- Copper-Catalyzed Regioselective Direct C–H Thiolation and Thiocyanation of Uracils
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A novel copper-catalyzed direct C–H thiolation and thiocyanation of uracils using disulfides and thiocyanate salts respectively as coupling partners are described. These reactions enable the C–H bond cleavage and C–S bond formation to proceed efficiently under relatively mild conditions, providing useful methods for a preparation of a series of thio-substituted at the C5 position of uracil derivatives. These protocols exhibit several merits including simple experimental procedures, readily accessible substrates and reagents, broad scopes, high yields, and excellent regioselectivity. Preliminary mechanistic studies revealed that a radical pathway is likely to be involved.
- Noikham, Medena,Yotphan, Sirilata
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supporting information
p. 2759 - 2766
(2019/04/08)
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- HSAB-driven chemoselective N1-alkylation of pyrimidine bases and their 4-methoxy- or 4-acetylamino-derivatives
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The lithium salts of the conjugated bases of 4-methoxy- and 4-acetylamino-2(1H)-pyrimidinones 1-3 undergo highly chemoselective N1-methylation or ethylation when treated with methyl- or ethylsulfate (hard electrophiles) in dry dioxane, while the use of DMF as solvent results in competitive O2-alkylation. Potassium salts of the same bases in DMF undergo prevalent O2-attack. Under the same conditions, a similar but less chemoselective behaviour is observed in alkylation of thymine and uracil, where some N3-attack occurs. This can be rationalised in terms of the HSAB principle.
- Gambacorta, Augusto,Tofani, Daniela,Loreto, Maria Antonietta,Gasperi, Tecla,Bernini, Roberta
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p. 6848 - 6854
(2007/10/03)
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- Oxidative cleavage of a cyclobutane pyrimidine dimer by photochemically generated nitrate radicals (no(3)*).
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[reaction: see text] Photochemically generated nitrate radicals (NO(3)(*)) cleave the stereoisomeric N,N-dimethyl-substituted uracil cyclobutane dimers 1a-d into the monomeric uracil derivative 2 as the major reaction pathway. A preferred splitting of the syn dimers 1a,b was observed. The reaction is expected to proceed through initial one-electron oxidation with formation of an intermediate cyclobutane radical cation 11. In addition to cycloreversion, competing reaction steps of 11, which lead to the observed byproducts, are suggested.
- Krueger,Wille
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p. 1455 - 1458
(2007/10/03)
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- The photocycloaddition reactions of uridine and related compounds with 2,3-dimethyl-2-butene
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The photochemical reactions of uracil and 5-fluorouracil derivatives with simple alkenes have been investigated. Photocycloaddition of uracil or 5-fluorouracil derivatives and 2,3-dimethyl-2-butene in acetone gave an enantiomeric mixture of cross cycloadducts (4, 7) in moderate yields. Under similar conditions, diastereomers of 4-substituted 7,7,8,8-tetramethyl-cis-2,4-diazabicyclo[4.2.0]octane-3,5-dione nucleosides (14-17) were formed from uridine or 5-fluorouridine derivatives in good yields. The structures and stereochemistry of these cycloadducts of the nucleoside series were elucidated on the basis of the proton nuclear magnetic resonance spectra and X-ray crystallographic analysis.
- Ishikawa,Itoh,Takayanagi,Oshima,Kawahara,Mizuno,Ogura
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p. 1922 - 1930
(2007/10/02)
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- SYNTHESIS OF REGIOSPECIFICALLY SUBSTITUTED PYRIMIDYL DERIVATIVES AND THEIR INCORPORATION INTO PENEMS
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Syntheses of regiospecifically substituted pyrimidines are described.Depending on the reaction conditions, N1- or N3-substituted pyrimidines are obtained.It has been shown that substitution on uracil under Mitsunobu conditions yields N1-substituted products.Incorporation of these derivatives into the penem nucleus gives penem antibiotics with extremely long half-lives.
- Capraro, Hans-Georg,Lang, Marc,Schneider, Peter
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p. 643 - 652
(2007/10/02)
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- Reactions with Dimethyl Carbonate, 5 Methylation of the Pyrimidine Bases of Nucleic Acids
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The methylation of the pyrimidine bases of nucleic acids by dimethyl carbonate is described compared to dimethyl sulphate.The reaction needs higher temperature, a base and the help of 18-crown-6 and DMF as cosolvent. - Keywords: Dimethyl Carbonate, Methylations, Pyrimidine Bases of Nucleic Acids
- Jansen, Helmut in de Wal,Lissel, Manfred
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p. 863 - 865
(2007/10/02)
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- SYNTHESIS OF 1,3-DIOXIN-4-ONES AND THEIR USE IN SYNTHESIS. XI. 2,2-DIMETHYL-1,3-DIOXIN-4-ONE AS A SYNTHETIC EQUIVALENT OF FORMYLKETENE: SYNTHESIS OF HETEROCYCLIC COMPOUNS
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Cycloaddition of formylketene generated in situ by thermolysis of 2,2-dimethyl-1,3-dioxin-4-one with N-benzhydrylidenebenzylamine yields 3-benzyl-2,2-diphenyl-1,3-oxazin-4-one.Analogous reactions with a carbodiimide, cyanamide, and keteneacetal afford the corresponding 4 + 2 cycloadducts.Reaction of formylketene with 3-amino-2-butenamides affords 4-hydroxy-2-pyridones having a C-2 unit at the 3-position.Keywords: 1,3-dioxin-4-one;formylketene; cycloaddition;1,3-oxazin-4-one; 4-pyrone; 3-acetyl-4-hydroxy-2-pyridone; thermolysis; uracil derivative.
- Sato, Masayuki,Yoneda, Naoki,Kaneko, Chikara
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p. 621 - 627
(2007/10/02)
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- REACTION OF 1-METHYLURACIL WITH PHENYLBENZHYDRAZONOYL CHLORIDE
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The ambident anion of 1-methyluracil gives with phenylbenzhydrazonoyl chloride, depending on the conditions, the N-acylation product (polar solvent, room temperature), or the O-acylation product (nonpolar solvent, heating), which rearranges to a cytosine derivative.Convenient methods have been developed for the preparation of 6-methyl-1,3-diphenyl-5,6-dihydro-5-oxopyrimidotriazolium chloride, a fluorescent derivative of 1-methyluracil, from the N-acylation product, and for the rapid base cleavage of the uracil ring under very mild conditions.
- Chernyshova, N. B.,Shibaev, V. N.
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p. 532 - 538
(2007/10/02)
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- On the Oxidation of N-Methyl and N-Benzylpyrimidin-2- and -4-ones by Rabbit Liver Aldehyde Oxidase
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The presence of a methyl or benzyl group at N-1 or N-3 of 2- and 4-pyrimidone does not affect the site of oxidation by rabbit liver aldehyde oxidase.From all substrates studies only one product viz. the corresponding N-1 or N-3 substituted uracil has been obtained.The maximum rates of oxidation by free enzyme show an optimum in the pH range 6.5-7.8, which is little influenced by the site and the size of the N-substituent.Application of immobilized enzyme in small scale synthesis gives 1- or 3-R-uracils (R = methyl, benzyl) in 43-78percent yield.
- Angelino, S. A. G. F.,Buurman, D. J.,Plas, H. C. van der,Mueller, F.
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p. 749 - 752
(2007/10/02)
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