Urazole, 4-substituted

Several TADs have also been studied as low-temperature modifiers of dienic polymers, especially butadiene homo- and copolymers. Isolated double bonds in these polymers react in the same sense as in the ene reaction (Scheme 90) to give urazole-substituted polymers 519 (79MI3). Depend-... 

Triazole has been prepared by the oxidation of substituted 1,2,4-triazoles, by the treatment of urazole with phosphorus pentasulfide, by heating equimolar quantities of formyl-hydrazine and formamide, by removal of the amino function of 4-amino-l,2,4-triazole, by oxidation of l,2,4-triazole-3(5)-thiol with hydrogen peroxide, by decarboxylation of 1,2,4-triazole-3(5)-carboxylic acid, by heating hydrazine salts with form-amide,by rapidly distilling hydrazine hydrate mixed with two molar equivalents of formamide, i by heating N,N -diformyl-hydrazine with excess ammonia in an autoclave at 200° for 24 hours, and by the reaction of 1,3,5-triazine and hydrazine monohydrochloride. ... 

The radical cations of urazole-annelated azoalkanes 65 were generated by pulse radiolysis and the transients characterized spectrally and kinetically by time-resolved optical monitoring. The initial distonic 1,3 radical cations 66 were detected, and the methyl-substituted 66 further deprotonates to radical 67 (Scheme 1) <1997JA10673>. 

Substituted (5R,6A,)-6-(dimethyl(phenyl)silyl)-2-phenyldihydropyrazolo[l,2- ][l,2,4]triazole-l,3(2//,5//)-dione 716, synthesized via the [3+2] annulation of a-substituted allylic silanes 715 with PTAD, were oxidized to the corresponding hydroxy substituted urazoles 717. This work shows that allylsilanes with a single substituent at the allylic carbon undergo exclusive stereoselective [3+2] annulation (Scheme 114) <2007TL6671>. 

Triazoline-3,5-dione 184 underwent an ene reaction with olefins 183 to yield trialkylated allylic urazoles 185, which were further elaborated into allylic amines 186 . DBU has been found to be a mild and convenient base for the alkylation of 1,2,4-triazole with various alkyl halides in the high yielding syntheses of 1-substituted-1,2,4-triazoles <00TL1297>. 

A novel route to synthesize l,3 -triazine-2,4(l//,3//)-diones through the desulfurization of thiocarboamides, such as 1,3-disubstituted 2-thioureas, trisubstituted thioureas and N-substituted thioamides by silver cyanate has been reported <00H(53)929>. Treatment of urazole 23 with one equivalent of sodium hydride under anhydrous conditions, followed by addition of dimethyl sulfate, leads to l,3,5-triazine-2,4-dione 24 in 80% yield . 

Substituted urazoles have also been made by heating the corresponding N,N -disubstituted diamides of hydrazodicar-boxylic acid,9 but the results are difficult to reproduce. 

Phenyl-l,2,4-triazoline-3,5-dione has been prepared by oxidizing 4-phenylurazole with lead dioxide,7 and with ammoni-acal silver nitrate followed by an ethereal solution of iodine.8 The yields are low for both methods. 4-Substituted triazoline-diones can also be made by oxidation of the corresponding urazole with fuming nitric acid9 or dinitrogen tetroxide.10 Oxidation by <-butyl hypochlorite in acetone solution has also been described 1112 it, however, yields an unstable product, even after sublimation. Either dioxane12 or ethyl acetate are preferred as solvents for the reaction, since the product is obtained in a stable form. The latter solvent is superior since... 

New crosslinked elastomers may be formed by self-aggregation of substituted functional units able to form directed hydrogen-bonds. 1,4-PB has been randomly substituted with about 4 mol% urazole units [94], The urazole units form hydrogen-bonded supramolecular, plate-like aggregates which act as effective crosslinking zones, thus creating a thermoplastic elastomer [95, 96, 97]. The system is deuterated either in the PB backbone or in the urazole units, which allows to investigate the molecular dynamics in... 

Although l,2,4-triazoline-3,5-dione is unstable even at 0 °C, it can be reacted with dienes in situ when formed by the oxidation of urazole (5) with dinitrogen tetroxide (73TL2101). A-Substituted derivatives are more convenient to use. 

Another situation in which the chemically robust nature of the 4-methyI-l, 2,4-triazole-3,5-dione adducts has been exploited is in the synthesis of bicyclobutane derivatives.Addition of 4-methyl-l,2,4-triazole-3,5-dione to bicyclo[1.1.0]butane gave the urazole 20, which was converted to 2,3-diazabicyclo[2.1.1]hex-2-ene and by thermolysis or photolysis back to bi-cyclo[1.1.0]butane. While this is not in itself a useful synthetic sequence, the urazole intermediates in such a sequence can be chemically modified in ways that would be impossible for the bicyclobutanes themselves. Hence for the adduct 21 of dimethyl bicyclo[1.1.0]butane-l,3-dicarboxylate, the ester groups can be modified into ethyl, vinyl, substituted vinyl, hydroxymethyl, bromo and other substituents and this was used to prepare, for example, 1,3-divinylbicyclo[1.1.0]butane (22) and l-ethyl-3-vinylbicyclo[1.1.0]butane. ... 

The reaction of 3-substituted 1,2-diphenylcyclopropenes with 4-phenyl-4//-l,2,4-triazole-3,5-dione gave urazoles, possibly via the formation of a spiro[2-azabicyclo[1.1.0]butane-2,T-l,2,4-triazole] and subsequent ring opening. 

The same trend in the electronic effects is observed experimentally for the urazole-bridged 4,5-diazacyclopentane-l,3-diyl triplet diradicals 7 (Table 5), which were chosen to probe for the effect of heteroatom substitution on the D parameter. Substitution of a phenyl by a methyl group in 7d also results in an increased D value in 7g, but is less effective (18%) as seen in the carbocyclic derivatives. These results are in line with the earlier reported [17] D values of iV-phenylurazole-bridged cyclopentene-1,3-diyl triplet diradicals 7a-c (cf. Table 1). As for the carbocyclic diradicals, the electronic substituent effects are reproduced in the diradicals 7e and f not only qualitatively but quantitatively (Table 5). For example, the spin-accepting p-CN substituent in the triplet diradical 7e reduces while the spin-donating... 

Substituted (R = Ph, Me, PhCH2) 3,6-dihydro-6-oxo-l-pyrimidinium-4-olates (295) treated with TADs provide products of 1,4-dipolar cycloaddition (296) (Scheme 51). In contrast, 5-unsubstituted derivative 295 (R = H) undergoes nucleophilic substitution to give the corresponding urazole (85CB4567). 

This method of preparation of ylides from the corresponding triazolinedi-ones is limited in its synthetic utility. Oxidation of suitable urazolyl compounds seems to be a much more versatile entry to this class of highly reactive dipolar compounds. Starting substituted urazoles are often readily available by simple nucleophilic substitution reactions of urazoles with suitable alkyl halides. As is evident from the preceding sections, many other substituted urazoles can be prepared by the ene-type reaction of TADs, by the reaction of TADs with ketones, or by their electrophilic aromatic substitution reactions. Oxidation of these urazoles, e.g., 501, 428, 504, and 506, can be effected with tert-butyl hypochlorite, or, in some cases, excess PTAD can be used. Various approaches and utilization of this synthetic strategy are best seen in the following examples. 

Breton found the photoinduced aromatic substitution reactions of substituted benzenes with N-methyl-l,2,4-triazoline-3,5-dione (127) to give 1-arylurazoles (128). In the cases of methyl-substituted benzene derivatives (129), both 1-arylurazoles (131) and benzylated urazoles (130) were obtained. Electron-donating benzene derivatives such as... 

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