3.5.6- Triaryl-1,2,4-triazines

When l,3r5-triazine is allowed to react with dinitrogen pentoxide and quenched with methanol the cis and trans isomers of 13 3-trinitro-2,4,6-trimethoxy-hexahy drotriazine are obtained. Nitration of the triazine in deuterated nitromethane at -10 °C affords the mixture of cis and trans 2,4,6-trinitrato-l,3,5-trinitro-hexahydro-13,5-triazines which are decomposed at room temperature . Hexahydro-13,5-triaryl-133-triazines cyclorevert upon exposure to HC1 gas to give solid arylmethylene iminium chlorides as new versatile reagents... 

All the well-characterized 1,2,3-triazine derivatives are stable, high-melting solids. The 4,5,6-triaryl derivatives show UV maxima in the range 259-286 nm (log e = 4.09-4.42), 4,5-diphenyl-1,2,3-triazine has Amai at 251 nm, while the 4,5,6-trimethyl derivative shows two maxima at 217 nm (log e — 3.63) and 278 nm (log e = 2.79). Mass spectral studies indicate that fragmentation takes place in an identical fasMon to that observed during photochemical decomposition, i.e., with production of acetylenes, nitriles, and nitrogen. ... 

Triaryl-l, 3,5-triazine reagieren in Essigsaure unter reduktiven Bedingungen wie der ka-talytischen Hydrierung bei 15 MPa mit Raney-Nickel als Katalysator439 oder der Reduktion mit Zink440 zu den entsprechenden 2,4,5-Triaryl-imidazolen (53-87%) ... 

Aus 2,4,5-Triaryl-imidazolen konnen durch Belichten in Methanol in Gegenwart von Ammo-r.iiumacetat in Ausbeuten von 30-56% 2,4,6-Triaryl-l, 3,5-triazine hergestellt werden1245 ... 

Grignard reagents add to 1,2,4-triazines. Initial attack at the 5-position is favored (277 — 278 — 279) if this position is substituted the nucleophile adds to the 6-position, and finally to the 3-position. Starting from the parent 1,2,4-triazine, 3,5,6-triaryl-l,2,4-triazines (280) have been prepared by successive addition of Grignard reagents to the ring and oxidation of the dihydro-1,2,4-triazine so formed. 

Most known monocyclic 1,2,3-triazines and 1,2,3-benzotriazines are stable at room temperature. No detailed study of the stability of monocyclic 1,2,3-triazines towards water, aqueous acids or bases has been published, but one can assume from the reaction conditions used in the preparation of monocyclic 1,2,3-triazines, by oxidation of (V-aminopyrazoIes, that they are stable to water, aqueous acids or bases at room temperature, at least for a short time. Treatment of triaryl-1,2,3-triazines with aqueous hydrochloric acid at higher temperatures leads to hydrolysis of the ring and formation of 1,3-dicarbonyl compounds (Scheme 3) (60TL(13)19,76UP21800). 

Aromatic aldazines when treated in boiling toluene with potassium r-butoxide, furnished 3,5,6-triaryl-l,2,4-triazines (632) and their 2,5-dihydro (633) and 1,2,5,6-tetrahydro derivatives (634), besides triazoles, which were the major products (76JCS(Pl)207). The formation of the triazines is best explained by a [4+2] cycloaddition or a two-step process via the carbanion (631) and elimination of benzalimine to give (633), which can be oxidized to (632 Scheme 21). TTie formation of (634) is still in doubt. 

Triaryl-1,3,5-triazines are more readily prepared than are the alkyl derivatives (see Section 2.20.4). In general, the compounds are stable, and 2,4,6-triphenyl-l,3,5-triazine, for example, can be distilled at ca. 350 °C without decomposition. These compounds undergo similar ring-opening reactions to the 2,4,6-trialkyl-l,3,5-triazines, but the reaction requires even more vigorous conditions (see Section 2.20.3.2) <59HC(l3)l, p.178). 

Triazines with three different substituents are formed by variations on the above methods. There is no efficient route to trialkyl or triaryl derivatives, although the reaction of acylimidates and amidines has met with some success (see Section 2.20.4.6.2). In general the best routes available are as follows, (a) Substitution reactions of cyanuric chloride, (b) The condensation of Af-cyanoamidine with chloromethyliminium salts, (c) 2-Aryl-1,3,5-triazin-2-ones may be efficiently prepared by ring closure reactions on AT-(a-chloroalky-lidene)carbamoyl chloride and amidines (see Section 2.20.4.4.1). 

Dandia et al. [29] gave the economic, ecofriendly, facile, one pot synthesis of fluorinated 1,3,5-triaryl hexahydro-l,3,5-triazine (xvii) following the condensation of fluorinated amines with formaldehyde under microwave irradiation in aqueous medium. The target triazines were obtained in excellent yields (98-99%) and showed good activity against the selected fungal strains of Rhizoctonia solani, Fusarium oxyspomm and Collectotrichum capsid. 

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