3438-46-8Relevant articles and documents
Photochamical Fragmentation of 4-Alkylpyrimidines and 2-Alkylquinolines
Prathapan, Sreedharan,Loft, Sarah,Agosta, William C.
, p. 6853 - 6856 (1988)
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.
Electron-deficient heteroarenium salts: An organocatalytic tool for activation of hydrogen peroxide in oxidations
?turala, Ji?í,Bohá?ová, Soňa,Chudoba, Josef,Metelková, Radka,Cibulka, Radek
, p. 2676 - 2699 (2015/03/18)
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.
Photochemical hydrogen abstraction by singlet and triplet nπ* states of aromatic nitrogen: Fragmentation of 4-alkylpyrimidines and 2-alkylquinolines
Prathapan, Sreedharan,Loft, Sarah,Agosta, William C.
, p. 3940 - 3944 (2007/10/02)
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.