Uracil 1,3-dimethyl-, reaction with

Electron-rich 6-[(dimethyl(amino)methylene)amino uracil 82 underwent [4+2] cycloaddition reactions with various in situ generated glyoxylate imine and imine oxides to afford novel pyrinhdo[4,5-J]pyrimicline derivatives 83-84 after elimination of dimethylamine from the (1 1) cycloadducts and oxidative aromatization. This one-pot procedure yielded excellent yields when carried out in the solid state and under microwave irradiation <06BMCL3537>. 

The deoxyuracil derivatives-2-hydroxypyrimidine (69) (2-pymoH), 4-hydroxy-pyrimidine (70) (4-pymoH), 4,6-dimethyl-2-hydroxypyrimidine (71) (2-dmpymoH), and pyrimidine (72) (pym), shown here as the minor tautomer, have provided metallacalixarenes having closer resemblance to classical calixarenes, as compared with those obtained from uracil. The reactions of [(en)M(H20)2KN03)2 (M = Pd and Pt ) with 2-pymoH in water gave tetranuclear metallacalixarenes [(en)Pd(2-pymo-N2 N3)]4(N03)4 (73) and [ en)Ft 2-pjmo-Nl N3MN03)2 (74) (2000IC2301). As compared with uracil-based systems, the appearance of one set of resonances for each of pyrimidine PI, in their IT NMR spectra showed fast... 

Aromatic compounds can participate in both [2+2] and [4+2] photocycloaddition reactions with uracil derivatives to give either benzocyclobutane or ethenoquinazoline (barrelene) derivatives, which can then undergo a number of subsequent photochemical reactions. The products obtained are dependent upon the reaction conditions, and thus the photocycloaddition reaction between naphthalenes 470 and l,3-dimethyl-5-fluorouracil 471 in cyclohexane gave 4a-fluoro-5,10-ethenobenzo[/]quinazolines 472 as products as a result of a [4+2] photocycloaddition (photo-Diels-Alder) reaction <2002TL3113, 2003H(61)377>. 

Dimethyl- and l,3-dimethyl-5-halo-substituted uracil derivatives react with cesium fluor-oxysulfate under mild reaction conditions. The reaction carried out in an acetonitrile/water mixture or in an alcohol (methanol, ethanol, propan-2-ol or /a7-butyl alcohol) results in the regioselective formation of 5-fluoro-6-hydroxy- or 6-alkoxy-5-lluoro-l, 3-dimethyl-5,6-dihydro-uracil derivatives 27, respectively, while the stereochemistry of the reaction is strongly syn predominant.29... 

Recently Bredereck and his students have compared the reactivity of a variety of amide complexes in their reaction with 4-amino-l,3-dimethyl-uracil( ) and they came to the conclusion that a mixed carbonyl chloride, phosphorus oxychloride amide complex is the most reactive reagent. 

Uracil reacts with hydrazine to give pyrazol-3(2if)-one (944) and urea N-methyl- and dimethyl-hydrazine behave similarly to give the 2-methyl- and 1,2-dimethyl derivatives. The reactions of hydrazines with uridine and related nucleosides and nucleotides is well studied (67JCS(C)1528). The tautomerism and predominant form of uracil are discussed in Section 2.13.1.8.4. 

Indirect evidence for the formation of anionic adducts has been obtained for some dehalogenation reactions of 5-haIouracils or 5-halo-5,6-dihydro-uracils with bisulfite ion in water.163"165 However, no adducts were detected in the course of these reactions. Similarly, the formation of adduct 120 was assumed in the reaction of 6-bromomethyl-l,3-dimethyl-5-nitrouracil with KCN to yield 6-cyano-l,3-dimethyl-5-nitrocyclothymine.166 Clearly, in all these reactions involving the uracil system, the ring charge delocalization is quite limited, and the resulting stability of the adducts is markedly reduced. 

Substituted uracils 1 are of much interest due to their possible use as anti-cancer and anti-AIDS drugs, and both 2,4-dimethoxy-6-iodopyrimidine and l,3-dimethyl-6-iodouracil (1, R = Me, X = I) were required as starting materials for the synthesis of a variety of uracils 1 by palladium-catalysed C-C bond formation. It was reported in 1961 that treatment of 6-chloro-2,4-dimethoxypyrimidine with sodium iodide in refluxing DMF gave a 42% yield of the corresponding 2,4-dimethoxy-6-iodopyrimidine, but repetition of the reaction recently clearly established that the product was in fact the isomeric l,3-dimethyl-6-iodouracil (1, R = Me, X = I). 

Reaction of various aromatic or heteroaromatic diamines with iV-acyl isothiocyanates gave the corresponding benzo- or heterocycle-fused l,3,5-triazepine-2-thiones, for example, 16 (Figure 3) from 5,6-diamino-1,3-dimethyl-uracil and D-gluconyl isothiocyanate <1981CPB1832>. Cycloaddition of iVjiV -disubstituted ethylenediamines with bis(isocyanato)dimethylsilane or bis(isothiocyanato)dimethylsilane followed by treatment with 1,1 -carbonyldi-imidazole or 1,1 -thiocarbonyldiimidazole afforded a series of 1,5-disubstituted l,3,5-triazepine-2,4-diones, -2,4-dithiones, and 4-oxo-l,3,5-triazepine-2-thiones <1980AGE327>. 

An intramolecular Mannich-type cyclization of l,3-dimethyl-6-(2-aminophenylthio)uracil (120) has been utilized for the synthesis of 5, 6-dihydropyrimido[4,5-b][ 1,5]benzothiazepine-2,4( 1H,3//)-diones (121) this synthesis was realized by reaction of 120 with an excess of formaldehyde, benzaldehyde, or p-nitro- or p-methoxybenzaldehyde in chloroform in the presence of a catalytic amount of p-toluenesulfonic acid under reflux for 4-10 hours. The thiazepine cyclization using aliphatic aldehydes other than formaldehyde did not give satisfactory results. In these cases the reaction resulted in the formation of a dimeric product that probably... 

A new synthesis of purines is illustrated by the reaction of l,3-dimethyl-6-aminouracil with MiV-dimethyldichloromethyleneiminium chloride (phosgeneiminium chloride), trimethylsilyl azide and arylamines in dry chloroform, followed by treatment with 20% aqueous potassium hydrogen carbonate. The reaction probably proceeds via a 4-amino-5-(chloroformamidin-l -yl)uracil (Scheme 10) [94JHC1185],... 

The most common synthetic approaches to both types of pyrimidopyrimidine have been described in CHEC-I and in review articles by Delia . In addition some new strategies in the preparation of pyrimido[4,5-rf]pyrimidines have been developed in the last few years. A new approach is the aza-Wittig-type reaction of iminophosphoranes of 5-aminouracils with aromatic isocyanates which leads to functionalized pyrimido[4,5-rf]pyrimidines. Ethyl 1,3-dimethyl-6-(triphenylphosphoranylideneamino)-uracil-5-carboxylate (105) reacts with isocyanates via adduct (106a) intermediates to afford 7-ethoxypyrimido[4,5-. 

Azine approach. l,3-Dialkyl-6-hydrazinouradl is susceptible to electrophilic attack at C-5. Treatment of (736 R1 = H) with excess thionyl chloride at room temperature gives the fused uracil (737) in an exothermic reaction. The reaction is thought to involve initial formation of a sulfinyl chloride. Subsequently the electrophilic cyclization occurs at C-5 to form a thiazoline S-oxide which is dehydrated to yield (737). From a,3-dimethyl-6-hydrazinouracil (736 R1 = R3 = Me, R2 = H) the heteroaromatic betaine (738) is formed (78JOC1677). 

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