4.5- Dibromo-1,2,3-triazole

The direct lithiation of a 2-substituted 1,2,3-triazole has not been reported. Halogen-metal exchange of 4,5-dibromotriazole with n-butyllithium at — 80 °C occurs smoothly and the subsequent reaction of the lithium intermediate (244) with various electrophiles except aldehydes gives the 4-bromo-5-substituted triazoles (245) (Scheme 46). The corresponding 1-substituted 4,5-dibromo-1,2,3-triazole undergoes a similar reaction at the 5-position . 

The selective formation of N-2 substituted traizoles has been recently reported. The alkylation of 4,5-dibromotriazole with ethylbromide produces the N-2 alkylated product in an 87 13 ratioThe dibromo-triazole is then readily converted into the monobromo-triazole. 

Halogenation of w-triazole and several monomethyl and dimethyl derivatives has been studied.Bromination of v-triazole gives the 4,5-dibromo derivative with an excess of sodium hypobromite, a 1,4,5-tribromo derivative can also be isolated. Attempted chlorination gave the hydrochloride salt instead, although 1-methyltriazole gives a 4-chloro derivative. A 1-iodo derivative, which rearranges on heating to the 4-isomer, is obtained with iodine. 

Aryl-l,l-dibromo-2,3-diazabutadienes (223)145 and the JV-amino-amidine (219, R1 = Me, R2 = R3 = Ph) yield 1,3,4-triazolium bromides (220, R1 = Me, R2 = R3 = Ph, R4 = H, R5 = N=CHAr), which with ammonia in chloroform solution give novel derivatives (224) of meso-ionic l,2,4-triazol-3-imines (216). These compounds are of interest in that they belong to a new type of meso-ionic heterocycle in which the exocyclic substituent f (see Table I) is a stabilized carbanionoid residue,... 

The synthesis of 3,5-dibromo-l-(thietan-3-yl)-l,2,4-triazole 135 was performed by the reaction of 2-chloro-methylthiirane 99 with 3,5-dibromo-l,2,4-triazole yielding the product in 50% <2005RJ01847> (Equation 38). 

Halo-l-methyl-l,2,3-triazoles undergo substitution reactions with amines, but the 4-halo analogues do not. 5-Chloro-l,4-diphenyl-l,2,3-triazole with sodium cyanide in DMSO gives the cyano derivative. 1-Substituted 3-chloro-and 5-chloro-1,2,4-triazoles both react with amines, and alcohols <2006T2677> but selectivity is illustrated by the reaction of 1-benzyl-3,5-dibromo-1,2,4-triazole with CsF only at C(5) <1998S1357>. 

The reaction of sodium azide with l-bromo-l-nitro-2-arylethenes takes place by a formal 1,3-cycloaddition Scheme leading to 4(5)-aryl-5(4)-nitro-l,2,3-triazoles [487-489], During the synthesis of nitrotriazoles the bromonitroarylethenes can be replaced successfully by the more readily obtainable l,2-dibromo-l-nitro-2-arylethanes [489], The intermediate product in the synthesis of 3-nitropyrazoles from 2,2-dinitroethanol and diazo ketones or diazoacetic ester is 1,1-dinitroethene [490,491] (Scheme 68). 

Finally, triazoles ([15N2]-labelled 3,5-dibromo-lH-l,2,4-triazole and 3,5-di-chloro-lH-1,2,4-triazole) have also been studied by 15N CP MAS NMR [209]. These compounds form cyclic trimers in their crystal structures. 

Triazole reacts with bromine to afford the 4,5-dibromo derivative and an excess of hypobromite leads to l,4,5-tribromo-l,2,3-triazole. 2-Methyl-l,2,3-triazole shows in comparison a decreased readiness towards halogenation. But in the presence of iron filings as catalyst, the bromination affords 2-methyl-4,5-dibromotriazole (144) and no monobromi-nation product could be isolated (55LA(593)207). 

The H-1 atom of 4,5-dibromo-l,2,3-triazole (147) (67G109) is very acidic and forms instantly the triazolide salt (148) when treated with dimethylamine (67G109). The salt is stable even when heated to 260 °C for 140 hours and reacts smoothly in a conjugate addition reaction to give (149) (54JA4933). Methylation of (148) gives both the 1-methyl-IH and 2-methyl-2H derivatives (150) and (151) (70JHC961). 

Triazole itself forms a 4,5-dibromo derivative in high yield with bromine at 50 °C." 1-Methyl-... 

Dibromo-l-methoxymethyl-l,2,3-triazole forms the 5-lithio compound with n-butyllithium at-80 °C and 4,5-dibromo-2-methoxymethyl-l,2,3-triazole undergoes a comparable exchange. l-Phenyl-1,2,3-triazoles participate in Diels-Alder cycloadditions with dimethyl acetylenedicarboxylate using aluminium chloride catalysis, producing l-phenylpyrazoles. " ... 

Bromination occurs readily in alkaline solution giving 3,5-dibromo-l,2,4-triazole the 3-monochloro derivative can be obtained by thermal rearrangement of the A-chloro isomer an analogous N—>C 1,5-sigmatropic shift followed by tautomerisation converts the 1- into the 3-nitro compound. ... 

Dimedone was treated with two equivalents of bromine in glacial acetic acid to yield 2,2-dibromo-5,5-dimethylcyclohexane-l,3-dione. The dibromo compound was subjected to reaction with substituted 2-aminothiophenols, 2-aminophenol, thiocarbohydrazones, and triazoles to furnish spiro-(2, 6 -dioxo-4, 4 -dimethylcyclohexane)-6-substituted-l,... 

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