- Microwave-enhanced reactivity of non-activated dienophiles towards pyrazine o-quinodimethanes
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Microwave irradiation in solvent-free conditions induces cycloaddition reactions of pyrazine o-quinodimethane intermediates with electron-rich dienophiles within 10-15 min to afford quinoxaline derivatives in acceptable yields.
- Díaz-Ortiz, Angel,De la Hoz, Antonio,Moreno, Andrés,Prieto, Pilar,León, Rafael,Herrero, María A.
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- New ligands that promote cross-coupling reactions between aryl halides and unactivated arenes
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Several ligands were designed to promote transition-metal-free cross-coupling reactions of aryl halides with benzene derivatives. Among the systems probed, quinoline-1-amino-2-carboxylic acid was found to serve as an excellent catalyst for cross-coupling between aryl halides and unactivated benzene. Reactions using this inexpensive catalytic system displayed a high functional group tolerance as well as excellent chemoselectivities.
- Qiu, Yatao,Liu, Yanghan,Yang, Kai,Hong, Wenkun,Li, Zheng,Wang, Zhaoyang,Yao, Zhiyi,Jiang, Sheng
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supporting information; experimental part
p. 3556 - 3559
(2011/09/14)
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- A general synthesis of diarylketones by means of a three-component cross-coupling of aryl and heteroaryl bromides, carbon monoxide, and boronic acids
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Pd(OAc)2/di-1-adamantyl-n-butylphosphine (cataCXium A) is highly active in the three-component Suzuki carbonylation and represents the most general catalyst system reported up to now. A broad range of aryl/heteroaryl bromides and aryl boronic acids can be coupled to the corresponding diarylketones at low catalyst loadings.
- Neumann, Helfried,Brennfuehrer, Anne,Beller, Matthias
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experimental part
p. 3645 - 3652
(2009/04/11)
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- Spectral-luminescent properties of 2,3-diphenyl-6-X-quinoxalines
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A study is made of the spectral-luminescent properties of solutions of 2- and 6-phenylquinoxalines and 2,3-diphenyl-6-X-quinoxalines (X = H, CH3, OC2H5, NH2, C6H5, C6H5O, C6H5CHOH, I, Br, Cl) in a hydrocarbon and 95% ethanol at 295 and 77 K. The energies of the S1 and T1 states obtained (25 600-27 700 and 18 500-20 000 cm-1, respectively) are correlated to the nature of the substituents. The mixed character of the luminescence is inferred from the close location of the S(ππ*) and S(nπ*) levels for the majority of the compounds. The contribution from the ππ* component increases with increasing electron-donating power of the substituent, as well as in going from nonpolar to polar solvent. The quantum yields of fluorescence φ = 10-4-1.1 × 10-1, of the intercombination transition φST = 0.3-0.9, and of phosphorescence φph = 0.2-0.9, the phosphorescence lifetime (τph = 10-3-0.57 s), as well as the established phenomenon of phosphorescence of liquid solutions, are analyzed in the framework of the vibronic and spin-orbit coupling schemes and conformational changes caused by excitation. The difference in the luminescent properties of 2,3-diphenyl-6-aminoquinoxalines from its examined analogs is due to a low energy of the S1(ππ*) level (21 200 cm-1 in alcohol), which is responsible for intense fluorescence (φf -0.5 in alcohol) and very weak phosphorescence.
- Rtishchev,Dobrodei,El'tsov
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p. 1658 - 1668
(2007/10/03)
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