- A Chiral Phenanthroline Ligand with a Hydrogen-Bonding Site: Application to the Enantioselective Amination of Methylene Groups
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A silver-catalyzed amination is reported that occurs at the aliphatic C3-substituent of various quinolones and pyridones. The C-H amination reaction proceeded with high site-and enantioselectivity (14 examples, 83-97% ee). The key to its success is the use of a chiral phenanthroline ligand that is attached via an ethynyl linker to the 8-position of octahydro-1H-4,7-methanoisoindol-1-one. AgPF6 (10 mol %) served as the silver source, PhI.NNs as the nitrene precursor, and 1,10-phenanthroline as the coligand. The reaction outcome can be understood by assuming a nitrene C-H insertion within a hydrogen-bonded silver complex in which a single C-H bond is exposed to the catalytic reaction center.
- Annapureddy, Rajasekar Reddy,Jandl, Christian,Bach, Thorsten
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p. 7374 - 7378
(2020/08/06)
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- Acid-Catalyzed Regiodivergent Annulation of 4-Hydroxycoumarins with Isoprene: Entry to Pyranocoumarins and Pyranochromones
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An acid-catalyzed regiodivergent formal [3+3] annulation of 4-hydroxycoumarins with isoprene is developed. A variety of pyranocoumarins were obtained exclusively in the presence of strong Br?nsted acid, while varying to Lewis acid delivered pyranochromones as main products. The protocol also features high atom-economy, wide substrate scope, easy scale-up, and good applications in natural product synthesis.
- Li, Ying,Hu, Yan-Cheng,Zheng, Hao,Ji, Ding-Wei,Cong, Yu-Feng,Chen, Qing-An
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supporting information
p. 6510 - 6514
(2019/10/22)
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- Simple efficient synthesis of pyranoquinoline alkaloids: Flindersine, khaplofoline, haplamine and their analogues
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An efficient two step synthesis of pyranoquinoline alkaloids is described. Direct treatment of isoprene with 4-hydroxyquinolin-2(1H)-one in the presence of polyphosphoric acid furnished dihydroflindersine in good yield, and which on dehydrogenation led to a new synthesis of flindersine. Khaplofoline, a linear pyranoquinoline alkaloid, was obtained as a minor product. The syntheses of derivatives are also documented.
- Thangavel, Dhanabal,Ravindran, Sangeetha,Moonsamy, Gengan Robert,Palathurai, Mohan Subramaniam
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p. 124 - 126
(2008/02/11)
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- Synthesis of pyranoquinoline alkaloids via (4+2) cycloaddition reaction
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An easy route to synthesize pyranoquinoline based alkaloids like flindersine, haplamine, N-methylflindersine and its derivatives were performed from the respective 4-hydroxyquinolin-2(1H)-one, dimethyl acrylic acid and para formaldehyde through generation of O-quinone methide intermediates and subjecting (4+2) cycloaddition. Further, dihydro intermediates were oxidized by DDQ.
- Suresh,Dhanabal,Nandha Kumar,Mohan
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- A NEW APPROACH TO HEMITERPENOID TRICYCLIC QUINOLONES. SYNTHESIS OF N-METHYLFLINDERSINE, KHAPLOPHOLINE AND OTHER STRUCTURALLY SIMILAR ALKALOIDS
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A new and general synthesis of tricyclic quinolone alkaloids is described which, by cyclization of 3-butenyl-4-hydroxyquinolones promoted by mercury(II) ion or by formic acid, affords pyranoquinolones and pyranoquinolones, respectively, with regio- and site-selectivity better than those obtained employing known methodologies. 3-Butenyl-4-hydroxyquinolones have been reacted with mercury(II) acetate to give, after work-up, the corresponding 2-(chloromercurymethyl)pyranoquinolones, which have been reductively demercurated with sodium borohydride and then dehydrogenated by treatment with DDQ.Alternatively, from the same starting compounds the "linear" isomers are obtained by formic acid-promoted cyclization.N-Methylflindersine, khaplofoline and other structurally similar alkaloids have been obtained.
- Bravo, Pierfrancesco,Resnati, Giuseppe,Viani, Fiorenza,Cavicchio, Giancarlo
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p. 507 - 512
(2007/10/02)
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- MERCURY(II)-PROMOTED CYCLIZATION OF SOME 2-ALKENYLPHENOLS AND SOME CYCLIC 2-ALKENYL-1,3-DIKETONES, 3-KETO ESTERS, AND 3-KETO AMIDES: SYNTHESIS OF 2,3-DIHYDROFURAN, 3,4-DIHYDRO-2H-PYRAN, AND 2,3,4,5-TETRAHYDROOXEPIN RINGS FUSED ON CARBOCYCLIC OR ON OXYGEN
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Treatment of 4-hydroxy-3-(substituted 3-buten-1-yl)-2H-pyran-2-ones, 4-hydroxy-3-(substituted 3-buten-1-yl)-2(1H)-quinolinones, 2-(substituted 3-buten-1-yl)-1,3-cyclohexanediones and 2-(substituted 3-buten-1-yl)phenols with mercuric acetate in tetrahydrof
- Bravo, Pierfrancesco,Vita, Cristina De,Ticozzi, Calimero,Viani, Fiorenza,Cavicchio, Giancarlo
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p. 441 - 448
(2007/10/02)
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