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1.
Chunlan Song Kun Liu Xu Jiang Xin Dong Yue Weng Chien‐Wei Chiang Aiwen Lei 《Angewandte Chemie (International ed. in English)》2020,59(18):7193-7197
Dearomative annulation of indoles has emerged as a powerful tool for the preparation of polycyclic indoline‐based alkaloids. Compared with well‐established methods towards five‐membered‐ring‐fused indolines, the six‐membered‐ring‐fused indolines are rarely accessed under thermal conditions. Herein, a dearomative [4+2] annulation between different indoles is developed through an electrochemical pathway. This transformation offers a remarkably regio‐ and stereoselective route to highly functionalized pyrimido[5,4‐b]indoles under oxidant‐ and metal‐free conditions. Notably, this electrochemical approach maintains excellent functional‐group tolerance and can be extended as a modification tactic for pharmaceutical research. Preliminary mechanism studies indicate that the electrooxidation annulation proceeds through radical–radical cross‐coupling between an indole radical cation and an N‐centered radical generated in situ. 相似文献
2.
Cyclobutanones underwent a formal [4 + 2 + 2] annulation reaction with 1,6- and 1,7-diynes in the presence of nickel(0) catalysts to provide bicyclic eight-membered ring ketones. The annulation reaction proceeds through a ring-expansion of oxanickelacycloheptadiene via beta-carbon elimination to form a nine-membered nickelacycle. This reaction employing cyclobutanones as a C4 unit constructs cyclooctadienone cores in one synthetic step. 相似文献
3.
Gold‐Catalyzed Regiospecific C−H Annulation of o‐Ethynylbiaryls with Anthranils: π‐Extension by Ring‐Expansion En Route to N‐Doped PAHs
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Zhongyi Zeng Hongming Jin Dr. Kohei Sekine Dr. Matthias Rudolph Frank Rominger Prof. Dr. A. Stephen K. Hashmi 《Angewandte Chemie (International ed. in English)》2018,57(23):6935-6939
We describe a novel, short, and flexible approach to diverse N‐doped polycyclic aromatic hydrocarbons (PAHs) through gold‐catalyzed π‐extension of anthranils with o‐ethynylbiaryls as reagents. This strategy uses easily accessible starting materials, is simple due to high step and atom economy, and shows good functional‐group compatibility as well as scale‐up potential. Mechanistically, the tandem reaction is proposed to involve a nucleophilic addition/ring opening/regiospecific C?H annulation/protodeauration sequence terminated by a Friedel–Crafts‐type cyclization. Photophysical studies of the products indicated violet‐blue fluorescence emission with quantum yields up to 0.45. 相似文献
4.
Dr. Joseph Benford-Ward Dr. Sanaz Ahmadipour Dr. Aliya Sembayeva Dr. Louise Male Dr. Richard S. Grainger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(71):e202202429
The dolabellane-type diterpene dictyoxetane represents a significant challenge to synthetic organic chemistry. Methodology directed towards the total synthesis of naturally occurring (+)-dictyoxetane is reported. Catalytic asymmetric synthesis of the trans-hydrindane ring system is achieved through chemoselective deoxygenation of the Hajos-Parrish ketone. An alternative to the Garst-Spencer furan annulation is developed for the synthesis of a 2,5-dimethyl, tetrasubstituted furan, employing a tandem 5-exo-dig alcohol to alkyne cyclisation/aromatisation reaction as a key step. The (4+3) cycloaddition reaction of an oxyallyl cation with a tetrasubstituted furan is established on a cyclohexanone-derived model system, and a range of related (4+3) cycloadditions investigated on a homochiral, trans-hydrindane-fused furan, where regio- and diastereoselectivity is required for the natural product synthesis. In an alternative (4+2) Diels-Alder approach, a C2-symmetric vinyl sulfoxide-based chiral ketene equivalent is used to prepare oxanorbornenes with the same oxygen bridge stereochemistry found in the 2,7-dioxatricyclo[4.2.1.03,8]nonane ring system of the natural product. 相似文献
5.
[reaction: see text] A two-step electrochemical annulation has been developed for the preparation of fused furans. The process involves an initial conjugate addition of a furyethyl cuprate and trapping of the enolate as the corresponding silyl enolether. The second step of the annulation involves the anodic coupling of the furan and the silyl enol ether to form a six-membered ring. 相似文献
6.
The synthesis of several 3,5,7-trisubstituted pyrazolo[3,4-e][1,3]oxazines by ring annulation of the appropriately substituted pyrazoles is described. 相似文献
7.
An improved clean methodology has been developed for the synthesis of pyrido[2,3‐d]pyrimidin‐4‐ones through a simple one‐pot reaction of chalcones, ketones, and ammonium acetates via a [3+2+1] ring annulation. This dry media methodology, where the three components absorbed over solid inorganic support under microwave irradiation, afforded the desired product in a short reaction time. 相似文献
8.
The efficient construction of functionalized polycyclic structures is an important objective in organic synthesis. Herein, we disclose a three‐step “[2 + n]” annulation method for the transformation of cyclic ketones to fused enimines and enones. The method relies on the Suzuki coupling reaction and the amide reductive alkenylation reaction. A series of fused bicyclic (6/6, 6/7, 8/7) and tricyclic (6/6/6; 6/6/7, 6/5/7) ring systems bearing an α,β‐enimine or an α,β‐enone functionality have been synthetized in good overall yields. 相似文献
9.
Ya-Kui Sun Jin-Bao Qiao Yu-Meng Xin Qin Zhou Zhi-Hua Ma Hui Shao Yu-Ming Zhao 《Angewandte Chemie (International ed. in English)》2023,62(40):e202310917
Herein, we report a concise and divergent synthesis of the complex hasubanan alkaloids metaphanine and oxoepistephamiersine from commercially available and inexpensive cyclohexanedione monoethylene acetal. Our synthesis features a palladium-catalyzed cascade cyclization reaction to set the tricyclic carbon framework of the desired molecules, a regioselective Baeyer–Villiger oxidation followed by a MeNH2 triggered skeletal reorganization cascade to construct the benzannulated aza[4.4.3]propellane, and a strategically late-stage regio-/diastereoselective oxidative annulation of sp3 C−H bond to form the challenging THF ring system and hemiketal moiety in a single step. In addition, a highly enantioselective alkylation of cyclohexanedione monoethylene acetal paved the way for the asymmetric synthesis of target molecular. 相似文献
10.
R. Ian Fryer Rudolph F. Lauer Eugene J. Trybulski Stephen Vitone Armin Walser Gladys Zenchoff 《Journal of heterocyclic chemistry》1983,20(6):1605-1608
A facile synthesis of the 4H-imidazo[5,1-c][1,4]benzothiazine ring system is described. The synthesis utilized the annulation of an imidazole ring onto a 2H-1,4-benzothiazin-3(4H)-one via the addition of the anion of ethyl isocyanoacetate. Methods for the functionalization of the 1-, 3-, 4-, and 5-positions of the ring system are presented. 相似文献
11.
Gaponenko N. I. Kolodina A. A. Lesin A. V. Kurbatov S. V. Starikova Z. A. Nelyubina Yu. V. 《Russian Chemical Bulletin》2010,59(4):838-844
A method for annulation of the tetrahydrothiadiazine ring to benzimidazoles and 1,2,4-tri-azoles was developed. A number of
earlier unknown [1,3,4]thiadiazino[3,2-a]benzimidazoles and triazolo[3,4-b][1,3,4]thiadiazines were obtained as spiro compounds with the oxindole fragment. According to NMR and X-ray diffraction data,
the formation of the tetrahydrothiadiazine ring is a diastereospecific process. 相似文献
12.
The fragmentation patterns of the title compounds are shown to depend on the nature of the ring annulation. On ionization the cis-annulated isomers lose a molecule of benzene in contrast to the corresponding trans isomers which do not. A mechanism involving a participation of the π-electron system in the cleavage of the 5-membered ring is suggested to explain the observed differences. 相似文献
13.
Sabine Seifert Dr. David Schmidt Dr. Kazutaka Shoyama Prof. Dr. Frank Würthner 《Angewandte Chemie (International ed. in English)》2017,56(26):7595-7600
Palladium-catalyzed base-selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki–Miyaura cross-coupling and direct C−H arylation afforded a series of new five- and six-membered ring annulated electron-poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs2CO3) as auxiliary base in these C−C coupling cascade reactions led exclusively to six-membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five-membered ring annulated products. This base-dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X-ray analysis of the respective five- and six-membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry. 相似文献
14.
Long Zhao Ralf I. Kaiser Wenchao Lu Musahid Ahmed Mikhail M. Evseev Eugene K. Bashkirov Valeriy N. Azyazov Christina Tönshoff Florian Reicherter Holger F. Bettinger Alexander M. Mebel 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(28):11430-11434
A representative, low-temperature gas-phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C22H14) along with its benzo[a]tetracene isomer (C22H14) is unraveled by probing the elementary reaction of the 2-tetracenyl radical (C18H11.) with vinylacetylene (C4H4). The pathway to pentacene—a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes—is facilitated by a barrierless, vinylacetylene mediated gas-phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low-temperature pathway can launch isomer-selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free-radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe. 相似文献
15.
《Tetrahedron letters》1987,28(44):5275-5278
The construction through an A-ring annulation strategy of a fully B-ring methylated saturated tricyclic taxane model and the demonstration of its preference for trans BC ring junction stereochemistry are described. 相似文献
16.
Dr. Jiaqiong Sun Weiliang Yuan Rong Tian Peiyuan Wang Dr. Xue-Peng Zhang Prof. Xingwei Li 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(50):22895-22902
We report chiral RhIII cyclopentadienyl-catalyzed enantioselective synthesis of lactams and isochromenes through oxidative [4+1] and [5+1] annulation, respectively, between arenes and 1,3-enynes. The reaction proceeds through a C−H activation, alkenyl-to-allyl rearrangement, and a nucleophilic cyclization cascade. The mechanisms of the [4+1] annulations were elucidated by a combination of experimental and computational methods. DFT studies indicated that, following the C−H activation and alkyne insertion, a RhIII alkenyl intermediate undergoes δ-hydrogen elimination of the allylic C−H via a six-membered ring transition state to produce a RhIII enallene hydride intermediate. Subsequent hydride insertion and allyl rearrangement affords several rhodium(III) allyl intermediates, and a rare RhIII η4 ene-allyl species with π-agostic interaction undergoes SN2′-type external attack by the nitrogen nucleophile, instead of C−N reductive elimination, as the stereodetermining step. 相似文献
17.
Skeletal Rearrangement in the ZnII‐Catalyzed [4+2]‐Annulation of Disubstituted N‐Hydroxy Allenylamines with Nitrosoarenes to Yield Substituted 1,2‐Oxazinan‐3‐one Derivatives
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Pankaj Sharma Prof. Dr. Rai‐Shung Liu 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15881-15887
This work reports zinc‐catalyzed [4+2]‐annulation reactions of disubstituted N‐hydroxy allenylamines with nitrosoarenes to afford substituted 1,2‐oxazinan‐3‐ones with a skeletal rearrangement. This annulation is applicable to a reasonable scope of allenylamines and nitrosoarenes. Our control experiments indicate that nitrosobenzene can also implement this annulation through a radical annulation path, but with poor efficiency. Zn(OTf)2 or AgOTf greatly improves the efficiency of this [4+2]‐annulation; the effect of these metal species is discussed in detail. 相似文献
18.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(26):7703-7708
Palladium‐catalyzed base‐selective annulation of dibromonaphthalimide to different aryl boronate esters by combined Suzuki–Miyaura cross‐coupling and direct C−H arylation afforded a series of new five‐ and six‐membered ring annulated electron‐poor polycyclic aromatic hydrocarbons. Cesium carbonate (Cs2CO3) as auxiliary base in these C−C coupling cascade reactions led exclusively to six‐membered ring annulation, while the use of organic base diazabicycloundecene (DBU) afforded the corresponding five‐membered ring annulated products. This base‐dependent selective mode of annulation is attributed to different mechanistic pathways directed by the applied base. The selective annulation was revealed by single crystal X‐ray analysis of the respective five‐ and six‐membered ring annulated products. The optical and redox properties of the new polycyclic aromatic dicarboximides were characterized by UV/Vis absorption and fluorescence spectroscopy and cyclic voltammetry. 相似文献
19.
Long Zhao Ralf I. Kaiser Wenchao Lu Musahid Ahmed Mikhail M. Evseev Eugene K. Bashkirov Valeriy N. Azyazov Christina Tnshoff Florian Reicherter Holger F. Bettinger Alexander M. Mebel 《Angewandte Chemie (International ed. in English)》2020,59(28):11334-11338
A representative, low‐temperature gas‐phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C22H14) along with its benzo[a]tetracene isomer (C22H14) is unraveled by probing the elementary reaction of the 2‐tetracenyl radical (C18H11.) with vinylacetylene (C4H4). The pathway to pentacene—a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes—is facilitated by a barrierless, vinylacetylene mediated gas‐phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low‐temperature pathway can launch isomer‐selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free‐radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe. 相似文献
20.
Prof. Dr. Yoshihiko Yamamoto Jiyue Jiang Dr. Takeshi Yasui 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3749-3757
The palladium-catalyzed reaction of 4-iodo-2-quinolones with activated alkynes was investigated. Cyclopenta[de]quinoline-2(1 H)-ones and/or phenanthridine-6(5 H)-ones were obtained through [3+2] annulation involving aromatic C−H activation or [2+2+2] annulation involving vinylic C−H activation, respectively. Reasonable mechanisms for the formation of these annulation products have been proposed based on density functional theory calculations. 相似文献