Triazine, nucleophile reactions with

Base-catalyzed hydrogen exchange, 16, 1 Basicity and acidity of azoles, 41, 187 Behavior of monocyclic 1,2,4-triazines in reactions with C-, N-, O-, and S-nucleophiles, 46, 73 1-, 2-, and 3-Benzazepines, 17, 45 Benzisothiazoles, 14, 43 38, 105 Benzisoxazoles, 8, 277 29, 1 Benzoazines, reactivity with nucleophiles,... 

Behavior of Monocyclic 1,2,4-Triazines in Reactions with C-, N-, O-, and S-Nucleophiles... 

Cyanuric fluoride behaves much the same as cyanuric chloride but its higher reactivity leads to nucleophilic reactions with aromatic amines, which act as carbon nucleophiles. This is a useful advantage for cyanuric fluoride, as a synthetic reagent, for the synthesis of these triazine derivatives with carbon substituents. 

The catalytic effect of protons has been noted on many occasions (cf. Section II,D,2,c) and autocatalysis frequently occurs when the nucleophile is not a strong base. Acid catalysis of reactions with water, alcohols, mercaptans, amines, or halide ions has been observed for halogeno derivatives of pyridine, pyrimidine (92), s-triazine (93), quinoline, and phthalazine as well as for many other ring systems and leaving groups. An interesting displacement is that of a 4-oxo group in the reaction of quinolines with thiophenols, which is made possible by the acid catalysis. 

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. 

An 8000-member library of trisamino- and aminooxy-l,3,5-triazines has been prepared by use of highly effective, microwave-assisted nucleophilic substitution of polypropylene (PP) or cellulose membrane-bound monochlorotriazines. The key step relied on the microwave-promoted substitution of the chlorine atom in monochlorotriazines (Scheme 12.7) [35]. Whereas the conventional procedure required relatively harsh conditions such as 80 °C for 5 h or very long reaction times (4 days), all substitution reactions were found to proceed within 6 min, with both amines and solutions of cesium salts of phenols, and use of microwave irradiation in a domestic oven under atmospheric reaction conditions. The reactions were conducted by applying a SPOT-synthesis technique [36] on 18 x 26 cm cellulose membranes leading to a spatially addressed parallel assembly of the desired triazines after cleavage with TFA vapor. This concept was later also extended to other halogenated heterocycles, such as 2,4,6-trichloropyrimidine, 4,6-dichloro-5-nitropyrimidine, and 2,6,8-trichloro-7-methylpurine, and applied to the synthesis of macrocyclic peptidomimetics [37]. 

In Scheme 7, ring-opening reactions of some fused pyrazoles are shown. Thus, Baraldi et al. <1999S453> described that the pyrazolo[l,5-<7][l,2,4]triazine-dione derivative 72 is sensitive toward nucleophiles its reaction with benzylamine at room temperature gives rise to the acyl semicarbazide 73 in high yield (78%). 

In the reactions with phosphonio-a-methoxycarbonyl-alkanides, the products of type 261 derived from 1,3-cycloaddition can rearrange to the tautomeric lif-pyrazolo-triazole (87MI2). The reaction of 3-diazopyra-zoles and 3-diazoindazole with acyl-substituted phosphonium ylides led to pyrazolo-triazine and indazolo-triazine derivatives 266 instead of the expected triazole compounds (8IJHC675). In this case, the ylides, which can exist as phosphonium enolates, possess nucleophilic and electrophilic centers in a /8-relationship, giving [7 + 2] or [11 -I- 2]cycloaddition reactions. With dimethylsulfonio-a-aroyl-methanides, very complex, temperature-dependent mixtures were obtained, in some cases with sulfur retention (87MI3). 

Nucleophilic substitution with heteroaryl halides is a particularly useful and important reaction. Due to higher reactivity of heteroaryl halides (e.g. 35, equation 24) in nucleophilic substitution these reactions are widely employed for synthesis of Al-heteroaryl hydroxylamines such as 36. Nucleophilic substitution of halogen or sulfonate functions has been performed at positions 2 and 4 of pyridine , quinoline, pyrimidine , pyridazine, pyrazine, purine and 1,3,5-triazine systems. In highly activated positions nucleophilic substitutions of other than halogen functional groups such as amino or methoxy are also common. 

Nucleophilic substitution of the 4-chloro group of the 4-pyranotriazines 103 with hydrazine gives the 4-hydrazino-triazines 104, which can be further elaborated to the corresponding azides 105 or cyclized upon reaction with formic acid or carbon disulfide to give the triazolotriazines 106 or thioxotriazolotriazines 107, respectively (Scheme 11) <2005HC0495>. 

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