Alkylation of triazole

Additionally, substituents on the triazole ring will direct the orientation of alkylation. The 4-phenyl-IH-1,2,3-triazole tends to give the 1-methyl and 2-methyl isomers in 62% and 38% when treated with dimethyl sulfate. The l-methyl-5-phenyl derivative was not found due to steric effects.  

The alkylation of 1,2,4-triazole prefers to give the N-1 substitued product rather than the N-4 substituted product. However, the alkylation product of either N-1 or N-2 is difficult to predict when triazole has 3- or 5-substituents. Generally, the ratio of both products depends on the properties of the alkylating agent.  

An example of alkylation of a 3-substituted triazole is shown below  

A -Difluoromethylation of 3-phenyl-1,2,4-triazole yields three products by using chlorodifluoromethane and base with N-1 substituted compound as the major product. Additionally, iV-trimethylsilylazole can be alkylated at N-1 with -butylbromide in a 90% yield.  

Anastrozole is an aromatase inhibitor that is used to treat breast cancer by decreasing the amount of estrogen synthesized by the human body. The synthesis of anastrozole entails a selective bromination and alkylation reaction with 1,2,4-triazole. 

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Molidustat can be synthesized [137, 138] as described in Scheme 2.8. The compound 148 in the scheme is prepared by alkylation of triazole. Alternatively, they can also be prepared by a (3-1-2) cycloaddition of compounds 146 and 147 to a cycloadduct, followed by a retro-Diels-Alder reaction of the adduct to provide the desired compound 148 along with compound 149 (Scheme 2.15). 

For both azole and benzazole rings the introduction of further heteroatoms into the ring affects the ease of quaternization. In series with the same number and orientation of heteroatoms, rate constants increase in the order X = 0requires stronger reagents and conditions methyl fluorosulfonate is sometimes used (78AHC(22)71). The 1-or 2-substituted 1,2,3-triazoles are difficult to alkylate, but methyl fluorosulfonate succeeds (7IACS2087). 

Simple 1,2,4-triazole derivatives played a key role in both the synthesis of functionalized triazoles and in asymmetric synthesis. l-(a-Aminomethyl)-1,2,4-triazoles 4 could be converted into 5 by treatment with enol ethers <96SC357>. The novel C2-symmetric triazole-containing chiral auxiliary (S,S)-4-amino-3,5-bis(l-hydroxyethyl)-l,2,4-triazole, SAT, (6) was prepared firmn (S)-lactic acid and hydrazine hydrate <96TA1621>. This chiral auxiliary was employed to mediate the diastereoselective 1,2-addition of Grignard reagents to the C=N bond of hydrazones. The diastereoselective-alkylation of enolates derived from ethyl ester 7 was mediated by a related auxiliary <96TA1631>. 

Propiolaldehyde diethyl acetal has found numerous synthetic applications in the literature which may be briefly summarized. The compound has been utilized in the synthesis of unsaturated and polyunsaturated acetals and aldehydes by alkylation of metal-lated derivatives, " by Cadiot-Chodkiewicz coupling with halo acetylenes, " and by reaction with organocuprates. Syntheses of heterocyclic compounds including pyrazoles, isoxazoles, triazoles, and pyrimidines have employed this three-carbon building block. Propiolaldehyde diethyl acetal has also been put to use in the synthesis of such natural products as polyacetylenes " and steroids. ... 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

Loupy et al. [70] have studied the effect of solvent on the selectivity of the alkylation of 1,2,4-triazole 62 by 2,2, 4 -trichloroacetophenone 63 (Scheme 4.31) under MW and conventional heating. The reactions were all performed at 140 °C. 

Alkylation of 1,2,3-triazole with Ar-(2-bromocthyl)phthalimidc in the presence of Cs2C03 followed by cleavage of the phthalyl moiety with hydrazine provides l-(2-aminoethyl)-l,2,3-triazole 94 in 51% yield <2003JME1116>. A reaction of 4-nitro-l,2,3-triazole with propargyl bromide in the presence of KOH gives a mixture of isomeric 1-propargyl-l,2,3-triazoles 95 and 96 in the equimolar ratio <2003RJ01792>. However, in acidic media, when N-l... 

Alkylation of the 1,2,4-triazole ring by alkyl radical species has been achieved reaction of 1-methyl-1,2,-4-triazole 37 with alkyl carboxylic acids in the presence of a silver catalyst gave the corresponding 2-alkylated triazoles 38a-e in moderate yields (Equation 9 and Table 1) <2001TL7353>. 

Table 1 Alkylation of 1 -methyl-1,2,4-triazole 37 using radical species (Equation 9)...

Alkylation of 1,2,4-triazole has been investigated in some depth as was expected, reaction of 1,2,4-triazole with a wide variety of electrophilic reagents in the presence of an equally diverse array of basic reagents gave both 1-alkyl-1,2,4-triazole and 4-alkyl-l,2,4-triazole products but always in the approximate ratio of 90 10 in favor of the 1-alkylated product <2000TL1297>. 

Table 4 Alkylation of solid-supported 1,2,4-triazole derivatives (Equation 15) ...

The alkylation of 4-amino-l,2,4-triazolo-3-thione derivatives using haloalkyl nitriles to give the S-alkylated product as a result of alkylation of the 3-mercato-l,2,4-triazole tautomer, or the corresponding N-alkylated product resulting from reaction with the 3-thione tautomer, has been studied extensively optimum conditions have been developed to provide either the S- or the N-alkylated products in good yields <2000PS(167)219, 2003BML2601>. 

Triazoline-3,5-dione 184 underwent an ene reaction with olefins 183 to yield trialkylated allylic urazoles 185, which were further elaborated into allylic amines 186 . DBU has been found to be a mild and convenient base for the alkylation of 1,2,4-triazole with various alkyl halides in the high yielding syntheses of 1-substituted-1,2,4-triazoles <00TL1297>. 

The AT-alkylation of 2,7-diethyl-pyrazolo[l,5-A [l,2,4]triazole 179 has been extensively investigated <1998CPB69, 1998CPB287>. As shown, reaction of, /V-triphenylmethyl-5-[5-[4 -(bromomethyl)biphenyl-2-yl]tetrazole with... 

Reactions of Phosphonic and Phosphinic Acid Derivatives.—The reactions of phos-phonic and thiophosphonic amides and chlorides with carboxylic acid chlorides and amides have been discussed.101 Dialkyl alkylphosphonates and alkyl dialkylphos-phinates may be used for the iV-alkylation of imidazoles, triazoles, and pyrroles.105... 

Despite the greater acidities of the diazoles and triazoles (pKa = 10-14), fairly vigorous reaction conditions are still required for the alkylation of the unsubstituted systems [26] (Table 5.32) and the effectiveness of the alkylation of pyrazoles and imidazoles is enhanced under solidiliquid conditions [27-30]. Under these conditions, quaternization is avoided if no solvent is added [27],... 

Predictably, 1,2,4-triazole is alkylated preferentially at the 1-position [36, 38,39]. Specific alkylation at the 4-position can be achieved by the initial reaction with dibromomethane to form the bis-triazol-l-ylmethane (see below), followed by quat-emization of the triazole system at the 4-position and subsequent C-N cleavage of the 1,1 -methylenebistriazolium salts [40]. 1,2,3-Benztriazole yields a mixture of the isomeric 1- and 2-alkylated derivatives [41]. The 1-isomer predominates, but the ratio depends on whether the reactions are conducted in the presence, or absence, of a nonpolar organic solvent (Table 5.33). Higher ratios of the 1-isomer are obtained under solidrliquid two-phase conditions. Thus, alkylation of 1,2,3-benztriazole with benzyl chloride produces an overall yield of 95% with the l- 2-isomer ratio of ca. 5.7 1 similar reactions with diphenylmethyl and triphenylmethyl chlorides gives overall yields of 95% (9 1 ratio) and 70% (100% 1-isomer), respectively [38], 6-Substituted purines are alkylated at the N9-atom and reaction with 1-bromo-3-chloropropane yields exclusively the 9-chloropropyl derivative (cf. reaction wi phenols) [42]. 

Relatively few additions of the lower molecular weight alkyl azides have been performed, mainly because of their volatility and thermal sensitivity simple alkyltriazoles are normally obtained by alkylation of the w-triazoles. On the other hand, a very wide range of less volatile substituted alkyl azides has been added to acetylenes Their addition to acetylenic esters usually proceeds readily and provides a useful method of characterizing the azides. Benzyl azide has often been used because it is relatively stable (up to 150°), it is readily prepared, and the benzyl group can be removed from the resulting triazoles (Section IV, E). 

Alkylation of thiazolo[3,2-fi][l,2,4]triazoles takes place at N(l). Treatment of 180 with 2-bromo-l-arylethanones (acetone, heating) yields 181 [94JAP(K)06/184165, 94TL4587]. 

Aminothiazole[3,2-fe][l,2,4]triazoles are readily bis-N-acylated (Ae20, reflux). The 5-alkylation of thiazolo[3,2-b][l,2,4]triazoles with chloro- and aeetoxymethylcephem was also reported (91MI2). An 5-alkylated thia-zolo[3,2-fe][l,2,4]triazole was converted to a sulfonyl ehloride and aminated (88EUP244098). 

Alkylation of 1,2,4-triazolidines with 1,3-dibromopropane gives l-(3-bromopropyl) derivatives which are cyclized to pyrazolo[l,2-a]-l,2,4-triazoles [79JAP(K)1645]. The syntheses ofpyrazolo[l,2-a]-l,2,4-triazoles from pyrazole starting materials include the reactions of isocyanates (253)... 

As an alternative, initial S-alkylation of aminoazole 8 with appropriate alkyl-bromides (R3CH2Br) was performed. Then 3-amino-5-alkylthio-l,2,4-triazoles 11 were introduced into the MCRs with aromatic aldehydes and acetoacetamides (pathway b ). To sufficiently increase yields of target heterocycles 13, the cyclocondensations were performed under microwave irradiation in ethanol at 120°C. 

The alkylation of 5-(4-hydroxyphenoxy)-l/f-l,2,3-triazoles (147) under alkaline conditions exclusively yields the isomeric N(2) and N(3) alkylation products (148) and (149) (Equation (9)). For R = PhCH2, the N(2) and N(3) isomers are obtained in almost equal amounts, but for R = PhjC, only 1% of the N(3) isomer is formed because of steric hindrance. No N(l) alkylation is observed. Acylation and sulfonation of (147) under similar conditions results in attack at the phenolic oxygen <82JHCl 147>. Reaction of benzotriazole with 2-chlorothiophen-3-ones (150) in acetic acid gives 5-(benzotriazol-l-yl)-3-hydroxythiophene-2-carboxylates (151) (Equation (10)) <87JHC1301>. 

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