4-Amino-1,2,3-triazoles Dimroth rearrangement

Triazole, 5-amino-1,4-diphenyl-photo-Dimroth rearrangement, 5, 697... 

Amino-l,2,4-triazole undergoes a cyclocondensation with 3-etlioxyacrolein (7) to form 1,2,4-triazolo[l,5-a]pyrimidine (3) or its [4,3-u] isomer (5), according to whether it reacts as IH or 4H tautomer 2 or 4. Moreover, the pyrimidines 3 and 5 can interconvert by a Dimroth rearrangement. Since the H NMR spectrum 30a does not enable a clear distinction to be made AMX systems for... 

Diazotization of 5-amino[l, 2,3]triazole 692 afforded (88BSB179) triaz-olo[l, 5-i>][l, 2,4]triazine 694 as a result of a Dimroth rearrangement of the initially formed isomeric structure triazolo[5,l-c][l,2,4]triazine 693. Molecular structure of 694 was determined by single X-ray diffraction (Scheme 146). 

The 1,3-dipolar cycloaddition of azido-l,2,5-oxadiazoles (azidofurazans) to dicarbonyl compounds has been studied and a new procedure for the synthesis of (l,2,3-triazol-l-yl)-l,2,5-oxadiazoles was proposed <2002MC159>. The cycloaddition of 4-amino-3-azido-l,2,5-oxadiazole 168 to nitriles with activated methylene groups has been studied, and 3-amino-4-(5-amino-l/7-l,2,3-triazol-l-yl)-l,2,5-oxadiazoles 169 and the products of their Dimroth rearrangement 170 have been synthesized <2004MC76>. 

It was concluded that the rearrangement follows the same pattern as described in Scheme IV.5 for the Dimroth rearrangement of 5-amino-l, 2,3-triazoles, i.e., the involvement of the intermediacy of a diazoimine (Scheme IV.46). 

Examples of the Dimroth rearrangement (Section IV, F) include several s3mtheses of monocyclic triazoles from other heterocyclic systems (cf. Scheme 25). Triazole-5-thiols can be prepared by treatment of 5-amino-l,2,3-thiadiazoles with bases.A similar base-induced rearrangement of sydnoneimines provides a synthesis of 4-hydroxy-triazoles. ... 

Heating l-acetamido-4-phenyl-l,2,3-triazole with hydrochloric acid is claimed to give5-amino-4-phenyl-l,2,3-triazole (m.p. 125°) theanalogy is incorrectly drawn between this rearrangement and a Dimroth rearrangement. The product obtained may in fact be the unrearranged l-amino-4-phenyl-1,2,3-triazole (reported m.p. 124°). 

For the retro-Dimroth rearrangement of a TP, apparently only one example has been found (70JPR254) 5-Amino-6-cyano-TP (24) under the influence of the unusual rearranging agent concentrated sulfuric acid leads to [4,3-a] derivative 25 (Scheme 12). The triazole ring is believed to be polyprotonated in this medium and to have its most nucleophilic site at N-4. 

Synthesis of this ring may be achieved by the construction of one of the heterocycles followed by using it as a basis to build the other ring onto it or by the Dimroth rearrangement of l,2,4-triazolo[4,3-a]pyrimidines. 1,2-Diaminopyrimidines are general precursors, and they can be generated from 1-amino or 2-aminopyrimidines. The 3- and 5-amino-l,2,4-triazoles are alternative precursors that can act as a source of three carbons to complete the pyrimidine ring. 

Dimroth rearrangement also occurs between the 5-mercapto-l,2,3-triazoles (109) and the 5-amino-l,2,3-thiadiazoles (110). If the thiadiazoles (110) are heated in basic solvents they are converted into the triazoles, whereas the reverse reaction is observed in acidic media (67LA(710)118, 69CB417, 72ACS1243). Thermal equilibria of thiadiazoles and triazoles, with both isomers present, have been reported (62Acs(B)1800, 66CB1618). 

Besides ring-chain tautomerism (Section 4.11.4.1.2(0) and the Dimroth rearrangement (Section 4.11.4.1.2(iii)) cleavage reactions of some amino-, azido and diazo-methyltriazoles have been reported. Thus, 5-azido-l,4-diphenyl-l,2,3-triazole (121) proved to be unusually labile above 50 °C. Nitrogen is evolved with the formation of a conjugated nitrile (122) (64JA2025, 70JOC2215). Similarly the diazomethyltriazole (123) decomposes to (124). Both reactions can be explained in terms of concerted processes. 

Another synthetic pathway recently used is the cyclization of linear triazenes, like (224), which in aprotic media with Lewis base catal) is yield 5-amino-1-ary 1-1,2,3-triazoles (225). However, in protic media Dimroth rearrangement affords the isomeric 5-(arylamino)-l,2,3-triazoles (226) (70JOC2215, 81JOC856). The 2-tetrazene (227) gives methyl l-benzyl-1,2,3-triazolecarboxylate (228) by photochemically induced homol) is of a single N—N bond (81TL227). 

Methylamino-8-azapurine uniquely followed a more complex path. A simultaneous Dimroth rearrangement to 6-amino-9-methyl-8-azapurine (Section C,2) allowed two isomeric amidinotriazoles to be formed, one from each 8-azapurine. 6-Amino-8-azapurine, when set aside in cupric chloride solution, produced the following complex tetrachlorobis-2-[(4-amino-5-carboxamidinium)-l,2,3-triazole]copper +, the structure of which was verified by single-crystal X-ray work. ... 

Ultraviolet spectra have proved useful in following Dimroth rearrangements (Section III,D) where a 3-alkyl (or 3-aryl) group becomes a 4-alkylamino (or 4-arylamino) group. Four such pairs can be seen in Table II, e.g., 4-amino-3-benzyl- and 4-benzylamino-1,2,3-triazoles. In each case, a bathochromic shift of about 10 nm occurs. H-NMR spectra are also useful in following such reactions (see Section II,D). 

Irradiation of 4-amino-3,5-diphenyl-1,2,3-triazole, in ethanol with a high-pressure mercury lamp for 40 hr, gave an equilibrium mixture of starting material and the Dimroth-rearrangement product, 4-anilino-5-phenyl-l,2,3-triazole (35% yield), separated by thin-layer chromatography. When the product was similarly irradiated, the equilibrium was reestablished (see also... 

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