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Alkylation of pyrazoles

C-Alkylation of pyrazoles was a rather uneommon reaction until Grandberg and Kost found the experimental conditions necessary to obtain high yields of 4-benzylpyrazoles (66AHC(6)347). With A-unsubstituted pyrazoles a large excess of aluminum ehloride is neeessary to aeeomplish alkylation at C-4. [Pg.241]

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],... [Pg.200]

Several pyrazolo[l,2-a]pyrazoles are prepared by alkylation of pyrazoles with 1,3-dihalo compounds or with malonyl chloride (66FRP1441519 82LA420 86AP70). For example, treatments of 183 with disubstituted malonyl chlorides afford 184. Very similar to this is the formation of pyrazolo[l,2-a]-pyrazolium bromide from 1/f-pyrazoles and bromomethyloxirane (71JHC489 79JOC4473). [Pg.254]

Further examples of alkylation of imidazole derivatives were recently reported by Galous et a/.145 The nature and importance of significant factors in phase transfer alkylation of pyrazole was studied by Elguero et al.146 Their conclusions are equivalent to those of Dehmlow and Lissel.147 The optimization method used by Elguero et al. (several parameters at a time) is different from the conventional procedure (one parameter at a time) and will probably find applications in the future for optimization of organic syntheses. [Pg.201]

Tarrago et al.149 have reported an interesting example of a change in selectivity induced by PT catalysis. In N-alkylation of pyrazoles (83), the ratio 84/85 is different under neutral or alkaline conditions, especially when a heteroatom with a lone pair is located ortho to one of the nitrogens of the... [Pg.201]

Benzylindazole and l-benzyl-4-bromo-3,5-dimethylpyrazole were efficiently debenzylated with potassium tert-butoxide in DMSO and oxygen at room temperature <2002TL399>. Alkylation of pyrazoles 443 with 2,2-dichloro-ethyl ether under conditions of phase-transfer catalysis gave A -[2-(2-chloroethoxy)ethyl]pyrazoles 444, which underwent dehydrochlorination with potassium hydroxide in DMSO giving A -(2-vinyloxyethyl)pyrazoles 445 (Scheme 51) <2004RJC1264>. [Pg.67]

Alkylation of pyrazol-3-ones usually occurs not only on side-chain substituents such as primary amino groups but also on the nitrogen atom of the unsubstituted lactam group. Alkylation can also occur on a stabilized carbanion generated from a methyl group by a strong base. [Pg.29]

Holzer and Plagens (97H309) (Scheme 24) studied the alkylation of pyrazol-3-ones 62 and of the tautomeric pyrazol-3-one 78a-d/pyrazol-5-ol 79a d mixtures by applying the Mitsunobu reaction [triphenylphosphine, diethyl azodicarboxylate (DEAD), alcohol, solvent]. The reactions were performed in various solvents. Using methanol as the alkylating agent the reaction of 62 in dichloromethane or THF,... [Pg.152]

Alkylation of pyrazol-3-one 70 with 4-[morpholin-4-yl-(4-nitrophenyl)methyl]-morpholine 84 was performed at room temperature since at higher temperatures polymerization occurred. However the reaction was extremely slow. It took... [Pg.153]

Diesters, diacid dichlorides and dihaloalkanes react with pyrazolidine or its derivatives to give varying yields of products containing the pyrazolo[l,2-a]pyridazine moiety. For example, pyrazolidine reacts with diethyl succinate <62HCA37, 72JHC4i>. Alkylation of pyrazoles with cw-1,4-dichloro-2-butene under PTC conditions also gives products of intramolecular cyclization <89KGS497>. [Pg.815]

The third reaction studied was the alkylation of pyrazoles with alkyl halides. This reaction was not possible using the ionic liquid heating technique, because the aryl halide reacted with the ionic liquid at the elevated temperatures used in the reaction. This highlights one of the limitations of this method. [Pg.356]

Scheme 6.12 A two-step convenient alkylation of pyrazoles in a one-pot operation... [Pg.197]

Alkylation of pyrazoles in basic solution involves an A-anion, and proceeds straightforwardly. ... [Pg.398]

Alkylation Reactions of Pyrazole Matos et al. proposed for the first time (Cs)Al-SBA-15 and DEAPTS/ MCM-41 mesoporous materials (where DEAPTS is diethylamino propyl) as efficient basic catalysts in the alkylation of pyrazole and diethyl iminodiacetate with various reactive alkyl bromides under conventional thermal activation (Scheme 21) [92]. The alkylation of pyrazole catalyzed by both (Cs)Al-SBA-15 and DEAPTS/MCM-41 catalysts in the presence of a solvent (acetonitrile or dimethylformamide (DMF)) afforded selectively N-alkylpyrazole 30 with high... [Pg.389]

SCHEME 21 Alkylation of pyrazole ring with different reactive aUcyl bromides. [Pg.390]

The synthesis of N-alkylpyrazoles was also carried out over different pillared saponites impregnated with cesium [93]. The alkylation of pyrazole with different alkyl bromides was conducted using acetonitrile or DMF as solvents, at 338-353 K, achieving total conversion and selectivity after Ih of reaction time. The reactivity order found for the different alkyl bromides seemed to depend on the solvent used in the reaction and the different coordination properties of Cs+ on the catalysts. [Pg.390]

Although A-alkylation is one of the most important and most studied reactions of pyrazoles, its quantitative (orientation ratios) and qualitative (mechanism) aspects are still unclear. All the classical results are reported in (67HC(22)l, B-76MI40402) and can be summarized as follows. [Pg.229]

The behaviour of pyrazoles towards nitrosation is similar to their behaviour described above towards diazo coupling, i.e. aminopyrazoles and pyrazolones readily react with nitrosation agents, like alkyl nitrites (81FES1019), to afford stable nitroso derivatives. Some simple nitrosopyrazoles have been isolated, for example the blue-green 3,5-dimethyl-4-nitrosopyrazole, and many others have been proposed as reactive intermediates in the direct conversion of pyrazoles into diazonium or diazo derivatives (Scheme 25) (B-76MI40402). [Pg.242]

Application of the Knorr pyrazole synthesis has also been demonstrated on solid support. ° To prepare trisubstituted pyrazoles, the diketone was linked to the solid support to make 57 using a linker with an amide bond. Alkylation of the diketone followed by condensation of the hydrazine with the resulting diketone gave the desired pyrazoles as mixtures of isomers. Subsequent cleavage of the amide bond linker then provided the pyrazole amides 59. ... [Pg.298]

Fig. 14 Microwave-assisted synthesis of pyrazoles and isoxazoles on cellulose. Reagents and conditions a Camphorsulfonic acid, DMF, MW 80 °C, 15 min, open vessel b NH2XH, MW 82 °C, 15 min, open vessel. X = N,0 Y = NH, NEt, O R = Me, i-Pr, BUCH2, PhCH2, Et(Ph)CH, R = alkyl, aUyl, and aryl groups... Fig. 14 Microwave-assisted synthesis of pyrazoles and isoxazoles on cellulose. Reagents and conditions a Camphorsulfonic acid, DMF, MW 80 °C, 15 min, open vessel b NH2XH, MW 82 °C, 15 min, open vessel. X = N,0 Y = NH, NEt, O R = Me, i-Pr, BUCH2, PhCH2, Et(Ph)CH, R = alkyl, aUyl, and aryl groups...
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. ... [Pg.8]

Protected 6-amino-hexahydro-l,7-dioxopyrazolo[l,2-4]pyrazole-2-carboxylic acid 274 is available by a thermolytic decomposition of diazo compound 273 via the Wolff rearrangement. The starting compound is simply available by alkylation of racemic 272 with the corresponding bromoacetoacetate and subsequent diazo transfer reaction (Scheme 35) <1996TL4891>. [Pg.407]

Fused pyrazole compounds have been prepared from A-alkyl substituted pyrazoles. For example, a palladium-catalyzed/norbornene-mediated sequential coupling reaction involving an aromatic sp2 C-H functionalization as the key step has been described, in which an alkyl-aryl bond and an aryl-heteroaryl bond were formed in one pot <060L2043>. A variety of highly substituted six-membered annulated pyrazoles 59 were synthesized in a one-step process in moderate yields from IV-bromoalkyl pyrazoles 57 and aryl iodides 58. [Pg.216]

Alkylation of 2-(pyrazol-l -yl)pyridine 706 with 1,2-dibromoethane afforded (81JHC9) pyrazolo[r,2 -a]pyrido[2,l-c][l,2,4]triazinedium dibromide 707. [Pg.300]


See other pages where Alkylation of pyrazoles is mentioned: [Pg.215]    [Pg.202]    [Pg.354]    [Pg.29]    [Pg.215]    [Pg.239]    [Pg.215]    [Pg.202]    [Pg.354]    [Pg.29]    [Pg.215]    [Pg.239]    [Pg.309]    [Pg.53]    [Pg.183]    [Pg.218]    [Pg.228]    [Pg.265]    [Pg.269]    [Pg.772]    [Pg.168]    [Pg.124]    [Pg.204]    [Pg.148]    [Pg.151]    [Pg.86]    [Pg.86]    [Pg.209]    [Pg.211]   
See also in sourсe #XX -- [ Pg.6 ]




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Alkylation of pyrazole

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