Convergent Asymmetric Disproportionation Reactions: Metal/Brønsted Acid Relay Catalysis for Enantioselective Reduction of Quinoxalines

Chen, Qing‐An; Wang, Duo‐Sheng; Zhou, Yong‐Gui; Duan, Ying; Fan, Hongjun; Yang, Yan; Zhang, Zhang

doi:10.1021/ja200723n

Cited by 201 publications

(59 citation statements)

References 70 publications

(10 reference statements)

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“…The hydrogenation was performed at 28 8C under H 2 (600 psi) for 20-24 h. After carefully releasing the hydrogen, saturated sodium carbonate was added and the mixture was stirred for 15-30 min. The organic layer was separated and extracted with CH 2 Cl 2 twice, and the combined organic extracts were dried over Na 2 SO 4 and concentrated in vacuo. Purification was performed on a silica gel column eluted with hexane/EtOAc (10:1) to give the desired product.…”

Section: Methodsmentioning

confidence: 99%

Iridium‐Catalyzed Asymmetric Hydrogenation of Pyridinium Salts

Chen

et al. 2012

Angewandte Chemie

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As one of the most straightforward and powerful approaches for the preparation of optically active compounds, asymmetric hydrogenation has been successfully used for different types of aromatic compounds, including quinolines, isoquinolines, quinoxalines, indoles, pyrroles, furans, imidazoles, and aromatic carbocyclic ring, with excellent enantioselectivities. [1][2][3][4][5][6][7][8][9] Despite these advances, direct hydrogenation of simple pyridines is still a challenge. The inherent problems are apparent: First, substrates and corresponding products that possess strong coordination ability might cause the deactivation of catalysts. Second, pyridines have a stabilizing aromatic structure that might impede the reduction. Therefore, only limited examples of hydrogenation of specific pyridine derivatives bearing powerful electron-withdrawing substituent at the 2-or 3-position have been previously described. In 2000, Studer et al. reported the first homogeneous rhodium-catalyzed asymmetric hydrogenation of pyridines, but only poor enantioselectivity was obtained. [10] Zhang and co-workers described an efficient three-step rhodium-catalyzed asymmetric hydrogenation of nicotinates.[11] Subsequently, the group of Rueping documented the first enantioselective organocatalytic transfer hydrogenation of 3-cyano-or carbonyl-substituted pyridines using Hantzsch esters as hydrogen sources, [12] and our group also employed [{Ir(cod)Cl} 2 ]/(S)-MeO-biphep/I 2 catalyst system for asymmetric hydrogenation of specific pyridines with excellent enantioselectivities.[13] Additionally, an elegant asymmetric hydrogenation of activated pyridines, that is, N-iminopyridinium ylides, was developed by Charette et al. [14] As chiral piperidines are important building blocks for the synthesis of biologically active molecules and natural products, [15] the development of an efficient strategy for the highly challenging hydrogenation of the simple pyridines is still of great significance.Iminium salts generally exhibit higher activity than the corresponding imines in hydrogenation, [15b-l, 16] therefore we envisioned that the activation of simple pyridines as the corresponding N-benzyl-pyridinium bromides would effectively eliminate coordination ability of the substrate and thus the reactivity could be greatly enhanced. Moreover, the stoichiometric amount of hydrogen bromide generated in situ would effectively inhibit the coordination ability of the desired product through the formation of its piperidine hydrogen bromide salt (Scheme 1). Also, the benzyl protecting groups could be conveniently removed by hydrogenolysis. Herein, we disclose the iridium-catalyzed asymmetric hydrogenation of 2-substituted pyridinium salts with excellent enantioselectivity.Our investigation started with the asymmetric hydrogenation of N-benzyl-2-phenylpyridinium bromide using [{Ir(cod)Cl} 2 ]/(R)-MeO-biphep as the catalyst (Table 1). To our delight, when CH 2 Cl 2 was employed as the solvent, the reaction proceeded smoothly to give the target product in 84 % y...

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Section: Methodsmentioning

confidence: 99%

Iridium‐Catalyzed Asymmetric Hydrogenation of Pyridinium Salts

Chen

et al. 2012

Angewandte Chemie

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“…been achieved for the hydrogenation of quinolines [5][6][7][8][9], quinoxalines [10][11][12][13][14], pyridines [15][16][17], furans, and benzofurans [18,19]. Meanwhile, we have also directed our attention to the asymmetric hydrogenation of arenes, particularly nitrogen-containing 5-membered heteroaromatics [3].…”

Section: Open Accessmentioning

confidence: 99%

Catalytic Asymmetric Hydrogenation of 3-Substituted Benzisoxazoles

Ikeda

Kuwano

2012

Molecules

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A variety of 3-substituted benzisoxazoles were reduced with hydrogen using the chiral ruthenium catalyst, {RuCl(p-cymene)[(R,R)-(S,S)-PhTRAP]}Cl. The ruthenium-catalyzed hydrogenation proceeded in high yield in the presence of an acylating agent, affording -substituted o-hydroxybenzylamines with up to 57% ee. In the catalytic transformation, the N-O bond of the benzisoxazole substrate is reductively cleaved by the ruthenium complex under the hydrogenation conditions. The C-N double bond of the resulting imine is saturated stereoselectively through the PhTRAP-ruthenium catalysis. The hydrogenation produces chiral primary amines, which may work as catalytic poisons, however, the amino group of the hydrogenation product is rapidly acylated when the reaction is conducted in the presence of an appropriate acylating agent, such as Boc 2 O or Cbz-OSu.

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“…9 Recently many successful cases have been reported. Several approaches had been developed to benzoxazine derivatives with Mo/Fe/Al/Cr, 12 AlCl3, 13 CuI, 14 pyridinium chlorochromate, 15 [Ir(COD)Cl]2 with (S)-Segphos, 16 HSiCl3, 17 or 1,10-phenanthroline 18 as catalysts. Several approaches had been developed to benzoxazine derivatives with Mo/Fe/Al/Cr, 12 AlCl3, 13 CuI, 14 pyridinium chlorochromate, 15 [Ir(COD)Cl]2 with (S)-Segphos, 16 HSiCl3, 17 or 1,10-phenanthroline 18 as catalysts.…”

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confidence: 99%

Synthesis and Safener Activity of Novel Substituted 4-Phenoxyacetyl-1,4-benzoxazines

Shuang¹,

Ye²,

Fu³

et al. 2015

HETEROCYCLES

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A novel class of 3-methyl-4-phenoxyacetyl-3,4-dihydro-2H-1,4benzoxazine 3 were synthesized via reduction, cyclization, and acylation reactions.The structures of the compounds were characterized by IR, 1 H-NMR, 13 C-NMR, MS, and elemental analyses. The configuration of 3f was determined by X-ray crystallography. The bioassay results demonstrated that most of these compounds could alleviate 2,4-D butylate injury to maize.1,4-Benzoxazine derivatives have received great attention in chemical and medicinal research because of their natural occurrence and important biological activities. 1 Several 3,4-dihydro-2H-1,4-benzoxazine derivatives have been reported as potassium channel openers (PCOs) in vascular smooth muscle. Some 1,4-benzoxazine derivatives are known to be central nervous system depressants, antibacterial agents, 2 antipsychotic agents, 3 calcium antagonists, 4 and antimicrobial agents agonists, 5 and so on. In particular, benzoxazine derivatives with particular biological activities were applied widely in the agrochemicals fields, including herbicide safener benoxacor. 6 Structure-activity correlations (SAR) are very important in the search for biological activity because they provide useful information about chemical substituents that are necessary for the required bioactivity. 7Base on the SAR, fenoxaprop-ethyl was used as the target herbicide, and replacing the pyrazoline core from mefenpyr-diethyl by a similar substituted isoxazoline resulted in the safener 5-phenyl-4,5-dihydroisoxazole-3-carboxylic acid ethyl ester, which were not sufficiently active for commercialization. However, combining the structural features of 5-phenyl-4,5-dihydroisoxazole-3carboxylic acid ethyl ester and the safener diphenyl acid led to the strong rice safener isoxadifen-ethyl (Scheme 1). 8 Using strategies of active substructure combination and bioisosteric replacement, Guan et al.

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Convergent Asymmetric Disproportionation Reactions: Metal/Brønsted Acid Relay Catalysis for Enantioselective Reduction of Quinoxalines

Cited by 201 publications

References 70 publications

Iridium‐Catalyzed Asymmetric Hydrogenation of Pyridinium Salts

Iridium‐Catalyzed Asymmetric Hydrogenation of Pyridinium Salts

Catalytic Asymmetric Hydrogenation of 3-Substituted Benzisoxazoles

Synthesis and Safener Activity of Novel Substituted 4-Phenoxyacetyl-1,4-benzoxazines

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