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1.
An Alkene‐Promoted Borane‐Catalyzed Highly Stereoselective Hydrogenation of Alkynes to Give Z‐ and E‐Alkenes 下载免费PDF全文
Dr. Yongbing Liu Lianrui Hu Prof. Dr. Hui Chen Prof. Dr. Haifeng Du 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(8):3495-3501
The stereoselective hydrogenation of alkynes to alkenes is an extremely useful transformation in synthetic chemistry. Despite numerous reports for the synthesis of Z‐alkenes, the hydrogenation of alkynes to give E‐alkenes is still not well resolved. In particular, selective preparation of both Z‐ and E‐alkenes by the same catalytic hydrogenation system using molecular H2 has rarely been reported. In this paper, a novel strategy of using simple alkenes as promoters for the HB(C6F5)2‐catalyzed metal‐free hydrogenation of alkynes was adopted. Significantly, both Z‐ and E‐alkenes can be furnished by hydrogenation with molecular H2 in high yields with excellent stereoselectivities. Further experimental and theoretical mechanistic studies suggest that interactions between H and F atoms of the alkene promoter, borane intermediate, and H2 play an essential role in promoting the hydrogenolysis reaction. 相似文献
2.
Catalyst‐Enabled Site‐Divergent Stereoselective Michael Reactions: Overriding Intrinsic Reactivity of Enynyl Carbonyl Acceptors 下载免费PDF全文
Dr. Daisuke Uraguchi Ryo Shibazaki Naoya Tanaka Kohei Yamada Dr. Ken Yoshioka Prof. Dr. Takashi Ooi 《Angewandte Chemie (International ed. in English)》2018,57(17):4732-4736
A site‐divergent stereoselective Michael reaction system is developed based on the identification of two distinct catalysts. Cinchonidine‐derived thiourea catalyzes the 1,4‐addition of prochiral azlactone enolates to enynyl N‐acyl pyrazoles in a highly diastereo‐ and enantioselective manner to give stereochemically defined alkynes, while P‐spiro chiral triaminoiminophosphorane catalytically controls the stereoselective 1,6‐addition and the consecutive γ‐protonation of the vinylogous enolate intermediate to afford Z,E‐configured conjugated dienes. This 1,6‐adduct serves as a valuable precursor for the synthesis of a 2‐amino‐2‐deoxy sugar. 相似文献
3.
Nickel‐Catalyzed Synthesis of N‐Aryl‐1,2‐dihydropyridines by [2+2+2] Cycloaddition of Imines with Alkynes through T‐Shaped 14‐Electron Aza‐Nickelacycle Key Intermediates 下载免费PDF全文
Dr. Yoichi Hoshimoto Tomoya Ohata Dr. Masato Ohashi Prof. Dr. Sensuke Ogoshi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):4105-4110
Despite there being a straightforward approach for the synthesis of 1,2‐dihydropyridines, the transition‐metal‐catalyzed [2+2+2] cycloaddition reaction of imines with alkynes has been achieved only with imines containing an N‐sulfonyl or ‐pyridyl group. Considering the importance of 1,2‐dihydropyridines as useful intermediates in the preparation of a wide range of valuable organic molecules, it would be very worthwhile to provide novel strategies to expand the scope of imines. Herein we report a successful expansion of the scope of imines in nickel‐catalyzed [2+2+2] cycloaddition reactions with alkynes. In the presence of a nickel(0)/PCy3 catalyst, a reaction with N‐benzylidene‐P,P‐diphenylphosphinic amide was developed. Moreover, an application of N‐aryl imines to the reaction was also achieved by adopting N‐heterocyclic carbene ligands. The isolation of an (η2‐N‐aryl imine)nickel(0) complex containing a 14‐electron nickel(0) center and a T‐shaped 14‐electron five‐membered aza‐nickelacycle is shown. These would be considered as key intermediates of the reaction. The structure of these complexes was unambiguously determined by NMR spectroscopy and X‐ray analyses. 相似文献
4.
A novel method for the stereoselective synthesis of (Z)‐4‐(2‐bromovinyl)benzenesulfonyl azide by simultaneous azidation and debrominative decarboxylation of anti‐2,3‐dibromo‐3‐(4‐chlorosulfonylphenyl)propanoic acid using NaN3 only was developed. Facile transformation of (Z)‐4‐(2‐bromovinyl)benzenesulfonyl azide to (Z)‐N‐[4‐ (2‐bromovinyl)benzenesulfonyl]imidates was also achieved by Cu‐catalyzed three‐component coulping of (Z)‐4‐(2‐bromovinyl)benzenesulfonyl azide, terminal alkynes and alcohols/phenols. 相似文献
5.
Venkata Krishna Reddy Motakatla Anusha Gokanapalli Vasu Govardhana Reddy Peddiahgari 《应用有机金属化学》2019,33(11)
A series of new benzimidazolium chlorides bearing N,N′‐benzyl, 2,4,6‐trimethylbenzyl and 2,4,6‐triisopropylbenzyl substituents have been designed and synthesized from various o‐phenylenediamines. Subsequently, corresponding Cu‐based N‐heterocyclic carbenes (NHCs) were generated in situ in the reaction medium which represents a new application of NHCs exploiting distinct catalytic property towards intermolecular cyclization reaction cascade for the synthesis of 2‐aryl‐3‐(arylethynyl)quinoxalines from o‐phenylenediamines and terminal alkynes. The outcome of the cyclization reaction product depends upon the N,N′‐substituents present on the benzimidazolium chlorides. 相似文献
6.
A [4+1] Cyclative Capture Approach to 3H‐Indole‐N‐oxides at Room Temperature by Rhodium(III)‐Catalyzed CH Activation 下载免费PDF全文
Dr. Yaxi Yang Xuan Wang Dr. Yuanchao Li Dr. Bing Zhou 《Angewandte Chemie (International ed. in English)》2015,54(51):15400-15404
The rhodium(III)‐catalyzed [3+2] C? H cyclization of aniline derivatives and internal alkynes represents a useful contribution to straightforward synthesis of indoles. However, there is no report on the more challenging synthesis of pharmaceutically important N‐hydroxyindoles and 3H‐indole‐N‐oxides. Reported herein is the first rhodium(III)‐catalyzed [4+1] C? H oxidative cyclization of nitrones with diazo compounds to access 3H‐indole‐N‐oxides. More significantly, this reaction proceeds at room temperature and has been extended to the synthesis of N‐hydroxyindoles and N‐hydroxyindolines. 相似文献
7.
A new cross‐coupling reaction of N‐benzylic sulfonamides with terminal alkynes for the synthesis of internal alkynes is reported. In the presence of 5 mol% of (Tf)2NH/Bi(OTf)3 (1:1), a broad range of N‐benzylic sulfonamides react smoothly with arylacetylenes to afford structurally diverse internal alkynes in moderate to excellent yields. We reasoned that vinyl cations could be formed by the regioselective attack of terminal alkynes with benzyl cations generated in situ from N‐benzylic sulfonamides under acidic conditions, which then eliminated to form a carbon‐carbon triple bond. 相似文献
8.
Takasuke Mukaiyama Dr. Hayato Ishikawa Dr. Hiroyuki Koshino Prof. Dr. Yujiro Hayashi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(52):17789-17800
The one‐pot sequential synthesis of (?)‐oseltamivir has been achieved without evaporation or solvent exchange in 36 % yield over seven reactions. The key step was the asymmetric Michael reaction of pentan‐3‐yloxyacetaldehyde with (Z)‐N‐2‐nitroethenylacetamide, catalyzed by a diphenylprolinol silyl ether. The use of a bulky O‐silyl‐substituted diphenylprolinol catalyst, chlorobenzene as a solvent, and HCO2H as an acid additive, were key to produce the first Michael adduct in both excellent yield and excellent diastereo‐ and enantioselectivity. Investigation into the effect of acid demonstrated that an acid additive accelerates not only the E–Z isomerization of the enamines derived from pentan‐3‐yloxyacetaldehyde with diphenylprolinol silyl ether, but also ring opening of the cyclobutane intermediate and the addition reaction of the enamine to (Z)‐N‐2‐nitroethenylacetamide. The transition‐state model for the Michael reaction of pentan‐3‐yloxyacetaldehyde with (Z)‐N‐2‐nitroethenylacetamide was proposed by consideration of the absolute configuration of the major and minor isomers of the Michael product with the results of the Michael reaction of pentan‐3‐yloxyacetaldehyde with phenylmaleimide and naphthoquinone. 相似文献
9.
Reactivity of N,N″‐1,ω‐alkanediyl‐bis‐[N′‐organylthiourea] Derivatives Towards Isatylidene Malononitrile 下载免费PDF全文
Alaa A. Hassan Kamal M. A. El‐Shaieb Amal S. Abd El‐Aal Stefan Bräse Martin Nieger 《Journal of heterocyclic chemistry》2016,53(6):2025-2029
(Z)‐2‐(2‐Oxoindolin‐3‐ylidene)‐2‐(substituted amino)acetonitriles, 2‐thioxoimidazolidine‐1‐carbothioamides, and 2‐thioxotetrahydropyrimidine‐1(2H)‐carbothioamides were synthesized via conventional thermal or microwave‐assisted reaction of isatylidene malononitrile with N,N″‐1,ω‐alkanediyl‐bis‐[N′‐organylthiourea] derivatives. Rationale for these conversations involving the nucleophilic addition on the dicyanomethylene carbon atom and intramolecular heterocyclization of the title compounds is presented. The structure of the (Z)‐2‐(2‐oxoindolin‐3‐ylidene)‐2‐(phenylamino)acetonitrile has been confirmed by the X‐ray analysis. 相似文献
10.
Chiral N,N′‐Dioxide‐Organocatalyzed Regio‐, Diastereo‐ and Enantioselective Michael Addition–Alkylation Reaction 下载免费PDF全文
Juhua Feng Xiao Yuan Weiwei Luo Dr. Lili Lin Prof. Dr. Xiaohua Liu Prof. Dr. Xiaoming Feng 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15650-15653
A highly regio‐, diastereo‐ and enantioselective Michael addition–alkylation reaction between α‐substituted cyano ketones and (Z)‐bromonitrostyrenes has been realized by using a chiral N,N′‐dioxide as organocatalyst. A variety of substrates performed well in this reaction, and the corresponding multifunctionalized chiral 2,3‐dihydrofurans were obtained in up to 95 % yield with 95:5 dr and 93 % ee. 相似文献
11.
Masaki Shimoi Takashi Watanabe Prof. Katsuhiro Maeda Prof. Dennis P. Curran Dr. Tsuyoshi Taniguchi 《Angewandte Chemie (International ed. in English)》2018,57(30):9485-9490
Hydroboration of internal alkynes with N‐heterocyclic carbene boranes (NHC‐boranes) occurs to provide stable NHC (E)‐alkenylboranes upon thermolysis in the presence of di‐tert‐butyl peroxide. The E isomer results from an unusual trans‐hydroboration, and the E/Z selectivity is typically high (90:10 or greater). Evidence suggests that this hydroboration occurs by a radical‐chain reaction involving addition of an NHC‐boryl radical to an alkyne to give a β‐NHC‐borylalkenyl radical. Ensuing hydrogen abstraction from the starting NHC‐borane provides the product and returns the starting NHC‐boryl radical. Experiments suggest that the observed trans‐selectivity results from kinetic control in the hydrogen‐transfer reaction. 相似文献
12.
《Journal of heterocyclic chemistry》2017,54(6):3071-3076
An efficient method for the synthesis of N‐alkylated 2‐(4‐substituted‐1H‐1,2,3‐triazol‐1‐yl)‐1H‐indole‐3‐carbaldehyde has been developed starting from oxindole and indole using Huisgen's 1,3‐dipolar cycloaddition reaction of organic azides to alkynes. The effect of catalysts and solvent on these reactions has been investigated. Among all these conditions, while using CuSO4·5H2O, DMF was found to be the best system for this reaction. It could also be prepared in a one‐pot three‐component manner by treating equimolar quantities of halides, azides, and alkynes. The Huisgen's 1,3‐dipolar cycloaddition reaction was performed using CuSO4·5H2O in DMF with easy work‐up procedure. 相似文献
13.
Masilamani Jeganmohan Dr. Sivakolundu Bhuvaneswari Dr. Chien‐Hong Cheng Prof. Dr. 《化学:亚洲杂志》2010,5(1):153-159
The reaction of benzynes with N‐heteroaromatics including quinolines, isoquinolines, and pyridines and various terminal alkynes or ketones with an α‐hydrogen in the presence of KF and 18‐crown‐6 in THF at room temperature for 8 h gave various N‐arylated 1,2‐dihydroheteroaromatics in good to moderate yields. Some of these product structures are found in various naturally occurring and biologically active heterocyclic compounds. The reaction involves an unusual multiple construction of new C? C, C? N, and C? H bonds and the cleavage of a C? H bond in one pot. It is likely that the three‐component coupling proceeds through the nucleophilic addition of quinoline to benzyne, which generates a zwitterionic species. The latter then attracts a proton from terminal alkyne (or ketone) to generate an N‐arylated quinolinium cation and an acetylide anion. Further reaction of these two ions provides the final substituted 1,2‐dihydroquinolines. In the reaction, the terminal alkyne acts first as a proton donor and then as a nucleophile. The application of a three‐component coupling reaction product, 1,2‐dihydro‐2‐pyridinyl alkyne in a stereospecific [4+2] Diels–Alder cycloaddition reaction with N‐phenyl maleimide to give an isoquinuclidine derivative, an important core present in various natural products, is demonstrated. 相似文献
14.
An intermolecular two C? C bond formation procedure for the synthesis of carbocycles mediated by hypervalent iodine(III) reagents was developed. This metal free protocol provided a new approach for the synthesis of useful substituted 1‐amino‐2‐naphthoic acid derivatives via benzannulation reactions. Various N‐unsubstituted and N‐alkyl substituted aromatic enamines with terminal alkynes and non‐terminal alkynes can be converted into corresponding 1‐amino‐2‐naphthoic acid derivatives under mild reaction conditions. When meta‐substituted phenyl enamines were employed in the reaction, two cyclization paths were detected in the reaction and ortho‐cyclization products were the only or major products. Good functional group tolerance, readily available material and high atom utilization efficiency make this method a potential procedure which may find broad application in organic synthesis. 相似文献
15.
A syn‐Selective Aza‐Aldol Reaction of Boron Aza‐Enolates Generated from N‐Sulfonyl‐1,2,3‐Triazoles and 9‐BBN‐H 下载免费PDF全文
Dr. Tomoya Miura Takayuki Nakamuro Sho Miyakawa Prof. Dr. Masahiro Murakami 《Angewandte Chemie (International ed. in English)》2016,55(30):8732-8735
A syn‐selective aza‐aldol reaction of boron aza‐enolates, generated from N‐sulfonyl‐1,2,3‐triazoles and 9‐BBN‐H, is reported. It provides a sequential one‐pot procedure for the stereoselective construction of 1,3‐amino alcohols, having contiguous stereocenters, starting from terminal alkynes. 相似文献
16.
Solvent‐Dependent Asymmetric Synthesis of Alkynyl and Monofluoroalkenyl Isoindolinones by CpRhIII‐Catalyzed C−H Activation 下载免费PDF全文
Teng Li Chao Zhou Xiaoqiang Yan Prof. Dr. Jun Wang 《Angewandte Chemie (International ed. in English)》2018,57(15):4048-4052
The asymmetric synthesis of alkynyl and monofluoroalkenyl isoindolinones from N‐methoxy benzamides and α,α‐difluoromethylene alkynes is enabled by C?H activation with a chiral CpRhIII catalyst. Remarkably, product formation is solvent‐dependent; alkynyl isoindolinones are afforded in MeOH (up to 86 % yield, 99.6 % ee) whereas monofluoroalkenyl isoindolinones are generated in iPrCN (up to 98:2 Z/E, 93 % yield, 86 % ee). Mechanistic studies revealed chiral allene and E‐configured alkenyl rhodium species as reaction intermediates. The latter is transformed into the corresponding Z‐configured monofluoroalkene upon protonation in the iPrCN system and into an alkyne by an unusual anti β‐F elimination in the MeOH system. Notably, kinetic resolution processes occur in this reaction. Despite the moderate enantiocontrol for the formation of the chiral allene, the Z‐monofluoroalkenyl isoindolinones and alkynyl isoindolinones were obtained in good enantiopurities by one or two sequential kinetic resolution processes. 相似文献
17.
Excellent yields were obtained from the silver nitrate‐catalyzed homocoupling reaction of alkynes in N,N‐dimethylformamide using triphenylphosphine as ligand. This safe and simple silver catalytic system has been employed in a safe and efficient protocol for the synthesis of various 1,3‐diyne products from the corresponding aromatic or aliphatic alkynes with good air stability and absence of side products. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
18.
Mohammad Navid SoltaniRad Ali Khalafi‐Nezhad Somayeh Babamohammadi Somayeh Behrouz 《Helvetica chimica acta》2010,93(12):2454-2466
A convenient and efficient method for a one‐pot conversion of N‐alkylisatins to N‐alkylisatin O‐alkyloximes 7a – 7n as potential chemotherapeutic agents is described (Scheme) (isatin=1H‐indole‐2,3‐dione). In this method, the microwave‐assisted three‐component reaction of N‐alkylisatins 8 , hydroxylamine hydrochloride, and diverse alkyl halides in the presence of K2CO3 and Bu4NBr furnishes the corresponding N‐alkylisatin O‐alkyloximes under solvent‐free condition in short times (2–10 min) and good to excellent yields (62–83%). The O‐alkylation of in situ generated isatin oximes with alkyl halides was achieved regioselectively, and (Z)‐O‐alkyloximes were produced dominantly. PM3 Semi‐empirical quantum‐mechanic calculations were performed to rationalize the evidences, and the calculations indicated a lower heat of formation for the (Z)‐O‐alkyloximes. 相似文献
19.
Density functional calculations have been performed to comparatively investigate two possible pathways of Au(I)‐catalyzed Conia‐ene reaction of β‐ketoesters with alkynes. Our studies find that, under the assistance of trifluoromethanesulfonate (TfO), the β‐ketoester is the most likely to undergo Model II to isomerize into its enol form, in which TfO plays a proton transfer role through a 6‐membered ring transition state. The coordination of the Au(I) catalyst to the alkynes triple bond can enhance the eletrophilic capability and reaction activity of the alkynes moiety, which triggers the nucleophilic addition of the enol moiety on the alkynes moiety to give a vinyl‐Au intermediate. This cycloisomerizaion step is exothermal by 21.3 kJ/mol with an energy barrier of 56.0 kJ/mol. In the whole catalytic process, the protonation of vinyl‐Au is almost spontaneous, and the formation of enol is a rate‐limiting step. The generation of enol and the activation of Au(I) catalyst on the alkynes are the key reasons why the Conia‐ene reaction can occur in mild condition. These calculations support that Au(I)‐catalyzed Conia‐ene reactions of β‐ketoesters with alkynes go through the pathway 2 proposed by Toste. 相似文献
20.
Furan‐Based o‐Quinodimethanes by Gold‐Catalyzed Dehydrogenative Heterocyclization of 2‐(1‐Alkynyl)‐2‐alken‐1‐ones: A Modular Entry to 2,3‐Furan‐Fused Carbocycles 下载免费PDF全文
Liejin Zhou Mingrui Zhang Dr. Wenbo Li Prof. Dr. Junliang Zhang 《Angewandte Chemie (International ed. in English)》2014,53(25):6542-6545
A strategy for in situ generation of furan‐based ortho‐quinodimethanes (o‐QDMs) by the gold(I)‐mediated dehydrogenative heterocyclization of 2‐(1‐alkynyl)‐2‐alken‐1‐ones in the presence of pyridine N‐oxide under mild reaction conditions was developed. These in situ furan‐based o‐QDMs were trapped by electron‐deficient olefins and alkynes, thus furnishing various 2,3‐furan‐fused carbocycles in good yields with high diastereo‐ and regioselectivities. 相似文献