1.3.5- Triazines imidazoles

Scheme 6.270 Cycloaddition of polymethylene-tethered imidazole/triazine pairs.

Examples Cisplatin, Imidazole Triazines, Hycanthone, Pipobroman,... 

Snyder et al. reported the use of NH4OAC acting as an energy-transfer agent, surprisingly, to perform the intramolecular Diels-Alder cycloaddition depicted in Scheme 11.9, in o-dichlorobenzene under pressure. Cycloaddition of the imidazole/triazine-tethered partners 29 was complete within 20 to 30 min under the action of microwave irradiation at 210-225 °C, producing the pure cycloadducts 30 in 56-85% yields. By the conventionally heated process (under reflux in diphenyl ether at 259 °C) the yields were comparable but required 1.5-5 h to... 

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. 

Construction of the imidazole ring onto a triazine has been also used for the synthesis of this group of compounds. The reaction of 3-aminobenzofl, 2,4]triazine with a-bromoacetaldehyde acetal gave the [1,2-b] linear isomer. On the other hand, the similar reaction on 1-oxide 461... 

Tetrahydroimidazo[5,l-c][l,2,4]triazine 474 was prepared (79KGS1540) by treating imidazole derivatives 472 or 473 with hydrazine. Compound 473 was obtained by reaction of the respective imidazole with 1,2-dibromoethane or by the reaction of the alcohol derivative 471 with phosphorus tribromide. On the other hand, chlorination of471 with thionyl chloride gave 472 (Scheme 100). 

The reactivity of 4-phenylimidazo[5,l-c][l,2,4]triazin-8-carboxamide 485 toward hydrazine has been studied [82JCS(P 1) 1811], whereby pyrazol-4-ylidenehydrazino)imidazole-4-carboxamide 486 was formed (Scheme 102). 

Triphenylphosphoranylidenamino)-arylidineamino]imidazoles 546 with alkyl or arylisocyanates gave (89S843) imidazo[5,l-/][l,2,4]triazines 547 (Scheme 113). 

The number of possible triazinobenzimidazoles is less than that for imidazolotriazines when fusion of the triazine ring takes place on the imidazole ring. It should be noted that z in imidazotriazines indicates the edge of the triazine ring, whereas in the triazinobenzimidazoles it indicates the edge of the benzimidazoles. 

Die Reduktion kann bis zum 3-Oxo(Thiono)-5,6-diphenyl-hexahydro-l,2,4-triazin weitergeftihrt werden, dabei wird jedoch beim 3-Oxo-tetrahydro-Derivat in Acetonitril bei pH — 1 (-1,0 V) unter Ringverengung das 2-Hydroxy-4,5-diphenyl-imidazol (50% d.Th. F 318°) gebildet. Zur Reduktion der N-Alkyl-l,2,4-triazinone s, S. 613. 

Hydroxy leuco bases can be converted into the corresponding amino leuco bases by allowing the leuco compound to react with a secondary amine in the presence of acetic acid.78 Examples, 54, of amine bases utilized in this manner are imidazole, 1,2,4-triazine, aryl amine, and cyclohexayl amine. 

Another example of the remarkable reactivity of Mg actuated by our procedure is its reaction with nitriles. In this respect, the Mg resembles an alkali metal more than an alkaline earth. Benzonitrile reacts with Mg overnight, in refluxing DME, to give 2,4,6-triphenyl-l,3,5-triazine and 2,4,5-triphenylimidazole in 26 and 27% yield, respectively, based on magnesium. Jhe imidazole was shown to arise, at least in part, from the action of Mg on the triazine. The trimerization of aromatic nitriles to give symmetrical triazines is not unknown, but generally the reactions are... 

The [4+2] cycloaddition of dimethyl-1,2,4,5-tetrazine-3,6-dicarboxylate 41 with ketene A, O-acetals or cyanamide yielded tetrafunctionalized pyridazines 42 or 1,2,4-triazine 43 respectively. Treatment of 42-43 with zinc dust in AcOH afforded pyrrole 44 or imidazole 45 derivatives <06S1513>. 

HPA = (4-pyridylthio)aceticacid 2-fur = 2-furoate a-fur = a-furoate = ([Pg.116]

Reactive halogen crosslinkers are mainly specific for sulfhydryl groups at physiological pH, however at more alkaline pH values they can readily cross-react with amines and the imidazole nitrogens of histidine residues. Some reactivity with hydroxyl-containing compounds also may be realized, particularly with dichloro-s-triazine derivatives under alkaline conditions. 

An even more complex pathway involving inverse-electron-demand Diels-Alder reactions between imidazoles and 1,2,4-triazines linked by a tri- or tetramethylene... 

Investigation of l,2,3,7-tetrahydroimida/o[ l, 2-3][l,2,4]triazin-7-onc 56 revealed the /ram-rclationship between the substituents in positions 2 and 3 <2003OL4595>. The (Oil)0-6 (3)-C(2)-0(0Ft) dihedral angle confirmed this geometric feature, whereas it has been shown that the imidazole ring is nearly planar. 

Two different fused imidazoles, imidazo[2,l-f][l,2,4]triazines (extensive literature data) and imidazo[5,W][l,2,4]tria-zines (much less information), are discussed in this section. 

All synthetic approaches to imidazo[2,l-f][l,2,4]triazines published during recent years utilize the ring closure of the six-membered triazine ring by conversion of a properly functionalized imidazole compound. 

Electrolyses at the second reduction step of triazine derivatives in acidic medium, can produce substituted imidazole derivatives as illustrated in Scheme 160 for... 

Both 3-diazO 1,2,4-triazoles and 4-diazo-l,2,3-triazoles easily give cycloaddition reactions with ynamine leading to 4-aminotriazolo-triazine 284 and the yields are generally higher than in the pyrazole and imidazole series (77S556) (Scheme 85). 

Some of the ring expansion reactions discussed in Section 2.03.3.3.1 can be extended to five-membered heterocycles containing two or more heteroatoms. Reaction of imidazoles and pyrazoles with dichlorocarbene, for example, gives chloropyrimidines together with small amounts of chloro-pyrazines or -pyridazines, and oxidative ring expansion of 1-aminopyrazole with nickel peroxide gives 1,2,3-triazine (this, in fact, constitutes the only known synthesis of the unsubstituted triazine). There are, however, a number of interesting and useful transformations which are unique to five-membered polyheteroatom systems. 

---