1.3- Dimethyluracil, oxidation

The 1,3-dimethyluracil derivative 109 with two reactive centers reacts with 1,2,4-tiiazine 4-oxide 58 only at the uracil fragment to afford compound 110 (96MC116). 

Anilinofervenulin 4-oxides 151 were synthesized by the reaction of 6-hydra-zino-l,3-dimethyluracil with triethyl orthoformate, followed by the treatment of the hydrazide 152 with aniline and further cylization of 153 in the presence of potassium nitrate in acetic acid (82JHC1309). 

Phenyl-l,2,4-triazine 4-oxide 91 reacts with l,3-dimethyluracil-6-hydrazones 92 in DMF in the presence of triethylamine to give pyrazolo[3,4-. 

The addition of organometaiiics to unactivated pyrimidines normally produces unstable dihydro derivatives which readily oxidize back to the pyrimidine oxidation level, although successful conjugate addition to pyrimidinone derivatives can occur. Thus, the addition of lithium trimethylsilyldiazomethane [TMSC(Li)N2] to 1,3-dimethyluracil 418 occurred at the 6-position to produce a mixture of the two pyrazolo[4,3-rf]pyrimidine-5,7-diones 419 and 420, where the initial addition had been accompanied by cyclization <1997T7045>. 

Finally, an unusual approach to pyrrolo[2,3- pyrimidines is seen in Equation (40). The dimethyluracil 113 is presumed to form the A -oxide at the exocyclic nitrogen atom. This then undergoes a [2,3]-sigmatropic rearrangement followed by a [3,3]-sigmatropic rearrangement, tautomerization, and cyclization to give 114 <200581164>. 

Reaction of 6-amino-l,3-dimethyluracil with the Mannich base 524 under nitrogen in boiling H2O gave 5,6-dihydropyrido[2,3- pyrimidine-(17/,37/)-2,4-diones 531 rather than their oxidized analogues 530. The latter could be obtained by boiling the reactants in AcOH (Scheme 22) <2004T11511>. 

N-, 0-, and S-heterocyclic ligands also form [Os(NH3)5 t)2-(C,C)-L ]2+ complexes [L = 2,6-lutidine, 2,6-lutidinium, pyridinium, N-methylpyridinium, and lV-methyl-4-picolinium (85, 167), NJV -dimethylimidazolium (90), pyrrole (90, 179), IV-methylpyrrole (90, 179), thiophene (90,179), furan (90,179), and 1,3-dimethyluracil (72, 73)]. On oxidation to Os(III), arene ligands are rapidly lost from the coordination sphere, or in the case of the substituted arene ligands with good a donors, rapid linkage isomerization reactions occur (Section V,D). 

Some oxidations of heterocyclcs with two heteroatoms proceed very readily. Thus, fluorinated quinazoline is oxidized to quinazol-4-one on fusing for only 2 minutes (Table 16).264 On the other hand, more vigorous oxidation of 5-fluoro-l,3-dimethyluracil by 3-chloroperoxybenzoic acid leads to the formation of unstable intermediate radicals that tend to rearrange to 4-hy-droxy-l,3-dimethylimidazoledione 3-chlorobenzoate (Table 16), similar177 to the chemical behavior of trifluoromethylated phenol.265... 

Oxidation of S-fluoro-1,3-dimethyluracil by m-chloroperoxybenzoic acid leads to 4-hydroxy-1,3-dimethylimidazoledione m-chlorobenzoate [SO] (equation 72). 

Schuchmann H-P, von Sonntag C (1988) The oxidation of methanol and 2-propanol by potassium peroxodisulphate in aqueous solution free-radical chain mechanisms elucidated by radiation-chemical techniques. Radiat Phys Chem 32 149-156 Schuchmann H-P, Wagner R, von Sonntag C (1986) The reactions of the hydroxymethyl radical with 1,3-dimethyluracil and 1,3-dimethylthymine. Int J Radiat Biol 50 1051-1068 Schuchmann MN, von Sonntag C (1982) Determination of the rate constants of the reactions C02 + OH" -> HC03 and barbituric acid —> barbiturate anion + H+ using the pulse radiolysis technique. Z Naturforsch 37b 1184-1186... 

Oxidative Cleavage of the 1,3-Dimethyluracil-derived Cyclobutane Dimers 1 by Nitrate Radicals (N03 )... 

Treatment of the easily obtainable 2-thiouracil with chloracetic acid followed by acid hydrolysis (08J A547 52MI1) or by oxidation with dimeth-ylsulfoxide (DMSO) in cone, sulfuric acid (74S491) are alternative pathways. 1,3-Dimethyluracil is transformed with urea in ethanolic sodium ethoxide into uracil (77JHC537 78JOC1193). 

Azido-5-formyl-l,3-dimethyluracil is cyclized with hydrazines to afford pyrazolo[3,4-reaction with triphenylphosphine in benzene result in the formation of isoxazolo[3,4-c/]pyrimidine and pyrimido[4,5-[Pg.182]

MI1 74MI7). The acetates of these acydo C-nucleosides (539, R = Ac) were obtained by oxidative cyclization of the Schiff bases 540, derived from aldehydo-sugar acetates 180 and 4,5-diimino-l,3-dimethyluracil, with mercury(II) chloride in dimethyl sulfoxide [79CPB1094, 79H(12)359] (Scheme 144). 

In a palladium-mediated oxidative coupling reaction, alkenes such as methyl acrylate, acrylonitrile, or styrenes cyclize with 6- [(diinethylainino)methylene]amino -l,3-dimethyluracil to give the corresponding 6-substituted pyrido[2,3-[Pg.128]

Further studies of the photochemically induced conversion of JV-methyl-diphenylamine into N-methylcarbazole have been reported.28 Two successive intermediates have been detected, namely the amine triplet and iV-methyl-4a,4b-dihydrocarbazole. Oxygen appears to participate in the overall reaction in two ways, viz. by dehydrogenation of the dihydrocarbazole intermediate to carbazole and by quenching the amine triplet. Non-oxidative cyclization of 5-(iV-methyl-anilino)- and 5-(iV-acetylanilino)-l,3-dimethyluracil (26) similarly gives the trans-dihydropyrimido[5,4-6]indoles (27) in high yield.24 Orbital symmetry arguments... 

The 7-(alditol-l-yl)-l,3-dimethylpteridine-2,4-diones 671 were the only products obtained from the reaction of aldehydo-sugar acetates (180) with 5,6-diamino-l,3-dimethyluracil (669) followed by oxidative cyclization of... 

Pulse radiolysis shows that the pyrimidine radical cations are fairly strong acids and rapidly deprotonate at a heteroatom [reaction (98)]. As protonation/deprotonation reactions at heteroatoms are easily reversible, the radical cations are regenerated upon reprotonation. Deprotonation at carbon or reaction with water yields the final free-radical products [reactions (99) - (101)]. It is noted that in thymidine [23] and 5 -thymidylic acid [104] the allylic thymine radical is observed by EPR and there is very little question that its precursor is the thymine radical cation. The identification of the C(6)-OH-5-yl radical by EPR supports the view [100] that reaction with water competes with the deprotonation at methyl. Due to the ready oxidation of the (reducing) C(5)-OH-6-yl by peroxodisulfate, this type of radical is only observed at low peroxodisulfate concentrations in these systems, i.e. the (oxidizing) C(6)-OH-5-yl radicals are correspondingly enriched under conditions favourable to a chain reaction [22]. In the case of 1,3-dimethyluracil the interesting characteristics of... 

The carbocation may recombine with either of the two anions or react with water [reactions (103)-(105)]. When the carbocation combines with the sulfate radical [reaction (105)], an oxidizing species is formed which, however, is not as reactive as the sulfate radical but nevertheless contributes to the propagation of the chain with a slow rate k = 1.2 x 10 dm mof s ), and thus the chain length becomes dependent on the 1,3-dimethyluracil concentration. 

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