- Photochamical Fragmentation of 4-Alkylpyrimidines and 2-Alkylquinolines
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Hydrogen abstraction and fragmentation occur on acetone-sensitized photolysis of 4-alkylpyrimidines 1a-c with formation of 4-methylpyrimidine (2); the selectivity for primary, secondary, and tertiary hydrogen transfer is considerably greater in 1a-c than in 2-alkylquinolines 7a-c.
- Prathapan, Sreedharan,Loft, Sarah,Agosta, William C.
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- Solvent Polarity Predictably Tunes Spin Crossover T1/2 in Isomeric Iron(II) Pyrimidine Triazoles
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Two isomeric pyrimidine-based Rdpt-type triazole ligands were made: 4-(4-methylphenyl)-3-(2-pyrimidyl)-5-phenyl-4H-1,2,4-triazole (L2pyrimidine) and 4-(4-methylphenyl)-3-(4-pyrimidyl)-5-phenyl-4H-1,2,4-triazole (L4pyrimidine). When reacted with [FeII(pyridine)4(NCE)2], where E = S, Se, or BH3, two families of mononuclear iron(II) complexes are obtained, including six solvatomorphs, giving a total of 12 compounds: [FeII(L2pyrimidine)2(NCS)2] (1), [FeII(L2pyrimidine)2(NCSe)2] (2), 2·1.5H2O, [FeII(L2pyrimidine)2(NCBH3)2]·2CHCl3 (3·2CHCl3), 3 and 3·2H2O, [FeII(L4pyrimidine)2(NCS)2] (4), 4·H2O, [FeII(L4pyrimidine)2(NCSe)2] (5), 5·2CH3OH, 5·1.5H2O, and [FeII(L4pyrimidine)2(NCBH3)2]·2.5H2O (6·2.5H2O). Single-crystal X-ray diffraction reveals that the N6-coordinated iron(II) centers in 1, 2, 3·2CHCl3, 4, 5, and 5·2CH3OH have two bidentate triazole ligands equatorially bound and two axial NCE co-ligands trans-coordinated. All structures are high spin (HS) at 100 K, except 3·2CHCl3, which is low spin (LS). Solid-state magnetic measurements show that only 3·2CHCl3 (T1/2 above 400 K) and 5·1.5H2O (T1/2 = 110 K) undergo spin crossover (SCO); the others remain HS at 300-50 K. When 3·2CHCl3 is heated at 400 K it desorbs CHCl3 becoming 3, which remains HS at 400-50 K. UV-Vis studies in CH2Cl2, CHCl3, (CH3)2CO, CH3CN, and CH3NO2 solutions for the BH3 analogues 3 and 6 led to a 6:1 ratio of Lnpyrimidine/Fe(II) being employed for the solution studies. These revealed SCO activity in all five solvents, with T1/2 values for the 2-pyrimidine complex (247-396 K) that were consistently higher than for the 4-pyrimidine complex (216-367 K), regardless of solvent choice, consistent with the 2-pyrimidine ring providing a stronger ligand field than the 4-pyrimidine ring. Strong correlations of solvent polarity index with the T1/2 values in those solvents are observed for each complex, enabling predictable T1/2 tuning by up to 150 K. While this correlation is tantalizing, here it may also be reflecting solvent-dependent speciation - so future tests of this concept should employ more stable complexes. Differences between solid-state (ligand field; crystal packing; solvent content) and solution (ligand field; solvation; speciation) effects on SCO are highlighted.
- Rodríguez-Jiménez, Santiago,Barltrop, Alexis S.,White, Nicholas G.,Feltham, Humphrey L. C.,Brooker, Sally
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p. 6266 - 6282
(2018/06/14)
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- Electron-deficient heteroarenium salts: An organocatalytic tool for activation of hydrogen peroxide in oxidations
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A series of monosubstituted pyrimidinium and pyrazinium triflates and 3,5-disubstituted pyridinium triflates were prepared and tested as simple catalysts of oxidations with hydrogen peroxide, using sulfoxidation as a model reaction. Their catalytic efficiency strongly depends on the type of substituent and is remarkable for derivatives with an electron-withdrawing group, showing reactivity comparable to that of flavinium salts which are the prominent organocatalysts for oxygenations. Because of their high stability and good accessibility, 4-(trifluoromethyl)pyrimidinium and 3,5-dinitropyridinium triflates are the catalysts of choice and were shown to catalyze oxidation of aliphatic and aromatic sulfides to sulfoxides, giving quantitative conversions, high preparative yields and excellent chemoselectivity. The high efficiency of electron-poor heteroarenium salts is rationalized by their ability to readily form adducts with nucleophiles, as documented by low pKR+ values (pKR+ red > -0.5 V). Hydrogen peroxide adducts formed in situ during catalytic oxidation act as substrate oxidizing agents. The Gibbs free energies of oxygen transfer from these heterocyclic hydroperoxides to thioanisole, obtained by calculations at the B3LYP/6-311++g(d,p) level, showed that they are much stronger oxidizing agents than alkyl hydroperoxides and in some cases are almost comparable to derivatives of flavin hydroperoxide acting as oxidizing agents in monooxygenases.
- ?turala, Ji?í,Bohá?ová, Soňa,Chudoba, Josef,Metelková, Radka,Cibulka, Radek
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p. 2676 - 2699
(2015/03/18)
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- Process for the preparation of 4-alkyl pyrimidines
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Das vorliegende Verfahren beschreibt die Synthese von 4-Alkylpyrimidinen, insbesondere 4-Methylpyrimidin. Das Verfahren l??t sich gut im technischen Ma?stab anwenden und kommt ohne den Zusatz von Wasser oder Ammoniumchlorid als Katalysator aus und erlaubt die Herstellung der gewünschten Verbindungen in guten Ausbeuten und ausgezeichneten Reinheiten ohne zeitaufwendige Extraktionsschritte.Pyrimidine dienen als Intermediate zur Synthese von bioaktiven Wirkstoffen.
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- Photochemical hydrogen abstraction by singlet and triplet nπ* states of aromatic nitrogen: Fragmentation of 4-alkylpyrimidines and 2-alkylquinolines
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On either direct irradiation in water or triplet-sensitized irradiation in acetone, pyrimidines 1a-c undergo hydrogen abstraction from an nπ* triplet state, fragmentation, and rearomatization to form 5 (eq 1). Similarly, direct irradiation of quinolines 2a-c in benzene or tert-butyl alcohol furnishes 6 from an nπ* singlet state. Quantum yields for products (Φ5 and Φ6) and Stern-Volmer quenching studies on these reactions (Tables I and II) provide mechanistic information concerning abstraction by aromatic nitrogen. Unlike Φ for abstraction by carbonyl triplets, Φ5 and Φ6 do not increase in hydrogen-bonding solvent, and there is little rate difference in transferring primary, secondary, and tertiary hydrogen in the initial step. Singlet and triplet abstractions show little difference in selectivity, but the singlet reaction is ? 104 faster. Concentration studies show that fragmentation of 1a-c is self-quenched, while reaction of 2a-c is enhanced with increasing concentration.
- Prathapan, Sreedharan,Loft, Sarah,Agosta, William C.
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p. 3940 - 3944
(2007/10/02)
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- POLAR EFFECTS IN THE HOMOLYTIC METHYLATION OF PYRIMIDINE: ORIENTATION AND POLYSUBSTITUTION
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The homolytic methylation of pyrimidine in aqueous solution has been investigated with three different radical sources: tBuOOH-Fe(2+), MeCO2H-S2O8(2-)-Ag(1+), and MeSOMe-H2O2-Fe(2+).This last reagent, used for the first time in homolytic aromatic substitution, turned out to be the most efficient.The orientation of mono- and poly-methylated derivatives is discussed on the basis of polar effects.
- Giordano, Claudio,Minisci, Francesco,Tortelli, Vito,Vismara, Elena
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p. 293 - 296
(2007/10/02)
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- Pharmaceutical compositions and methods of inhibiting gastric acid secretion
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Pharmaceutical compositions and methods of inhibiting gastric acid secretion by administering N-alkenyl and N-alkynyl thioamides.
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