded ΔH≠=11.3 kcal mol?1, ΔS≠=?35.75 cal K?1 mol?1, and Ea=11.68 kcal mol?1. Complex 2 exhibited much‐higher catalytic activity than complex 1 under identical reaction conditions. The in situ NMR experiments supported the formation of a catalytically active zinc cation and the DFT calculations showed that more active catalyst 2 generated a more stable cation. The stability of the catalytically active zinc cation was further supported by an in situ recycling procedure, thereby confirming the retention of catalytic activity of compound 2 for successive catalytic cycles. The DFT calculations showed that the preferred pathway for the zinc‐catalyzed hydroamination reactions is alkene activation rather than the alternative amine‐activation pathway. A detailed investigation with DFT methods emphasized that the remarkably higher catalytic efficiency of catalyst 2 originated from its superior stability and the facile formation of its cation compared to that derived from catalyst 1 . 相似文献
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Egle M. Beccalli Prof. Elena Borsini Stefano Brenna Dr. Simona Galli Dr. Micol Rigamonti Gianluigi Broggini Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1670-1678
The isolation of σ‐alkylpalladium Heck intermediates, possible when β‐hydride elimination is inhibited, is a rather rare event. Performing intramolecular Heck reactions on N‐allyl‐2‐halobenzylamines in the presence of [Pd(PPh3)4], we isolated and characterized a series of stable bridged palladacycles containing an iodine or bromine atom on the palladium atom. Indolyl substrates were also tested for isolation of the corresponding complexes. X‐ray crystallographic analysis of one of the indolyl derivatives revealed the presence of a five‐membered palladacycle with the metal center bearing a PPh3 ligand and an iodine atom in a cis position with respect to the nitrogen atom. The stability of the σ‐alkylpalladium complexes is probably a consequence of the strong constraint resulting from the bridged junction that hampers the cisoid conformation essential for β‐hydride elimination. Subsequently, the thus obtained bridged five‐membered palladacycles were proven to be effective precatalysts in Heck reactions as well as in cross‐coupling processes such as Suzuki and Stille reactions. 相似文献