Urazole synthesis

In contrast to thermal uncatalyzed reactions of /V-acylsulfinylamines with aryl isocyanates which give rise to azoarenes,188 the cobalt or iron carbonyl-catalyzed process gives additionally 3,5-dioxo-l,2,4-triphenyl-1,2,4-triazolidine (Scheme 124).189 The only possible restriction on this simple urazole synthesis would be the expectation that the substituents on the reactants must be the same to prohibit exchange. 

Anhydrous lanthanon nitrates, synthesis 11 Cyanogen, synthesis 12 Allophanyl hydrazide, synthesis 13 Urazole, synthesis 14 Organosilazane compounds, synthesis 16 IV-Nitrosohydroxyla-mine-iV-sulfonates, synthesis 31 Hydroxylamine-O-sul-fonic acid, synthesis 32... 

Analogous reactions are reported for the synthesis of urazoles (1,2,4-triazacyclo-pentandione-3,5), monothiouracoles, and dithiouracoles.11491... 

The treatment of N-aminourazole (38) with two equivalents of BAIB in DMSO results in imidation of the sulfoxide and oxidation of the urazole ring to give the sulfoximine 39 (Scheme 20) [46]. The preparation of 39 from 38 can also be accomplished stepwise, by isolation of the dihydro sulfoximine intermediate and BAIB-oxidation of this compound in acetonitrile. The sulfoximine 39 was not isolated, but was generated in solution and employed for the synthesis of bicyclic diazenes. 

Ethyl allophanate, preparation of, for synthesis of allophanyl hydrazide and urazole, 6 48,... 

Modification of macromolecular material properties by hydrogen bond formation has been demonstrated at the example of thermoreversible networks Stadler modified poly(butadiene) elastomers with urazole groups to introduce hydrogen-bonded cross-links into the system. In fact, thermoreversible cross-linking appeared due to the urazol-urazole molecular recognition, causing intermolecular cross-links [408,467]. The group of Meijer expanded the approach by the synthesis of two... 

This generalization does not extend to l,2,4-triazolidine-3,5-diones both the 1-phenyl-and 4-phenyl-urazoles (89) and (90) can be diacetylated to (91) and (92), respectively, as in Scheme 29 (70JHC821, 66AP44i) the first of these reactions occurs with a yield of 69% while the yield in the second is almost quantitative. Phosgene does not afford carbonyl-ditriazolidines but carbamyl chlorides such as (93) which are useful intermediates in the synthesis of areas and urethanes (74AP504). 

Kolb VM, Dworkin IP, Miller SL. Alternative bases in the RNA world the prebiotic synthesis of urazole and its ribosides. J. Mol. Evol. 1994 38 549-557. 

While exploring the synthesis and chemistry of urazoles, we studied an alternative process starting from carbazate which avoids the handling of the extremely noxious cyanogen chloride. The new synthesis of (IV) is diagrammed in scheme 215 (Ref. 264). 

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. ... 

Urazoles represent a highly functionalized heterocyclic core, the synthesis of which is shown in Scheme 10. In the cases of N,N -diphenylhydrazine and unbranched aliphatic N,N -disubstituted hydrazines 37, carhonylimidazole Wang resin 36 was reacted at room temperature. N,N -Diisopropylhydrazine required elevated temperatures for complete conversion. The intermediate carbazate 38 was coupled to aromatic or aliphatic isocyanates to give the precursor 39 for cychzation. Cyclization was conducted with triethylamine/toluene at 110 °C or vrith KOtBu/ THF at 60 °C (18 h each) to give urazoles. The latter conditions are used especially for sterically crowded residues (e.g., IC = cyclohexyl). Using isothiocyanates in the... 

Bridged Azoalkanes. - The formation of (76) from bicyclobutane has been reported/ together with studies of its thermolysis in solution, its gas-phase pyrolysis, and its photolysis.The synthesis of azoalkanes from the corresponding urazoles by hydrazinolysis (rather than the usual oxidative hydrolysis methods) takes place in good yield [e.g., 70% for (77a)].The resolution and determination of the absolute configuration of an optically active 4,5-diazatwist-4-ene (79), derived from (78), has been achieved. 

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