Heterocyclics triazines

Ferricyanide oxidation of 1,5-disubstituted thiocarbazones (116) give the mesoionic tetrazolium salts (117) under mild conditions (Eq. 21).190 This is in contrast to the strongly alkaline oxidation of carbazides leading to mercapto formazans as shown in Eq. 8 (Section 7.3.1.4). The heterocyclic triazine (118), obtained by the action of a diazonium salt on 2-... 

Triazines and triazole herbicides, such as, atrazine, simazine, metribuzin, or amitrole — These substances contain a heterocyclic triazine ring. 

The synthesis of 9H-benzo[2,l-e]thiazolo-[2,3-c]-as-triazine (401) was achieved by oxydative cyclization of 2-imino-3-(o-aminophenyl)-4-phenyl-4-thiazoline (718, 719). This latter reacts also with paraformaldehyde in hot toluene yielding 3-phenyl-9H.10H-benzo[l,2-/]thiazolo-[2,3-d][l,3,5]triazepine (402) (720). This heterocyclic sytem is also formed when carboxylic acids replace paraformaldehyde (Scheme 230) (721). 

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. 

This reactivity of A-unsubstituted amino-pyrazoles and -indazoles which can be regarded as 1,3-diamino derivatives has been used to build a great variety of fused six-membered heterocycles such as the 1,2,4-triazine derivatives (540) and (541), the 1,3,5-triazine derivatives (542) and (543), and benzothiadiazines (544). 

A heterocyclization involving the N-2 atom of indazole affords [l,2,4]triazino[4,5-h]-indazoles (561) from the 3-carbohydrazinoindazole (78JHC1159,79JHC53). The corresponding pyrazolo[l,5-tf][l,2,4]triazine (562) has been prepared by the same procedure (8UHC1319). 

Certain trifluoromethyl-substituted 1,2,4,5 tetrazines [260, 26i] and 1,2,4 triazines [i06] can be used as cyclic hetero-1,3-dienes and provide efficient preparative routes to partially fluorinated heterocycles (equations 55 and 56)... 

Taylor has reported a number examples of intramolecular variations directed towards heterocyclic systems.The following two reactions are representative. Intramolecular addition of triazine 79, after loss of nitrogen afforded 80. Alternatively, triazine 81 generated bicyclic systems 82 which could be oxidized to 83. 

The formal derivation of the analogs, described in the foregoing, represents, from the point of view of systematic organic chemistry, a shift to the derivatives of other heterocyclic systems. In the case of pyrimidine aza analogs we arc dealing with derivatives of symmetrical or asymmetrical triazine in the case of purine aza analogs, the derivatives produced are those of imidazo[4,5]-i -triazine and z -triazolo [4,5-d] pyrimidine. 

The replacement of a heterocyclic hydroxyl group (generally in the 0X0 form, Section II,E, 2,e) with thioxo or chloro groups by phosphorus pentasulfide or phosphorus oxychloride presumably proceeds through nucleophilic substitution (frequently acid-catalyzed, 21 and 86) of thiophosphoryloxy and dichlorophosphoryloxy intermediates. The 4-position in pyrimidine is more reactive than the 2-position and, at low temperature, this type of thionation of pyrimidine-2,4-diones is specific for the 4-position. In as-triazine... 

The deactivating effect of a phenyl group relative to a CCI3 group on s-triazines is noted below,but comparison with hydrogen as a substituent does not appear to have been reported in heterocycles. 

The reaction of 3-methoxy-1,2,4-triazine 1-oxide 20 with the carbanion generated from chloromethyl phenyl sulfone proceeds as the vicarious nucleophilic substitution (VNS) of hydrogen (Scheme 1, path B) via addition of the carbanion at position 5 of the heterocycle. Following base-induced elimination of HCl and protonation, 3-methoxy-5-phenylsulfonyl-1,2,4-triazine 4-oxides 65 result (88LA627). 

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). 

It is known that 1,2,4-triazine 4-oxides, in contrast to 1,2,4-triazine 1- and 2-oxides, cannot be obtained by oxidation. Therefore, the only way to obtain 1,2,4-triazine containing the A -oxide group at position 4 of the heterocycle is to form the tiiazine ring by cyclization, starting from compounds bearing nitroso (isonitroso) or hydroxylamino groups. There are several ways to carry out such cyclizations. 

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