Triazines aromaticity

On the basis of the analysis of the CD spectra by the nonempirical DeVoe approach, it was possible to establish that each l-(l-naphthyl)ethylamino moiety assumes the same closed conformation with respect to the r-triazine aromatic ring (dihedral angle naphthalene-triazine, 90°), independently of the number or absolute configuration of the other l-(l-naphthyl)ethylamino groups linked to the r-triazine moiety <1998JOC8765>. 

Many chemical compounds have been described in the Hterature as fluorescent, and since the 1950s intensive research has yielded many fluorescent compounds that provide a suitable whitening effect however, only a small number of these compounds have found practical uses. Collectively these materials are aromatic or heterocycHc compounds many of them contain condensed ring systems. An important feature of these compounds is the presence of an unintermpted chain of conjugated double bonds, the number of which is dependent on substituents as well as the planarity of the fluorescent part of the molecule. Almost all of these compounds ate derivatives of stilbene [588-59-0] or 4,4 -diaminostilbene biphenyl 5-membeted heterocycles such as triazoles, oxazoles, imidazoles, etc or 6-membeted heterocycles, eg, coumarins, naphthaUmide, t-triazine, etc. 

Organic Derivatives. Although numerous mono-, di-, and trisubstituted organic derivatives of cyanuric and isocyanuric acids appear in the hterature, many are not accessible via cyanuric acid. Cyanuric chloride 2,4,6-trichloro-j -triazine [108-77-0], is generally employed as the intermediate to most cyanurates. Trisubstituted isocyanurates can also be produced by trimerization of either aUphatic or aromatic isocyanates with appropriate catalysts (46) (see Isocyanates, organic). Alkylation of CA generally produces trisubstituted isocyanurates even when a deUberate attempt is made to produce mono- or disubstituted derivatives. There are exceptions, as in the production of mono-2-aminoethyl isocyanurate [18503-66-7] in nearly quantitative yield by reaction of CA and azitidine in DMF (47). 

All of the general classes of cr -adduct aromatization were found to occur in the reactions of 1,2,4-triazine A-oxides with various nucleophiles. From this point of view, the 1,2,4-triazine A-oxides are a very convenient substrate for the Sj reaction studies. 

The isolated cr -adducts 57 undergo oxidation with KMn04 easily, resulting in the corresponding 5-indolyl-1,2,4-triazine 4-oxides 60 (98ZOR429). Separating the nucleophilic addition step from the oxidative aromatization of the intermediate (T -adducts allows the use of such oxidant-sensitive nucleophiles as indoles. 

The reaction of 1,2,4-triazine 4-oxides 55 with CH-active 1,3-diketones (dime-done, indanedione, iV.iV -dimethylbarbituric acid) in the presence of trifluoroacetic acid (substrate activation by protonation) or KOH (activation of the nucleophile) leads to stable cr -adducts 63, whose oxidative aromatization by the action of KMn04 results in 5-substituted 1,2,4-triazine 4-oxides 64 (98MI). 

It was found that 1,2,4-triazine 4-oxides 55 are active enough to react with cyanamide under basic conditions according to the deoxygenative mechanism to form 5-cyanamino-l,2,4-triazines 73 (00TZV1128). This reaction seems to be facilitated by the easy aromatization of cr -adducts by the Elcb elimination of water. 

Another pathway for the aromatization of the cr -adducts was found in the reactions of 3-pyrrolidino-l,2,4-triazine 4-oxide 81 with amines. Thus the treatment of 1,2,4-triazine 4-oxide 81 with ammonia leads to 5-amino-1,2,4-triazine 4-oxides 54—products of the telesubstitution reaction. In this case the cr -adduct 82 formed by the addition of ammonia at position 5 of the heterocycle undergoes a [l,5]sigmatropic shift resulting in 3,4-dihydro-1,2,4-triazine 83, which loses a molecule of pyrrolidine to yield the product 54. This mechanism was supported by the isolation of the key intermediates for the first time in such reactions—the products of the sigmatropic shift in the open-chain tautomeric form of tiiazahexa-triene 84. The structure of the latter was established by NMR spectroscopy and X-ray analysis. In spite of its open-chain character, 84 can be easily aromatized by refluxing in ethanol to form the same product 54 (99TL6099). 

Open-chain tautomerism is a general feature of 4-hydroxy-3,4-dihydro-1,2,4-triazines, including cr -adducts at position 3 of the 1,2,4-triazine 4-oxides. Thus triazahexatrienes 85 are the open-chain form of cr -adducts 86 and can be aromatized by oxidation with KMn04, yielding 3-amino-1,2,4-tiiazine 4-oxides 88 (98ZOR418). 

Aromatic biguanides such as proguanil (181) have been found useful as antimalarial agents. Investigation of the metabolism of this class of drugs revealed that the active compound was in fact the triazine produced by oxidative cyclization onto the terminal alkyl group. The very rapid excretion of the active entity means that it cannot be used as such in therapy. Consequently, treatment usually consists in administration of either the metabolic precursor or, alternately, the triazine as some very insoluble salt to provide slow but continual release of drug. 

The reaction of dimethyl-1,2,4,5-tetrazine-3,6-dicarboxylate 353 with aromatic amines gave (82CB683) pyrazolo[3,4-e][l,2,4]triazines 354 (Scheme 75). 

Condensation of 1,3-diphenyl[ 1,2,4]triazin-6-one 360, obtained from reaction of hippuric acid and phenylhydrazine, with aromatic aldehydes... 

Thiazolotriazines 636 (R = CO,Me) were prepared [84JCS(P1)2707] by cycloaddition of dimethyl acetylenedicarboxylate with triazine derivative 632. Derivatives of thiazolo[3,2-b][l,2,4]triazin-3,7-diones 637 have been formed (74JPR163) on reaction with aromatic aldehydes and diazonium salts to give 636 (R = Ar) and 638, respectively. Regioselective catalyzed... 

The sequential treatment of triazine derivative 990 with acyl chlorides and acetic anhydride and perchloric acid afforded (86H1031) thiadi-azolo[l, 2,4]triazinium perchlorates 991. On the other hand, cyclocondensation of 992 with organic acids gave 993 [82JHC1577 83JAP(K)58/180492] and 994 with aromatic aldehydes (84JIC552) (Scheme 183). 

Peroxides oxidize TPDD to Wurster s blue, a product with a semiquinone diimine structure [1]. Similarly Wurster s blue is also produced from TPDD by reaction with halogen-containing substances produced by the reaction of aromatic amines and triazines with chlorine gas. 

The chromatogram is freed from mobile phase, lightly but homogeneously sprayed with the spray solution or immersed in the dipping solution for 2 s. Triazines and aromatic amines must first be converted to chlorinated derivatives by exposing the chromatogram to chlorine gas (see Procedure Tested ). 

After a few minutes drying in air sterol hydroperoxides, nitrate esters, triazines and aromatic amines yield blue-violet chromatogram zones on a pale blue to violet background [1, 3]. Polynitroaromatics yield yellow to dark beige zones [3]. 

Elimination of nitrogen from D-A adducts of certain heteroaromatic rings has been useful in syntheses of substituted aromatic compounds.315 Pyrazines, triazines, and tetrazines react with electron-rich dienophiles in inverse electron demand cycloadditions. The adducts then aromatize with loss of nitrogen and a dienophile substituent.316... 

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