1.2.4- Triazines base-catalyzed

Base-catalyzed Dimroth rearrangements of l-aryl-4,6-diamino-1,3,5-triazines or triflic acid-induced decomposition of 6-anilino-1,3,5-triazines led to the formation of the corresponding substituted 1,2-dihydro-l,3,5-triazines, whose structure was established on the basis of H NMR spectra (93JHC849). 

Dioxane solutions of 4(5)-aminoimidazole (64) have been treated with several reagents [92JCS(P1)2789], Imidazo[l,5-a]-l,3,5-triazines (65 R = Ph, Me SMe) were obtained by reaction with methyl N-cyanobenzimidate (57 R = Ph), ethyl N-cyanoacetimidate (58 R = Me), and dimethyl yV-cyanodithioiminocarbonate (59 R = SMe). The uncy-clized product (68 R = H) (73%), obtained by condensation with ethyl N-cyanoformimidate (58 R = H), underwent facile cyclization to give the imidazo[l,5-a]-l,3,5-triazine (65 R = H). Likewise, the condensation adduct (69 R = H) (78%) was obtained using ethoxy methyleneurethane (60 R = H) and this underwent base-catalyzed cyclization to give the imidazo[ 1,5-a]-1,3,5-triazinone (67). Imidazo[l, 5-a]pyrimidines (66 R = H, Me) were obtained from the condensation of 4(5)-aminoimidazole... 

Hydrolysis of isofervenulins 268 with aqueous base occurred at the C2—N3 bond to give A -carboxy-TV-methylcarbamoyltriazines 301, which were transformed to 268 by acidification of the reaction mixture. On the other hand, base-catalyzed hydrolysis of 268 gave imidazo[4,5-< ][l,2,4]tri-azines 302 (87KGS1555). Hydrolysis of the pyrimidotriazine derivatives with alkali gave the triazines 303 and 304 (77JPR522 87JPR290). 

Table III summarizes the parameters that affect Brrfnsted acid-catalyzed surface reactions. The range of reaction conditions investigated varies widely, from extreme dehydration at high temperatures in studies on the use of clay minerals as industrial catalysts, to fully saturated at ambient temperatures. Table IV lists reactions that have been shown or suggested to be promoted by Br nsted acidity of clay mineral surfaces along with representative examples. Studies have been concerned with the hydrolysis of organophosphate pesticides (70-72), triazines (73), or chemicals which specifically probe neutral, acid-, and base-catalyzed hydrolysis (74). Other reactions have been studied in the context of diagenesis or catagenesis of biological markers (22-24) or of chemical synthesis using clays as the catalysts (34, 36). Mechanistic interpretations of such reactions can be found in the comprehensive review by Solomon and Hawthorne (37).

Base-catalyzed additions of HCN to s-triazine (1) give 2-cyano-l,2-dihydro-s-triazine (9). Its H-NMR spectrum shows that the hydrogen on the nitrogen is equilibrating rapidly between the 1- and 3- positions. When 9 is heated to 65°C it melts and eliminates HCN (72UP1). 

Subsequently, it was shown that the reaction was catalyzed by base (48M(79)106). Dicyandiamide reacts with nitriles (the most valuable method), amidines, cyanamides, ammonia, cyanates, thiocyanates, carboxylic acids and anhydrides to yield 1,3,5-triazines (Table 13). This synthetic route has been reviewed thoroughly several times (59HC(13)1, p. 219,61MI22000, p. 650, 73ZC408). The base-catalyzed reaction of dicyandiamide with alkyl or aryl nitriles (Scheme 65) proceeds via the imino ether anion and the rate determining step is solvent dependent. In DMSO the formation of the imino ether is rate determining, but in 2-methoxyethanol the reaction between the anion and dicyandiamide controls the rate (66T157). 

Base-catalyzed trimerizations are facile also for example, trifluoromethyl cyanide trimer-izes in the presence of ammonia, presumably through the formation of the amidine intermediate (139 Scheme 77) (67JOC231). Similarly, perfluoro-n-propyl cyanide forms the 1,3,5-triazine in the presence of sodium methoxide, probably via the imidate (140 Scheme 78) (52JA5633). 

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,... 

Steroidal, alicyclic or aromatic annulated pyridines were prepared via a microwave-assisted, base-catalyzed Henry reaction of /1-formyl enamides and nitromethane on an alumina support [97]. Highly substituted tri- and tetrasubstituted pyridines were synthesized in a Bohlmann-Rahtz reaction from ethyl /3-amino crotonate and various alkynones. The reaction involved a Michael addition-cyclodehydration sequence and was effected in a single synthetic step under microwave heating conditions [98]. An alternative approach towards polysubstituted pyridines was based on a reaction sequence involving an inverse electron-demand Diels-Alder reaction between various enamines 45 and 1,2,4-triazines 44 (Sect. 3.6), followed by loss of nitrogen and subsequent elimination-aromatization. Enamines 45 were formed in situ from various ketones and piperidine under one-pot microwave dielectric heating conditions [99]. Furthermore, a remarkable acceleration of the reaction speed (from hours and days to minutes) was observed in a microwave-assisted cycloaddition. Unsymmetrically substituted enamines 45 afforded mixtures of regioisomers (Scheme 35). 

Coordination polymer nanotubes have been prepared using Hg2+-mediated coassembly of two ligands, tetrapyr-idylporphine (TPyP) 128 and tris(4-pyridyl)-l,3,5-triazine (TPyTa) 129 (which is readily formed by the trimerization of 4-cyanopyridine under acid- or base-catalyzed conditions), at the water-chloroform interface <2006CC3175>. 

The triazine 1-oxide (54a) undergoes a base-catalyzed rearrangement to yield the triazolopyridine carboxamide (55). Further heating delivers triazolopyridine (56) (Scheme 1) <62JOC2504>. 

The pyrido-l,2,4-triazines (83) and (85) were prepared in one step from the corresponding nitropyridines (345a,b) by treatment with NaOMe and guanidine, followed by base-catalyzed cyclization <76MI 717-03). 

Second-Order Rate Coefficients for Base-Catalyzed Deuterium-Hydrogen Exchange at C-3 in 5-Substitutf.d 1,2,4-Triazines"... 

In pyridazines, base-catalyzed hydrogendeuterium exchange takes place at positions 4 and 5 more easily than at positions 3 and 6. Pyridazine 1-oxide reacts first at positions 5 and 6 and then at C(3) and C(4). Pyrimidine exchanges most readily at the S-position, next at the 4-position, and least readily at the 2-position. In pyrimidine 1-oxide, the reactivity order is 2>6>4>>5. 1,2,4-Triazines easily undergo base-catalyzed hydrogen exchange at the 2-position. 

Base-catalyzed ring closure of the isothiocyanate derivative (127) gives the pyrazolo-[l,5-a][l,3,5]triazine (128 Scheme 41) <74JHC199>. The sulfur may be removed with Raney nickel in ammonium hydroxide. Another example of this versatile route is the formation of (130) in Scheme 42. However, the starting material (129) also has a hydrazone group... 

II, 2.4]-triazin-3(2/y)-one (151, R = Me, R = H) (70JHCI23I). Similarly, 150 (R = Me) reacts with a-cyanobenzyl p-toluene sulfonate lPhCH(CN)OTS] or a-cyanobenzyl bromide PhCH(CN)Br] to afford 151 (R = Me, R = Ph) (7IJHC62I). Structure 151 was proved by its reduction with diborane to 152, which was also obtained by an independent synthesis involving the reaction of 153 with thionyl chloride followed by base-catalyzed cyclization (70JHCI231 71JHC621). To ascertain whether the methyl group at the I-position in 150 (R = Me) influences the direction of cyclization, the thione 150 (R = H) was allowed to condense with a-cyanobenzyl-p-toluene sulfonate and ethyl a-bromophenylacetate. In both cases 151 (R = H, R = Ph) was obtained. Compound 150, however, on reaction with 1,2-dibromoethane, furnished another bicyclic system (154). The difference in the behavior of 150 toward dibromoethane and other reagents such as ethyl bromoacetate and a-cyanobenzyl p-toluene... 

Omotowa B A, Shreeve J M. Triazine-based polyfluorinated triqua-temary liquid salts Synthesis, characterization, and application as solvents in Rhodium (I)-catalyzed hydroformylation of 1-octene. Organometallics. 2004. 23, 783-791. 

PyrroldJJ-i -as-triazine.1 This lOa-heteroaromatic system (2) has been synthesized by the base-catalyzed cyclodehydration of pyrrole-2-carboxaldehyde formyl-hydrazone (1) in refluxing xylene in 56 % yield. 

In a base-catalyzed reaction, 1,3,5-triazine serves as a source of the CN unit for the cyclization between the ester function and an adjacent methyl group in 4-methylpyrimidine-5-carboxy-lates. Thus, with sodium hydride, 9 is converted into 2-methyl-4-phenyl-l,4-dihydropyrido-[4,3-d]pyrimidin-5(6//)-one (10).521,522... 

Several 1,3,5-triazine mono- and dialdoximes 5 can be prepared by the base-catalyzed condensation of the corresponding methyl-1,3,5-triazines 4 with alkyl nitrites. The formation of either the mono- or the dialdoxime is dependent on the reaction conditons used. Hydrolysis of the oximes to 1,3,5-triazinecarbaldehydes 6 can only be achieved for 4,6-diaryl-l, 3,5-triazine 2-al-doximes. These aldehydes can also be obtained by reaction of 4,6-diaryl-2-methyl-l,3,5-triazi-nes with sodium nitrite in concentrated sulfuric acid.162... 

Reactions of 1,3,5-triazine (1) with amidines, amidine salts or nitriles which have acidic a-methylcne groups are of great preparative value. The base-catalyzed reactions produce 5-substituted pyrimidin-4-amines 3 (R3 = NH2) in good yield. The corresponding imidate or thioamidate hydrochlorides yield 4-alkoxy- and 4-(alkylsulfanyl)pyrimidines, respectively.24 Some other malonic acid derivatives react in a similar manner as shown below. In these cases, a sodium alkoxide is needed as condensing agent.18,25... 

Masquelin has presented a facile preparation of 2,6-disubstituted triazines 194 through base-catalyzed cyclization of the corresponding thiouronium salts 193 (Scheme 29). 

Highly viscous triazine-based ionic liquids have been recently applied for the rhodium catalyzed hydroformylation of l-octene [179]. Hydroformylation was carried out at 69 bar syngas pressure and total l-octene conversion was achieved... 

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