Urazoles, methylation

Certain facts in the urazole series can also be interpreted in this way. Urazole (17) itself reacts with diazomethane quickly to yield 4-methyl-3-methoxy-l,2,4-triazolin-5-onc (18), which is more slowly converted to l,4-dimethyl-3-methoxy-l,2,4-triazolin-5-one (19). 1-Phenylurazolc gives 4-methyI-3-mcthoxy-l-plicnyl-l,2,4-triazolin-5-one (20) however, 4-phenylurazole yields the 1,2-dimethyl derivative (21). In the case of 4-methylurazole both O- and A"-methylation... 

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>. 

The acid values of a number of urazole derivatives have been measured in DMSO. The H(l)(2) and H(4) protons of urazole in this medium are of comparable acidity and the pAa is 13.1. The N(l) and N(4) phenyl and methyl derivatives are more acidic, both substituent groups having surprisingly similar effects <90JOC5806>. 

Characteristic examples of the use of IR spectra are structural studies on urazoles and triazolinones (66T(S7)213) and triazolinethiones (7UCS(C)ioi6). Tautomeric problems of oxo-hydroxy and thione-thiol systems are simplified by JV-alkylation (73CPBI342). Although earlier views in favour of 0x0 and thio rather than hydroxy and thiol forms have been confirmed, counter-examples have been found 3-hydroxy-2-methyl-5-phenyl-1,2,4-triazole (25) is preferred to the 0x0 tautomer (26) while the isomeric 4-methyl compound (27) follows the general rule (Scheme 9). 

The submitters report a similar yield on a scale three times that illustrated here. This method has been employed for the preparation of the 4-methyl- (100%, m.p. 143° from ethyl acetate), 4-i-butyl- (100%, m.p. 147° from ethyl acetate), and 4-p-nitrophenyl-l-carbethoxysemicarbazide (90%, m.p. 219° from methanol). Because of the impure nature of commercial p-nitrophenyl isocyanate, the produet from that reaction may be contaminated with 2 -nitrophenylurea. It can be used in this impure form for preparing the corresponding urazole, as the contaminant is alkali insoluble. 

Methyl urazol 302 was oxidized into A-methyl triazoline-3,5-dione with tert-buiy hypochlorite. Without isolation, it was then reacted with ( )-penta-2,4-diene-l-ol giving adduct ( )-303 as a racemic mixture. On treatment of ( )-303 with a lipase (R/Novozym 435) in vinyl acetate, 38% of ester (5)-304 (86% ee) and 29% of alcohol (/ )-303 (59% ee) were isolated. Epoxidation of (5 )-304... 

Note also that reaction of methyl-N-chlorocarbonyl-N-methyl carbamate (preparation through phogenation given in section 3-3-4, this volume) is very suitable for the preparation of numerous urazoles. Some examples are presented in table 3-30 (Ref. 265). 

Table 3-30 Use of methyl-NrocarbonyTN-methyl carbamate for the preparation of urazoles.

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 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... 

Dioxy l phenyl benztriazol 26 I 34. 4.5>Dloxy 2urazol 26, 203. l -Naphthyl urazol 26, 203. [Indol (2)] [3-methyl-pyrazol-(4)]-indigo... 

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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