- Synthesis of 3-Methyleneisoindolin-1-ones and Isoquinolinium Salts via Exo and Endo Selective Cyclization of 2-(1-Alkynyl)benzaldimines
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Coinage metal-promoted 5-exo and 6-endo selective cyclization of 2-(1-alkynyl)benzaldimines has been studied. It was found that, under gold catalysis, 2-(1-alkynyl)benzaldimines exclusively underwent 5-exo-dig cyclization processes, followed by oxidation to form N-aryl 3-methyleneisoindolin-1-ones. In contrast, in the presence of base and under activation of AgOTf, switching of 5-exo to 6-endo cyclizations of 2-(1-alkynyl)benzaldimines was observed, exclusively giving N-aryl or N-alkyl substituted isoquinolinium salts. The two key reaction intermediates, exocyclic vinyl-Au and the endocyclic vinyl-Ag species have been isolated and characterized, and a study of their reactivities confirms the plausible mechanisms. Reactions of the resultant 3-methyleneisoindolin-1-ones with benzyne afforded structurally important isoindolinone-based benzocyclobutenes. Additionally, several interesting transformations of the resultant isoquinolinium salts have been investigated.
- Wang, Jiwei,Xie, Congyun,Cheng, Xiang,Liu, Ye,Zhang, Jun
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- Light-driven selective aerobic oxidation of (iso)quinoliniums and related heterocycles
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Selective C1-H/C4-H carbonylation of N-methylene iminium salts, catalyzed by visible-light photoredox and oxygen in the air, has been reported. A ruthenium complex acts as a chemical switch to conduct two different reaction pathways and to afford two diff
- Zhou, Meimei,Yu, Keyang,Liu, Jianxin,Shi, Weimei,Pan, Yingming,Tang, Haitao,Peng, Xiangjun,Liu, Qian,Wang, Hengshan
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p. 16246 - 16251
(2021/05/19)
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- Co(iii)-catalysed regioselective linear C(8)-H olefination of isoquinolone with terminal aromatic and aliphatic alkynes
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A regioselective C8 linear olefination of isoquinoline-1H-2-one with terminal (aromatic and aliphatic) alkynes is reported under Co(iii) catalysis. This is an exclusive report on the C8 functionalization of isoquinolone using non-noble transition metal co
- Chandra, Devesh,Gupta, Puneet,Kumar, Nikunj,Parmar, Diksha,Sharma, Upendra,Sumit
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p. 11613 - 11616
(2021/11/12)
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- Covalent Organic Frameworks toward Diverse Photocatalytic Aerobic Oxidations
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Photoactive two-dimensional covalent organic frameworks (2D-COFs) have become promising heterogenous photocatalysts in visible-light-driven organic transformations. Herein, a visible-light-driven selective aerobic oxidation of various small organic molecules by using 2D-COFs as the photocatalyst was developed. In this protocol, due to the remarkable photocatalytic capability of hydrazone-based 2D-COF-1 on molecular oxygen activation, a wide range of amides, quinolones, heterocyclic compounds, and sulfoxides were obtained with high efficiency and excellent functional group tolerance under very mild reaction conditions. Furthermore, benefiting from the inherent advantage of heterogenous photocatalysis, prominent sustainability and easy photocatalyst recyclability, a drug molecule (modafinil) and an oxidized mustard gas simulant (2-chloroethyl ethyl sulfoxide) were selectively and easily obtained in scale-up reactions. Mechanistic investigations were conducted using radical quenching experiments and in situ ESR spectroscopy, all corroborating the proposed role of 2D-COF-1 in photocatalytic cycle.
- Liu, Shuyang,Tian, Miao,Bu, Xiubin,Tian, Hua,Yang, Xiaobo
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p. 7738 - 7744
(2021/05/07)
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- Oxidation of the inert sp3C-H bonds of tetrahydroisoquinolines through C-H activation relay (CHAR): construction of functionalized isoquinolin-1-ones
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A TBN/O2-initiated oxidation of the relatively inert 3,4-C-H bonds of THIQs was accomplished, in which the existence of an α-phosphoric ester group is crucial to enable dioxygen trapping and intramolecular HAT (C-H activation relay,CHAR), reali
- Yuan, Yuan,Zhang, Shuwei,Sun, Zheng,Su, Yichun,Ma, Qiyuan,Yuan, Yu,Jia, Xiaodong
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supporting information
p. 3347 - 3350
(2021/04/07)
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- Visible-Light-Induced Controlled Oxidation of N-Substituted 1,2,3,4-Tetrahydroisoquinolines for the Synthesis of 3,4-Dihydroisoquinolin-1(2H)-ones and Isoquinolin-1(2H)-ones
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A visible light-rose bengal-TBHP mediated, controlled oxidation of N-substituted 1,2,3,4-tetrahydroisoquinolines is developed for the synthesis of 3,4-dihydroisoquinolin-1(2H)-ones and isoquinolin-1(2H)-ones. The present method feature's a broad substrate scope, good functional group tolerances, and the products were prepared in good to excellent yields. The developed methodology further demonstrated in the synthesis of isoindolo[2,1-b] isoquinolin-5(7H)-one (topoisomerase-I inhibitor). (Figure presented.).
- Bansode, Ajay H.,Suryavanshi, Gurunath
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supporting information
p. 1390 - 1400
(2021/01/26)
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- I2-Promoted Direct C?H Sulfenylation of Isoquinolin-1(2H)-ones with Sulfonyl Chlorides
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A simple, efficient, and green method for the iodine-promoted regioselective C-4 sulfenylation of isoquinolin-1(2H)-ones using commercially available aryl sulfonyl chlorides as the sulfur source was described under metal- and solvent-free conditions. The reaction proceeded smoothly under simple conditions to obtain 4-arylthioisoquinolin-1(2H)-ones in moderate to good yields, and showed high regioselectivity, broad substrate scope, and good functional group tolerance. A radical reaction mechanism involving ArS. radicals as key intermediates is proposed for the present transformation.
- Yang, Cai-Yun,Li, Xia,Liu, Bo,Huang, Guo-Li
-
supporting information
p. 117 - 124
(2020/12/17)
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- Co(III)-Catalyzed Annulative Vinylene Transfer via C-H Activation: Three-Step Total Synthesis of 8-Oxopseudopalmatine and Oxopalmatine
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The Co(III)-catalyzed redox-neutral annulation of benzamides and acrylamides with vinylene carbonate for the synthesis of isoquinolinones and pyridinones has been developed. This protocol employing inexpensive Co(III) as the catalyst tolerated diverse functional groups and substitution patterns, affording the target products with good to excellent yields. The synthetic utility of this transformation was demonstrated by a three-step synthesis of gusanlung D, 8-oxopseudopalmatine, and oxopalmatine.
- Li, Xinghua,Huang, Ting,Song, Ying,Qi, Yue,Li, Limin,Li, Yanping,Xiao, Qi,Zhang, Yuanfei
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supporting information
p. 5925 - 5930
(2020/08/12)
-
- Base-promoted aerobic oxidation of: N -alkyl iminium salts derived from isoquinolines and related heterocycles
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Potassium tert-butoxide-promoted aerobic oxidation of N-alkyl iminium salts is reported. The reaction is atom-economical and environmentally friendly. Iminium salts derived from isoquinoline, quinoline, phenanthridine, phenanthroline, and phthalazine were successfully transformed into their corresponding unsaturated lactams with up to 95% yield under mild conditions in the absence of photocatalysts and metallic or organic catalysts. Owing to the general substrate scope, low cost, feasibility of scale up, wide availability of reagents, and green reaction conditions, this method shows great potential for preparing isoquinolones and related compounds. The method was applied for atom- and step-economical total synthesis of natural products such as norketoyobyrine.
- Bai, Li-Gang,Zhou, Yue,Zhuang, Xin,Zhang, Liang,Xue, Jian,Lin, Xiao-Long,Cai, Tian,Luo, Qun-Li
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p. 197 - 203
(2020/01/13)
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- Tandem Reaction Approaches to Isoquinolones from 2-Vinylbenzaldehydes and Anilines via Imine Formation-6π-Electrocyclization-Aerobic Oxidation Sequence
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Two distinctive transition-metal-promoted aerobic oxidation protocols have been developed for the synthesis of isoquinolones from 2-vinylbenzaldehydes and aniline derivatives. Thus, the one-pot tandem reaction sequence of imine formation, thermal 6π-electrocyclization, followed by either Cu(OAc)2-mediated or Pd(OAc)2-catalyzed aerobic oxidation protocol allowed the ready access to isoquinolone derivatives. The control experiments revealed that the 1,2-dihydroisoquinoline intermediates from the 6π-electrocyclization of 1-azatrienes were aerobically oxidized to isoquinolones in the presence of either Cu(OAc)2 or Pd(OAc)2 catalyst.
- Lee, Jiyeon,Kim, Hun Young,Oh, Kyungsoo
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p. 474 - 478
(2020/01/21)
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- Deprotonated Salicylaldehyde as Visible Light Photocatalyst
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Salicylaldehyde is established as an efficient visible light photocatalyst for the first time. Compared to other simple aldehyde analogies, salicylaldehyde has a unique deprotonative red-shift from 324 to 417 nm and gives rise to the remarkable increase of fluorescence quantum from 0.0368 to 0.4632, thus enabling salicylaldehyde as a visible light (>400 nm) photocatalyst. The experimental investigations suggest that the reactive radical species are generated by sensitization of the substrates by the deprotonated salicylaldehyde through an energy-transfer pathway. Consequently, the C-C cleaving alkylation reactions of N-hydroxyphthalimide esters proceed smoothly in the presence of as low as 1 mol % of salicylaldehyde under the visible-light irradiation, affording desired alkylation products with up to 99% yields. Application in visible-light induced aerobic oxidation of N-alkylpyridinium salts is also reported.
- Zhuang, Yan-Jun,Qu, Jian-Ping,Kang, Yan-Biao
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p. 4386 - 4397
(2020/03/05)
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- I2/TBHP mediated multiple C[sbnd]H bonds functionalization of azaarenes with methylarenes to synthesize iodoisoquinolinones via iodination/N-benzylation/amidation sequence
-
An oxidative multi-functionalization of azaarenes with benzylic C[sbnd]H bonds of methylarenes via iodination/N-benzylation/amidation cascade, to produce N-benzyl-4-iodoisoquinolin-1(2H)-ones and N-benzyl-3-iodoquinolin-2(1H)-ones is developed. The molecular iodine plays a triple role in activating benzylic sp3 C[sbnd]H bond of methylbenzenes, accelerating the oxidation process and serving as iodination reagent. This reaction utilizes cheap and readily available azaarenes and methylarenes as starting materials and proceeds under metal-free conditions to construct C-I, C[sbnd]N and C[dbnd]O bonds consecutively and afford iodo(iso)quinolinones efficiently.
- Luo, Wen-Kun,Xu, Cong-Ling,Yang, Luo
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- Efficient and rapid synthesis of N-substituted isoquinolin-1-ones under mild conditions: Facile access to doryanine derivatives
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We describe the simple and efficient synthesis of N-substituted isoquinolin-1-one derivatives. Initiating with the coupling of benzoic acids containing vinyl ethers with different amines, followed by rapid intramolecular cyclization under acidic conditions at room temperature, N-substituted isoquinolin-1-ones were furnished in high yields. The utility of this simple and mild cyclization method was demonstrated through the practical synthesis of natural product doryanine and its analogues.
- Takwale, Akshay. D.,Jeon, Yeong Uk,Lee, Dong Ho,Kim, Hyun Jin,Hwang, Jong Yeon
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p. 1259 - 1261
(2019/04/04)
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- Carbene-catalyzed aerobic oxidation of isoquinolinium salts: Efficient synthesis of isoquinolinones
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A mild and environmentally friendly carbene-catalyzed aerobic oxidation of isoquinolinium salts was successfully realized. Accordingly, a diverse set of isoquinolinones and phenanthridinones was efficiently prepared in good to excellent yields. The mechanistic study indicates that the formation of an aza-Breslow intermediate is the crucial step in this transformation. This reaction features ambient air as the sole oxidant and oxygen source, a broad substrate scope, and excellent functional-group tolerance and proceeds under mild reaction conditions. Furthermore, a highly efficient synthesis of bioactive molecules and natural products including N-methylcrinasiadine, N-isopentylcrinasiadine, N-phenethylcrinasiadine, isoindolo[2,1-b]isoquinolin-5(7H)-one, PJ-34, rac-Gusanlung D, rosettacin, 8-oxopseudopalmatine and ilicifoline B was accomplished.
- Wang, Guanjie,Hu, Wanyao,Hu, Zhouli,Zhang, Yuxia,Yao, Wei,Li, Lin,Fu, Zhenqian,Huang, Wei
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p. 3302 - 3307
(2018/07/29)
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- Iridium(III)-Catalyzed Regiocontrolled Direct Amidation of Isoquinolones and Pyridones
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Iridium(III)-catalyzed highly regiocontrolled C3/C8 amidation of isoquinolones and C6 amidation of 2-pyridones has been successfully accomplished with various azides. The optimized method is operationally simple with a broad substrate scope. The protocol has been found to be scalable. (Figure presented.).
- Das, Debapratim,Samanta, Rajarshi
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supporting information
p. 379 - 384
(2017/12/26)
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- Selectivity of N-versus O-alkylation in Mitsunobu reactions with various quinolinols and isoquinolinols
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Reacting quinolinols and isoquinolinols under Mitsunobu conditions can give rise to N-alkylated products in addition to the normally desired O-alkylated structures. An in-depth study of how the solvent, reagent equivalents, position of the quinoline/isoqu
- Hartung, Ryan E.,Wall, Mark C.,Lebreton, Sylvain,Smrcina, Martin,Patek, Marcel
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p. 1305 - 1313
(2017/07/18)
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- Visible-Light-Mediated Aerobic Oxidation of N-Alkylpyridinium Salts under Organic Photocatalysis
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Quinolones and isoquinolones exhibit diverse biological and pharmaceutical activities, and their synthesis is highly desirable under mild conditions. Here, a highly efficient and environmentally friendly visible light-mediated aerobic oxidation of readily available N-alkylpyridinium salts has been developed with Eosin Y as the organic photocatalyst and air as the terminal oxidant, and the reaction provided quinolones and isoquinolones in good yields. The method shows numerous advantages including mild and environmentally friendly conditions, high efficiency, tolerance of wide functional groups and low cost. Furthermore, 4-desoxylonimide with important pharmaceutical activities was effectively prepared by using our method. Therefore, the present method should provide a novel and useful strategy for synthesis and modification of N-heterocycles.
- Jin, Yunhe,Ou, Lunyu,Yang, Haijun,Fu, Hua
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supporting information
p. 14237 - 14243
(2017/10/17)
-
- Ruthenium-Mediated Dual Catalytic Reactions of Isoquinoline via C?H Activation and Dearomatization for Isoquinolone
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We have unraveled the ruthenium-promoted prototype reaction based on C(sp2)?C(sp3) bond formation through the reigoselective C?H activation of isoquinoline and pyridine derivatives with various alkyl halides, leading to 1-substituted isoquinoline products in good yield. This C?H catalytic reaction did not rely on chelation assistance of the directing group of the substrates. The dimer [RuCl2(p-cymene)]2in combination with an N-heterocyclic carbene ligand, adamantanecarboxylic acid and K2CO3base in N-methyl-2-pyrrolidone solution at 150 °C are the best conditions. Simultaneously, we are also able to chemically tune the reaction mode to dearomatization by adding water, leading to isoquinolone products. This reaction methodology is not suitable for other nitrogen-containing heteroarenes such as pyridazines and pyrimidines. (Figure presented.).
- Wang, Ting-Hsuan,Lee, Wei-Chih,Ong, Tiow-Gan
-
supporting information
p. 2751 - 2758
(2016/09/13)
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- Iodine-Catalyzed Oxidative Functionalization of Azaarenes with Benzylic C(sp3)-H Bonds via N-Alkylation/Amidation Cascade: Two-Step Synthesis of Isoindolo[2,1-b]isoquinolin-7(5H)-one
-
An efficient and practical iodine-catalyzed oxidative functionalization of azaarenes with benzylic C-H bonds via an N-alkylation and amidation cascade is developed to provide isoquinolin-1(2H)-ones. This method utilizes readily available unfunctionalized azaarenes and methylarenes as starting materials and proceeds under metal-free conditions with good to excellent yields, avoiding the use of expensive noble metal catalysts and generation of halide and metal wastes. The synthetic utility of this reaction is exemplified by the concise, two-step synthesis of isoindolo[2,1-b]isoquinolin-7(5H)-one.
- Luo, Wen-Kun,Shi, Xin,Zhou, Wang,Yang, Luo
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supporting information
p. 2036 - 2039
(2016/06/01)
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- Preparation method of polysubstituted 2-benzyl-1-isoquinolone compound
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The invention discloses a preparation method of a polysubstituted 2-benzyl-1 (2H)-isoquinolone compound. In the presence of an iodine catalyst and tert-butyl hydroperoxide serving as an oxidizing agent, an isoquinoline compound experiences a benzyl free r
- -
-
Paragraph 0009
(2016/10/09)
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- Copper-Mediated Oxidative Functionalization of C(sp3)-H Bonds with Isoquinolines: Two-Step Synthesis of 5-Oxaprotoberberinones
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A copper-mediated oxidative functionalization of C(sp3)-H bonds with isoquinolines via a radical process without ligands was achieved. The present system exhibits a novel pathway for the preparation of N-alkyl (benzyl) isoquinolin-1(2H)-ones in moderate to high yields. In addition, this procedure provides a simple method to afford 5-oxaprotoberberinones and their derivatives in two steps.
- Wang, Dingyi,Zhang, Rongxing,Deng, Ruihong,Lin, Sen,Guo, Shengmei,Yan, Zhaohua
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p. 11162 - 11167
(2016/11/28)
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- Expeditious Synthesis of the Topoisomerase i Inhibitors Isoindolo[2,1- b ]isoquinolin-7(5 H)-one and the Alkaloid Rosettacin Based on Aryl Radical Cyclization of Enamide Generated by Using N -Acylaiminium Chemistry
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A short and effective approach to the synthesis of the topoisomerase I inhibitor isoindolo[2,1-b]isoquinolin-7(5H)-one and the alkaloid rosettacin belonging to the aromathecin family is presented. The key step of this sequence, which resulted in the formation of a five-membered ring, was the aryl radical cyclization of enamides generated using N-acyliminium chemistry.
- El Blidi, Lahssen,Namoune, Aurélie,Bridoux, Alexandre,Nimbarte, Vijaykumar D.,Lawson, Ata Martin,Comesse, Sébastien,Da?ch, Adam
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p. 3583 - 3592
(2015/11/18)
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- INDOLE BASED RECEPTOR CRTH2 ANTAGONISTS
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Disclosed are compounds of Formula (I): which are useful as antagonists of the CRTH2 receptors. Pharmaceutical compositions containing compounds of Formula (I) and the use of compounds of Formula (I) to treat diseases or disorders that are responsive to inhibition of the binding of endogenous ligands to the CRTH2 receptor are also disclosed. Methods for preparing and using these compounds are further described.
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Page/Page column 44; 45
(2011/05/08)
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- Palladium-catalyzed annulation of haloanilines and halobenzamides using norbornadiene as an acetylene synthon: A route to functionalized indolines, isoquinolinones, and indoles
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A general procedure for the palladium-catalyzed annulation of substituted haloanilines with norbornadiene gives functionalized indolines in 51-98% yield. These indolines can be rapidly converted to benzenoid- substituted indoles and tricyclic indolines. Extension to the use of substituted halobenzamides gives functionalized isoquinolinones in up to 86% yield.
- Thansandote, Praew,Hulcoop, David G.,Langer, Michael,Lautens, Mark
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supporting information; experimental part
p. 1673 - 1678
(2009/07/17)
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- Reaction of 1-alkylthioisoquinolinium salts with active methylene compounds
-
2-Alkyl-1-alkylthioisoquinolinium salts were readily prepared from 2-alkyl-1(2H)-isoquinolones via 2-alkyl-1(2H)-thioisoquinolones in two steps. Under mild conditions, the reaction of 2-alkyl-l-alkylthioisoquinolinium salts with active methylene compounds in the presence of sodium hydride afforded 2-alkyl-1-(substituted methylene) iso-quinolines in good yields. Pyrrolo[2,1-a]isoquinolines were synthesized by the cyclization of 2-benzyl-1-(substituted methylene)isoquinolines using acetic anhydride.
- Fujita, Reiko,Watanabe, Noriyuki,Tomisawa, Hiroshi
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p. 225 - 228
(2007/10/03)
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- 5-Nitrofuran-2-ylmethyl group as a potential bioreductively activated pro-drug system
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5-Substituted isoquinolin-1-ones have been synthesised by one-pot Curtius rearrangement of the corresponding substituted 3-phenylpropenoyl azides and cyclisation. Arylmethylation of the anions of the isoquinolinones with benzyl halides [4-methoxybenzyl chloride, 2-(chloromethyl)furan and 5-nitro-2-(tosyloxymethyl)furan] takes place exclusively at nitrogen. Nitration of 2-(furan-2-ylmethyl)isoquinolin-1-one in strongly acidic medium gives 2-(5-nitrofuran-2-ylmethyl)isoquinolin-1-one, whereas weaker acidic conditions lead to dinitration. Curtius rearrangement of 3-carboranylbutanoyl azide and trapping with 5-nitrofuran-2-ylmethanol gives 5-nitrofuran-2-ylmethyl N-(3-carboranylpropyl)carbamate. Biomimetic reduction of these nitrofuranylmethyl derivatives of anticancer drugs triggers release of the parent drugs. Thus, these nitrofurans have potential applications as pro-drugs for selective release of therapeutic drugs in hypoxic solid tumours.
- Berry, Jane M.,Watson, Corrine Y.,Whish, William J. D.,Threadgill, Michael D.
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p. 1147 - 1156
(2007/10/03)
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- Synthesis of 3,4-dihydroisoquinolines, 2-alkyl(acyl)-1(2H)-3,4-dihydroisoquinolinones, 2-alkyl-1(2H)-isoquinolinones and 1-alkyl-2(2H)-quinolinones by oxidation with potassium permanganate
-
Synthesis of 3,4-dihydroisoquinolines 2, 2-alkyl- 6 and 2-acyl-3,4-dihydro-1(2H)-isoquinolinones 9, 2-alkyl-1(2H)-isoquinolinones 14, N-alkyl-3,4-dihydro-2(2H)-quinolinones 16 and N-alkyl-2(2H)-quinolinones 19 by oxidation of 1,2,3,4-tetrahydroisoquinolines 1, N-alkyl (acyl)iminium salts of 3,4-dihydroisoquinolines 5,8 and isoquinoline 13 as well as of N-alkyl ammonium salts of tetrahydroquinoline 15 and quinoline 18 with potassium permanganate is described.
- Venkov,Statkova-Abeghe
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p. 1451 - 1460
(2007/10/03)
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- Synthetic approaches to 2-substituted 1-oxo- and 3-oxotetrahydroisoquinolines
-
2-Substituted homophthalimides 2a-c were reduced regioselectively with sodium borohydride to carbinol-lactam intermediates 3a-c, which were dehydrated, followed by hydrogenation, to give 1-oxotetrahydroisoquinolines or 3,4-dihydroisoquinolin-1(2H)ones 5a-c. The isomeric 3-oxo-tetrahydroisoquinolines or 1,4-dihydroisoquinolin-3(2H)-ones 8a-i were obtained in satisfactory yields via heating 3-isochromanone (6) with the corresponding amines 7a-i in the presence of aluminum chloride.
- Cheng,Tsai,Lin
-
-
- Investigations concerning the benzylation of tetrahydroisoquinolines with benzaldehyde and substituted benzaldehyde (Rugheimer-Burrows-reaction)
-
The condensation of piperidine and tetrahydroisoquinoline derivatives with benzaldehyde leading to the corresponding benzylated aromatic systems is a multistep reaction for which different mechanisms are discussed. Isolation and characterization of the following intermediates and side products are helpful to explain parts of the sequence.
- Dannhardt,Roelcke
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p. 671 - 677
(2007/10/02)
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- Intramolecular "Diene-Regenerable" Diels-Alder Reaction of 2-Pyrone-6-carboxamides. Preparation and Reaction of Fused 1,3-Cyclohexadiene Systems
-
The 2-pyrone-6-carboxamides, prepared from 2-pyrone-6-carbonyl chloride and substituted allylamine, undergo intramolecular Diels-Alder reaction spontaneously to give 3a,4,5,7a-tetrahydro-1-oxoisoindoline-5,7a-carbolactones, which regenerate the diene moie
- Noguchi, Michihiko,Kakimoto, Shinji,Kawakami, Hisao,Kajigaeshi, Shoji
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p. 1355 - 1362
(2007/10/02)
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- Kinetics of the Oxidation of Isoquinolinium Cations by Ferricyanide Ion
-
The rates of the ferricyanide oxidation of a number of isoquinolinium cations have been investigated in the range pH 11-14 in 20percent CH3CN-80percent H2O at 25 deg C (ionic strength 1.0).The oxidation of the 2-methylisoquinolinium cation is kinetically first order in each of ferricyanide ion and isoquinolinium cation but is subject to pronounced inhibition by the ferrocyanide ion reaction product.Second-order rate constants evaluated from initial reaction rates display a pH dependence which is consistent with rate-determining ferricyanide attack on the pseudobase alkoxide ion derived from the isoquinolinium cation.Ferrocyanide ion inhibition is shown to be consistent with this initial electron transfer being a reversible process.Similar observations are made for a number of substituted isoquinolinium cations.Substituent effects are shown to be consistent with electron abstraction from the endocyclic nitrogen atom rather than the exocyclic oxyanion of these pseudobase alkoxide ions.The initially formed radical then undergoes a base-catalyzed deprotonation from C-1, and this is confirmed by deuterium kinetic isotope effects when a deuterium label is present at C-1.The combination of these pH effects leads to ferrocyanide ion inhibition becoming less pronounced with increasing pH.These observations have prompted us to reinvestigate the ferricyanide ion oxidation of some of the 5-nitroisoquinolinium cations that we have previously studied.We find that ferrocyanide ion inhibition is observable when the initial rates of these reactions are examined in the stopped-flow spectrophotometer.Detailed kinetic analysis of these oxidations is shown to be consistent with the reaction scheme detailed above for the 2-methylisoquinolinium cation.In the light of this work, we must now withdraw our earlier claim for rate-determining hydride abstraction in these reactions.Substituent effects on the oxidation of these isoquinolinium cations allow the development of a relationship which can be used to predict the pH-rate profile for the ferricyanide ion oxidation of any isoquinolinium cation for which pKR+ for pseudobase formation is available, provided that steric hindrance from the N substituent is not significant.
- Bunting, John W.,Stefanidis, Dimitrios
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p. 2060 - 2067
(2007/10/02)
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