Triazol-3-imines

3-Triazol-4-imines (Anhydro-4-amino-l,2,3-triazolium Hydroxides) (193) 

The A-methyl-JV -arylazoaminoacetonitriles (194) and hydrogen chloride in ether yield the 1,2,3-triazolium chlorides (195). These salts (195) and base did not give the corresponding meso-ionic compounds (193, R1 = Me, R2 = Ar, R3 = R4 = H), but the corresponding )V-acetyl derivatives (193, R1 = Me, R2 = Ar, R3 = H, R4 = Ac) were produced either from the nitriles (194) and acetyl chloride or from the 1,2,3-triazolium chlorides (195) and acetic anhydride, followed by treatment with ammonium hydroxide.127 

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The reaction of N-aminoazonium salts with aliphatic and aromatic aldehydes in the absence of base gives the Schiff base type compounds 28.151,153-156 Some aliphatic ketones also react with N-aminoazonium salts.40,155 Hexane-2,5-dione reacts with N-aminopyridinium perchlorate to give l-(l -pyrrolyl)pyridinium cation 29 together with some of the bisper-chlorate 30.157 Certain esters such as diethyl malonate and ethyl cyano-acetate react with N-aminopyridinium salts in the presence of base to give the corresponding N-acylimines 31.48 However, the reaction of ethyl aceto-acetate and acetylacetone with N-aminoazonium salts in the presence of base gives 1,3-dipolar cycloaddition products (Section IV,C,1).36,154,158 The reaction of ethyl acetoacetate with 1-alkyl-l,2,4-triazole 4-imine affords zwitterionic triazolo[4,3-/>]pyridazines 32.139,159... 

Dipolar cycloaddition of 1-alkylbenzimidazole IV-imines with dimethyl acetylenedicarboxylate results in the formation of the ring-opened pyrazole derivative 79 (Eq. 31).151,203 1-Methyl-l,2,4-triazole 4-imine also reacts in a similar manner to give a pyrazole derivative (80),204 but Summers and Elguero obtained a rather unusual product (81) from the same reac-... 

Alkyl-1,2,4-triazole 4-imines can be also prepared from azides and 1-alkyl-1,2,4-triazoles.87 For instance, the IV-imine 53 is produced when acetyl azide, which under these conditions gives acetyl nitrene,89 is irradiated in the presence of 1-benzyl-s-triazole. 

Triazole 4-imine, as a representative five-membered ring iV-imine, possesses canonical forms 75-78 (excluding quadrupolar structures). 

Apart from the pyridine A-imines,17 19 67 70 71 NMR spectra have been described only for the 1,2,4-triazole 4-imines.80-83 87 The differences in electron density between C-3 and C-5 are reflected in the chemical shifts of the corresponding protons see the NMR spectra of the A-imine 8487 (Scheme 7). The difference between the values for H-3 and H-5 is 1.1 ppm, the same as that of the quaternary acylamino salt 83. 

A-imines of five-membered heterocycles also possess relatively long wavelength transitions compared with those of the parent hetero-cycles.74 80 82 - 87-93 Thus, in protic solvents the absorption maxima for 1,2,4-triazole 4-imines are situated at 2.r>0 nm, whereas the corresponding triazoles absorb at 210 nm. 

The dipolar character of A-imines renders the UV transitions strongly solvent-dependent. For all compounds investigated hitherto the long-wavelength absorption band possesses a negative solvatochromism (see Table III and Dimroth et aZ.38 and Becker et aZ.82). The molar transition energies of pyridine A-arylimines38123 and 1,2,4-triazole 4-imines,82 124 derived from the absorption frequencies, correlate well with the empirical solvent parameters ET, Z, and S correlation with the parameters K, R, and 5 (see Fowler et aZ.126) are poor. 

These experimental results support the equilibria for s-triazole 4-imines of Scheme 12. Further evidence is the fact that the iV-imines react with elemental sulfur without a catalyst82 87 (see also Section IV,C). 

The C-H acidity is also the cause of the reaction of 1,2,4-triazole 4-imines with elemental sulfur [Eq. (12)]82-87 (see Section III,F). It is not clear whether this reaction is an electrophilic substitution or whether it proceeds via an intermediate ylid/carbene (94/95). 

Heterocyclic N-imines contain a quaternary azomethine group which can be attacked by hydroxyl ions, leading to ring-opening. Such reactivity is strongly dependent on the heterocycle. For instance, pyridine N-imines are rather stable to bases17 69 whereas the 1,2,4-triazole 4-imines react very easily.80 82-90 137 In this reaction, the open-chain formamide 96 is... 

Besides being useful precursors to pyrroles pyridine-2-ones -4-ones, -4-thiones. and -4-imines 4-alkylidene-dihydropyridines thiophenes 1,2,4-triazoles thiapyrane-2-thiones, isoquinoline-3-ones isoben-zothiophenes and 4-mercaptoimidazolium hydroxide inner salts, mesoionic thiazoles are potentially useful in the construction of molecules with herbicidic (39). central nerve stimulating, and antiinflammatory properties (40,41). Application in dye synthesis has likewise been reported (42). 

Nitron (4.5-Dihvdro-l, 4-diphenyl-3,5-phenyl-imine-1,2,4-triazole, or l,4-Diphenyl-3,5-endo-anilino-4,5-dihydro-l, 2,4-triazole). N C(NFh>2.CH.N.Ph, C20H16N4, mw 312.36 ... 

More recently, Williams has described the one pot synthesis of 2-substituted oxazoles 11 by the thermolysis of triazole amides 9 the reaction does not proceed photo-chemically.<92TL1033> Although the reaction does not involve addition to a nitrile, it is an interesting application of a diazo compound since the proposed zwitterionic intermediate 10 is a resonance form of a diazo imine, so formally the reaction may be thought of as a thermal decomposition of a diazo imine (Scheme 6). 

The photoelimination of carbon dioxide from esters and lactones is a process that has been the subject of detailed investigations. Discussion here is limited to nitrogen containing systems. 3,4-Diphenylsydnone (464), on irradiation in benzene, is converted via the nitrile imine 465 into 2,4,5-triphenyl-1,2,3-triazole (466)388 initial bond formation between N-2 and C-4 followed by loss of carbon dioxide to give the diazirine 467 is proposed to account for the formation of the nitrile imine. Nitrile imines generated in this way have been trapped with alkenes and alkynes to give pyrazoles389... 

Highly functionalized tetraaryl-4,5-dihydro-l,2,4-triazoles 118a-y have been prepared on a soluble polymer support (PEG4000) from the cycloaddition of diarylimines with a nitrile imine, prepared in situ from the arylhydra-zone 119. The triazole products are highly fluorescent and several have reasonable fluorescence quantum yields (Scheme 8 and Table 19) <2005S3535>. 

Fluorinated triazole derivatives have been prepared by a somewhat deceptive route that starts with imine perfluoro(5-aza-4-nonene) 140 reaction of 140 with aromatic hydrazines gives 1,2,4-triazoles 141a-g in good yields (Equation 44 and Table 27) <2001RJ01621, 2001ZOR1693>. 

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 reaction of phenylazoalkenes 424 with an excess of potassium thiocyanate in acetic acid produces the cycloadducts 425 that undergo further [3+2]-cycloaddition reaction with thiocyanic acid at the azomethine imine function giving rise to the bicyclic product imidazo[l,5-3][triazole]-2,5-dithiones 41 (Equation 87) <1998SL786>. 

Concerning the transformation of substituents, a special note should be made on a series of ring-closure reactions carried out on the side chain of some [l,2,4]triazolo[4,3-r]benzo[l,2,3]triazines published by Moustafa <2001SC97>. The results are summarized in Scheme 18. This scheme shows that by transformation of the R group attached to the sulfur atom of derivative 97 a fairly large set of cyclic products - involving thiazolidone 97a, [l,2,4]triazole 97b, coumarone and its imine 97c and 97d, respectively, benzoxazylpyrane, 97e, thiophene 97f, and cyclopenta- or cyclohexa-fused protected pyrone 97g substituents - have been obtained. 

The formation of cyclic nitrones (150) from pericyclic mechanism. Kinetic and computational studies have provided evidence for the involvement of a novel pseudo-pericyclic electrocyclization in the conversion of o-vinylphenyl isocyanates into quinolin-2-ones. " Such reactions have also provided evidence of torquoselectivity in a 6jt system. Hash vacuum thermolysis of triazoles (151) has been found to afford dihydroquinolines (155), presumably by generation of a-oxoketenimines (152) which can undergo a [1,5]-hydrogen shift to the o-quinoid imines (153)7(154) and subsequent electrocyclization (see Scheme 57). 

It is known that 1//-1,2,3-triazoles can exist in equilibrium with diazo-imines. In the conversion of 1 into 2 as intermediate the diazo-imine 3 can... 

Triazoles have also been obtained when the carbon atom adjacent to the activated methylene group carries a nitrogen function (i.e., amides, nitriles, amidines, and imines - ). In many of these cases it is impossible to decide, without N-labeling experiments, whether the third nitrogen of the triazole ring is derived from the toluene-p-sulfonyl azide or from the activated methylene compound. With amides, amidines, and nitriles, the first possibility seems more reasonable, but with imines, the third nitrogen is that of the imino group (Scheme... 

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... 

Oxidation of a-diketone hydrazone imines with cuprammonium salts gives 2/f-triazoles. With substituted imines (using W-bromosuccin-imide as oxidant) 1,2-disubstituted triazolium salts are obtained (Scheme 33). ... 

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). 

The vapor-phase pyrolysis of 4-hydroxy-1,2,3-triazole and its iV-methyl derivative affords methan-imine and its A-methyl analog. Analysis of the reaction path by the MNDO method shows the presence of two stable or metastable isomers, (liif)-4-hydroxy-l,2,3-triazole and its ketone protomer <89NJC551>. 4-Diazo-1,2,3-triazoles (122) thermolyze or photolyze in benzene to 4//-l,2,3-tri-azolylidenes (123) which convert benzene to 4-phenyl-1,2,3-triazoles and/or isomerize to a-diazo-nitriles (124). Intermediates (124) react with benzene via a carbene to give addition, ring expansion or substitution products (Scheme 17) <82TL5115>. The similar thermolysis of diazotriazoles in substituted benzene gives complex mixtures in which all of the components are sometimes impossible to isolate and identify <90AHC(48)65>. 

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