1,2,3 triazole Dimroth rearrangement

In the case of some fused [l,2,4]triazoles, Dimroth rearrangements to the appropriate isomeric ring systems have been observed. Thus formations of (16) from (15) <84JCS(Pl)993>, (20) from (21) <90JCS(P2)1943>, and (32) from (30) <82JHC1345> have been reported. These transformations are also discussed in the respective sections on synthesis. 

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... 

Assignment of the l,2,4-triazolo[l,5-c]pyrimidine structures to the products obtained from the previously described cyclizations and not the alternative [4,3-c] structures has been rationalized and corroborated on the basis of (a) preference of cyclization at the more nucleophilic triazole ring N2 rather than at its less nucleophilic N4 (65JOC3601 88JMC1014), (b) inability of the obtained products to undergo acid- or base-catalyzed Dimroth rearrangement, a property characteristic of the thermodynamically less stable [4,3-c] isomers (91JMC281), (c) comparison with unequivocally prepared... 

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). 

Azide 367 is prepared from 4-r -butyl-2-nitroaniline in 76% yield by its diazotization followed by treatment with sodium azide. In a 1,3-dipolar cycloaddition with cyanoacetamide, azide 367 is converted to triazole 368 that without separation is directly subjected to Dimroth rearrangement to give derivative 369 in 46% yield. Reduction of the nitro group provides ortfc-phenylenediamine 371 in 91% yield <2000EJM715>. Cyclocondensation of diamine 371 with phosgene furnishes benzimidazol-2-one 370 in 39% yield, whereas its reaction with sodium nitrite in 18% HC1 leads to benzotriazole derivative 372, which is isolated in 66% yield (Scheme 59). Products 370 and 372 exhibit potassium channel activating ability <2001FA841>. 

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>. 

Heating of a solution of 5-ethyl-3-phenyl-l,3,4-thiadiazol-2(377)-imine 85 in aq. NaOH to 80°C for 5h gave the 5-ethyl-2,3-dihydro-2-phenyl-l/7-l,2,4-triazole-3-thione 86 via Dimroth rearrangement (Scheme 7) <2002HCA1883>. Nucleophilic attack of the hydroxide on the electrophilic C-5 resulted in ring opening and, after rotation around the C(2)-N(3) bond and subsequent recyclization, triazole thione 86 formed. 

The aroyl-substituted heterocyclic ketene aminals 482 react with 4-chlorophenyl azide to give polysubstituted 1,2,3-triazoles 483 and imidazo[ 1. Z-r 1.2,4]triazoles 39 (Equation 112) <2000HAC387>. Polysubstituted 1,2,4-triazoles are formed by the nucleophilic attack of the ct-carbon of the azide. Then, through the cyclocondensation and aromatization sequences, the fused heterocycles resulted by a 1,3-dipolar addition at first, and then through a Dimroth rearrangement and deamination of chloroaniline <1992JOC184>. 

The best-documented ring transformation of the systems presented in this chapter is the Dimroth rearrangement of fused [l,2,4]triazoles. Such transformations were discussed in CHEC-II(1996) <1996CHEC-II(8)421> and, also, several novel cases have also been discovered. These are depicted in Scheme 15. 

It is important to note that besides these synthetic pathways a very important access to [ 1,2,4]triazolo[ 1,5 z] pyrimidine derivatives is the Dimroth rearrangement of [l,2,4]triazolo[4,3-c]pyrimidine compounds. This type of ring transformation is specifically discussed in Section 11.16.5.2 these possibilities are also reviewed in Section 11.16.7. As these isomerizations always take place into the direction of the [l,2,4]triazolo[l,5-c]pyrimidine ring, in several studies only these products are described without special (or any) note of the primarily formed [l,2,4]triazolo[4,3-c]pyrim-idine ring. Table 17 contains the stmctures of some [l,2,4]triazolopyrimidines and benzologues with a fusion site of the triazole ring that have been formed via transformation of the isomeric [ 1,2,4] triazolo[4,3-f]-pyrimidine compounds with or without isolation of these intermediates. 

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). 

Imines derived from ketones with an a-methylene group can react via their enamine tautomers, and mixtures of triazoles are also isolated from these systems. The triazoline adducts of the enamine tautomers are aromatized by treating with acid, and in these conditions the triazoline appears to undergo a Dimroth rearrangement before elimination of the amine, because two triazoles are obtained, one of which has... 

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°). 

Ring-chain equilibria of 1,2,3-triazoles and benzotriazoles with the isomeric a-diazo imines result in the well-known Dimroth rearrangement (see Section 4.01.4.1.1). 

Junjappa and co-workers (9) reported the cycloaddition of sodium azide to the polarized ketene-(5,5)-acetal 33 to give the tiiazole 35 they also reported an intermolecular cycloaddition of tosyl azide 37 with the enamine 36 to give an unstable triazoline intermediate 38. Ring opening 38 followed by a Dimroth rearrangement afforded the triazole 41 (Scheme 9.9). 

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. 

Type B syntheses starting from HPs require a Dimroth rearrangement. By contrast, in the following reaction paths, the 1,3 orientation of two nitrogen atoms needed to form the triazole ring of the TP is preformed in the pyrimidine precursor. 

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. 

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