1.2.3- Triazole 2-methoxy

The extranuclear C-nitrosoquinoxalines are typified by 3-(a-methoxycarbonyl-a-nitrosomethyl)-2(l/i)-quinoxalmone (66), made by nitrosation of 3-(methoxy-carbonylmethyl)-2(l/f)-quinoxalmone (65) [AcOH, CI3CO2H, C5H11ONO, 20°C, 3 h 91% spectra suggest that the hydroxyimino tautomer (67) may predominate] and was subsequently reduced to afford 3-(a-amino-a-methoxycarbonylmethyl)-2(l//)-quinoxafinone (68) (PtOa, H2, 1 atm, THF, EtOH, 20°C, 4 h 59%) also by 3-[a-(4-amino-5-methyl-4//-l,2,4-triazol-3-yl)-a-nitrosomethyl]-2(l//)-quinoxa-linone (69, R = NO), prepared by nitrosation of 3-(4-amino-5-methyl-4//-1,2,4-triazol-3-ylmethyl)-2(177)-quinoxalinone (69, R = H) [NaN02 ( 1.25 equiv), AcOH, H2O, no further details 79%]." ... 

CN 4-[4-[4-[4-[[2-(2,4-dichlorophenyl)-2-( 1H-1,2,4-triazol-1 -ylmethyl)-1,3-dioxolan-4-yl]methoxy]phenyl]-l-piperazinyl]phenyl]-2,4-dihydro-2-(l-methylpropyl)-3//-l,2,4-triazol-3-one... 

Dihydro-3-methoxy-4-methyl-5-oxo-A/-[[2-(tri-fluoromethoxy)phenyl]sulfonyl]-1H-1,2,4-triazole-1-carboxamide, sodium salt... 

Tetranitro derivative 90 (z-TACOT Section 12.10.15.5) treated with methanolic sodium methoxide at ambient temperature does not lead to simple product of nucleophilic substitution of a nitro group but provides compound 92. Its formation can be rationalized by introduction of the methoxy group into the 1-position, followed by scission of the remote triazole ring of 91 to give the final product. Compound 90 subjected to the vicarious nucleophilic substitution (VNS) conditions using either hydroxylamine or trimethylhydrazinium iodide gives a very insoluble red solid, which was identified as l,3,7,9-tetraamino-2,4,8,10-tetranitrobenzotriazolo[2,l- ]benzotriazole 93 (Scheme 5) <1998JOC3352>. 

Ethyl diazoacetate, 1503 Ethyl 4-diazo-l,2,3-triazole-5-carboxylate, 1853 Lithium diazomethanide, 0379 3-Methoxy-2-nitrobenzoyldiazomethane, 3124 Methyl diazoacetate, 1138... 

Methoxy-l,2,3,4-thiatriazole, 0773 1-Methyl-1,2,3-triazole, 1189 4-Nitroamino-1,2,4-triazole, 0777 4-Nitro-l-picryl-l,2,3-triazole, 2886 3-Nitro-l,2,4-triazolone, 0716 1-Picryl-l,2,3-triazole, 2893... 

Imidazolidinium salts can also be transformed into the corresponding diamino ortho-esters by alkaline alkoxylate, and upon alcohol elimination at elevated temperature the imidazolidin-2-ylidenes can be trapped. The reaction of tria-zolium salts with sodium methanolate in methanol yields 5-methoxy-4,5-dihydro-IH-triazole which also eliminates methanol upon heating in vacuo. The resulting triazolin-5-ylidenes can either be isolated or trapped by an appropriate metal precursor [Eq. (19)]. Benzimidazolin-2-ylidenes are similarly accessible by this route. 

As mentioned earlier, triazolium salts can be converted into 5-methoxy-4,5-dihydro-lH-triazoles by reacting them with sodium methanolate in methanol. The heterocycles eliminate methanol upon heating in vacuo [Eq. (21)] and the formed triazolin-5-ylidenes can then be isolated. " The same method works with imidazolium and benzimidazolium salts." ... 

Not surprisingly, it is rather difficult to separate the different contributions of the different interactions as they occur in the micellar Stern region. In an attempt to solve this problem, the group of Engberts used a series of hydrolysis reactions of activated esters and amides to probe the reaction environment offered by micelles. The reactions initially involved the water-catalyzed pH-independent hydrolysis reactions of i-methoxy-phenyl dichloroacetate 4 and l-benzoyl-3-phenyl-l,2,4-triazole 5, as extensive information on the rate retarding effects of added cosolutes on this reaction was available. ... 

Different synthetic routes have been used to prepare these carbenes (Scheme 8.6). The most common procedure is the deprotonation of the conjugate acid. In early experiments, sodium or potassium hydride, in the presence of catalytic amounts of either f-BuOK or the DMSO anion were used. ° Then, Herrmann et al. showed that the deprotonation occurs much more quickly in liquid ammonia as solvent (homogeneous phase), and many carbenes of type IV have been prepared following this procedure. In 1993, Kuhn and Kratz" developed a new and versatile approach to the alkyl-substituted N-heterocyclic carbenes IV. This original synthetic strategy relied on the reduction of imidazol-2(3//)-thiones with potassium in boiling tetrahydrofuran (THF). Lastly, Enders et al." reported in 1995 that the 1,2,4-triazol-5-ylidene (Vila) could be obtained in quantitative yield from the corresponding 5-methoxy-l,3,4-triphenyl-4,5-dihydro-l//-l,2,4-triazole by thermal elimination (80 °C) of methanol in vacuo (0.1 mbar). 

The reaction of unsymmetrically substituted 1,3-diketones such as 5-acetoacetyl-6-methoxy-2,3-diphenylbenzofuran or its 6-acetoacetyl-5-methoxy isomer with 5-amino-2-phenyl-l,2,4-triazol-3-one (72) could produce 74 and/or 76. However, a single product was obtained which was assigned the structure 74 on the basis of spectral properties (88PJS334) (Scheme 32). 

Derivatives have also been obtained in which the 1,2,3-triazole ring is substituted by chlorine83 and/or methoxy groups,66 as, for example, in the formation of the stilbene 148 from 2-(jP-tolyl)-5,7-dimethyl-benzoxazole (146) and Schiff s base 147. 

H5, which was found to be 1.8 1 in 456 (R = Me), 2.4 1 in 456 (R=CH2Ph), and 6.1 1 in 456 (R=Ph) (1987ACSA(B)724). Substituents such as a halogen or a methoxy group enhance the acidity of adjacent protons significantly. Expectedly, the electron-attracting substituents stabilize the adjacent anion inductively. The generation and application of 1,2,3-triazole anions in synthesis are discussed in Section 4.1.6.2-5 (Scheme 141). 

Substituted 1,2,3-triazole 1-oxides 448 are protonated at the oxygen atom. The site of the protonation is evident from1H and 13C NMR spectra, which are similar to those of the l-methoxy-l,2,3-triazolium tetrafluorob-orates 507 described in Section 4.2.7.10. The hydrochlorides are manipula-ble and separate from solutions in dry methanol upon addition of diethyl ether (1987ACSA(B)724). 

The 3-substituted 1,2,3-triazole 1-oxides 448 were alkylated at the oxygen by trimethyloxonium tetrafluoroborate using liquid sulfur dioxide as the solvent affording hygroscopic 3-substituted l-methoxy-l,2,3-triazolium tetrafluoroborate 507 in high yield (1987ACSA(B)724).The reactivity of these salts has not been reported (Scheme 147). 

The hydroxytriazole 1-oxides 500 and 502 when treated with methyl iodide were methylated predominantly at the N-oxygen affording mesoionic anhydro l-methoxy-3-methyl-4-hydroxy- or 5-hydroxy-l,2,3-triazolium hydroxide 501 or 503 (Scheme 146) (1987ACSA(B)724). In both cases methylation at the C-hydroxy group took place to a minor extent giving rise to methoxy-substituted triazole 1-oxides 499 or 503, respectively. Under similar conditions 3-methyl 4-hydroxy-5-chloro-l,2,3-triazole 1-oxide 505 produced a 2 1 mixture of the C-methoxy and the N-methoxy derivatives 504 and 506. The mesoionic triazoles 501, 503, and 506 were dealkylated upon heating with 1-M sodium methoxide, reforming the hydroxy-substituted N-oxides 500, 502, and 505, respectively. 

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