1.2.3- Triazoles transformation

In the indazole series an example of a type (c) reaction (Figure 25) has been described utilizing a 1,3-dipole instead of a diene (Scheme 32) (76H(4)1655). The cycloadduct (351) is transformed into the triazole (352) on reaction with hydrochloric acid. 

Three skeleton atoms of a hetero-l,3-diene are incorporated into a five-membered ring system on reaction with 1,2 [n,n] compounds (e.g., hydrazines, reaction type 4, equation 10). On further heating in the presence of azobisiso-butyronitrile (AIBN), the bis(trifluoromethyl)-substituted 1,2,4-triazolines are transformed into 5-tnfluoromethyl-l,2,4-triazoles in high yield [t02 (equation 22). 

The conversion of a 4-arylazo-5-oxazolone into a 1,2,4-triazole by reaction with a Grignard reagent is mentioned in Section II, B, 3. In HiTnilar fashion, the rearrangement of compound 30 to derivatives of 3-carboxy-l,5-diphenyl-lfl -l,2,4-triazoles (40) proceeds readily in the presence of strong nucleophiles [Eq. (26)]. This transformation undoubtedly occurs by ring opening and dehydrative cychzation, and, indeed, the acyclic amide and hydrazide 41 have been isolated. ... 

The condensed l//-l,2-diazepines 12 are transformed into the 3//-tautomers 24 by reduction with lithium aluminum hydride to give 23, followed by dehydrogenation with 4-phenyl-4//-1,2,4-triazole-3,5-dione.146... 

As early as 2001, Furstner and co-workers reported the preparation and full characterisation of complex 45 [29] (Fig. 3.17), which incorporates a triazole-based iV-heterocycle that was previously isolated by Enders [59]. A few years later, complex 45 was also prepared using another pathway by Grabbs [60]. When tested in the standard transformation from 5 to 6, complex 45 provided a snrprisingly high yield of 80% in just 2 h. However, higher conversion npon prolonging the reaction time was not observed. Further studies revealed that complex 45 was unstable in... 

Ref. [152] discusses the transformation of a dinucleoside pyrophosphate into a reactive azolide with an azole (e.g., 3-nitro-1,2,4-triazole or tetrazole). With quinoline-8-sulfonyl chloride the concomitantly formed phosphordiester can be converted back to the dinucleoside pyrophosphate (see scheme on the next page). 

Amino 4-oxo 4//-pyrimido[l,2-4]pyridazin-3-diazonium tetrafluoroborates 73 underwent ring transformation into l-(pyridazin-3-yl)-l//-l,2,3-triazole-4-carboxylates 74 on heating in dry MeOH. Yields dropped drastically when EtOH, instead of MeOH, was used as solvent (Equation 6) <2002ARK143>. 

The mesoionic tetrazole dehydrodithizone is transformed by iron penta-carbonyl into 4-phenyl-2-phenylazo-A2-l,3,4-thiadiazolin-5-one, presumably by a mechanism of ring opening, complexation, carbonyl insertion and subsequent ring closure (Scheme 128).193 Unfortunately, analogous processes do not occur on other mesoionic compounds in the 1,2,3-oxadiazole, s-triazole or tetrazole series, and the scope of this unusual carbonylation is probably limited. 

Conversion of other heterocyclic systems into pyridazines has also been used, for example the reaction of 3-aminopyrone 9 with hydrazine, followed by oxidative aromatisation <06T9718> and the more unusual utilisation of a 1,2,4-triazole 10 as the source of the N-N unit <06T8966>. In this latter transformation, the intermediate quaternary salt 11 was isolable. An even more unusual example was the reaction of the diazetidine 12 with enolates <06S2885>. 

Computational methods were employed to predict molecular vibrations in 3-mercato-l,2,4-triazole 18 and 3,5-diamino-1,2,4-triazole 19 in order to fully assign the Fourier transform infrared (FTIR) and FT-Raman spectra of these molecules <2004SAA709, 2005SAA261>. 

In a similar fashion, 1,3,4-oxadiazole 210 was transformed into 1,3,4-triazole 211 (Equation 66) <2004BML6057>. 

It was shown that furoxans can be transformed to 1,2,3-triazoles. Thus, 4-acetylamino-3-arylazo-l,2,5-oxadiazole 2-oxides undergo two successive (cascade) mononuclear heterocyclic rearrangements in an aqueous basic medium with the formation of 4-acetylamino-2-aryl-5-nitro-2/7-l,2,3-triazoles (Equation 12) <2001MC230>, or 3,3 -disubsti-tuted 4,4 -azo-l,2,5-oxadiazole 2-oxides were found to undergo a rearrangement into 2-(furoxan-4-yl)-4-nitro-2//-1,2,3-triazole 1-oxides on heating in pertrifluoroacetic or peracetic acids (Equation 13) <2003MC272>. 

The reaction of compound 376 with hydrazine gives product 377 that has been transformed into similar triazoles 378, after reaction with carbon disulfide in the presence of alcoholic potassium hydroxide, benzoic acid in the presence of phosphoms oxychloride, or 3-[bis-(methylthiomethylene)]pentan-2,4-dione and l,l-dicyano-2,2-dimethylthioethylene, in refluxing -butanol (Scheme 40) (Table 55) <2000FES641>. 

Triazolotriazepinones 475, obtained by reaction of 4,5-diamino-3-aryloxymethyl-l,2,4-triazoles 474, on heating with acetic anhydride undergo ring contraction reaction to yield l-acetyl-3-aryloxymethyl-6-methyl-pyrazolo[5,l-f][ 1,2,4]triazoles 476 (Scheme 54) <2003IJC(B)2054>. This type of transformation has been previously documented by other authors <1974JHC751>. 

Triazolo[4,3-7 ]pyridazinc-6(5//)-one-3(2//)-thiones 309 undergo an unprecedented ring transformation on treatment with dimethyl acetylenedicarboxylate in DMF, resulting in a new method for the synthesis of thiazolo[2,3-c][l,2,4]triazole derivatives, which is strongly dependent on the reaction temperature and the... 

Several polyheterocyclic compounds containing a condensed 1,2,4-triazole nucleus, such as 3,5-disubstituted thiazolo [2,3-r][ 1,2,4] triazoles, are thermostabilizers for polypropylene and polycaproamide <2003MI2>. Triazolo[3,4-A][l,3]benzothiazoledicarbonitrile derivatives are used to prepare hexazocyclanes-fluorophores as active media for liquid and solid lasers, scintillators, and for transformation of short-wave radiation to long-wave radiation <2004RUP2238276>. 

On treatment with phosphorus pentasulfide, 4-amino-5-thio-477-[l,2,4]triazoles 86 are converted into 6-aryl-3-(2-aminophenyl)[l,2,4]triazolo[3,4-4][l,3,4]thiadiazoles 3. This transformation is presumed to involve three steps first, the transformation of the amide into the thioamide second, transfer of the thioaroyl group from the phenylamino side chain to the iV-amino group of the triazole ring and, finally, cyclodehydrosulfurization leading to 3 (Equation 21) <1989LA1055>. 

X-Ray elucidation provided a final proof for the structure elucidation of 8-(4-chlorophenyl)-8-hydroxy-5-methyl-8/f-[l,4]thiazino[3,4-H[l,2,4]oxadiazol-3-one 49, which was obtained as a product of ring-transformation reaction <1997J(P2)2407>. This analysis revealed that the oxadiazole ring is planar, whereas the thiazine ring is in a distorted half-chair conformation with a displacement asymmetry parameter AC2 (S—G(3)) = 0.031. The structure analysis represents the first X-ray elucidation of a [l,4]thiazine ring fused to a [l,2,4]triazole moiety. 

Basic hydrolysis of the [l,2,4]triazolo[5,l-3][l,3]thiazine derivative 77 was described to yield triazole-thione 78, the reaction proceeding in 59% yield <2005ZOR1092>. Related partially saturated triazolothiazines 79 were also subjected to ring-opening reaction aqueous hydrolysis afforded the acid 80 <2004KGS1256>, whereas reaction of 79 with hydrazine hydrate yielded the acid hydrazine 81 <2004ZOR260>. Both transformations took place in high yields. 

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. 

Two examples for acylation of ring nitrogen atom are shown in Scheme 22. Reaction of 180 with various esters was decribed <2000MOL1210>. The transformations took place on the N-2 triazole nitrogen atom to give 181 in poor to medium yields (Scheme 22). 

Fathalla et al. reported that some [l,2,4]triazolo[4,3- ]quinazoles can be subjected to various transformations involving the triazole nitrogen atom <2000MOL1210>. Thus, treatment of 186 with formaldehyde and pyrrolidine... 

Ring closure of the cyano group containing aniline (312) to 313 <1994T7019, 1996J(P1)225> followed the same pathway as that with the oxazine analogue discussed earlier with transformation of 291 into 292. Formation of the fused triazole 315 from 314 was also reported <1994FA245>. 

Scheme 47 contains syntheses of [l,2,4]triazolo[4,3- ]pyridazine derivatives by ring closure of the triazole moiety. Kozhevnikov et al. reported <2005MC31> an interesting ring transformation treatment of the... 

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