Pyrazoles. 6. Synthesis of novel heteroaryl 4‐pyrazolyl ketones

Hahn, M.L.; Heinisch, G.; Hölzer, W.; Schwärz, H.

doi:10.1002/jhet.5570280505

Cited by 18 publications

(6 citation statements)

References 12 publications

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“…One route was inspired from previous work on heteroaryl 4-pyrazolyl ketones. 47 It consisted of using direct lithiation of the 4-bromo pyrazole (commercially available or synthesized in one step by monobromination of pyrazole) with 3 equivalents of n-BuLi, which gave the intermediate 1,4-dilithiopyrazole, which could in turn be converted into the formylated compound by adding dry dimethylformamide to the reaction mixture. In the course of optimizing the reaction, we found that some parameters were particularly crucial to enhance the yield.…”

Section: Synthesis Of the Organic Radicalmentioning

confidence: 99%

Polymorphs of a pyrazole nitronyl nitroxide and its complexes with metal(ii) hexafluoroacetylacetonates

et al. 2006

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The synthesis of pyrazol-4-yl nitronyl nitroxide is reported, along with the crystal structures of its polymorphs and coordination compounds with nickel(II) and cobalt(II) hexafluoroacetylacetonate. The polymorphic forms of the pure radical show very different magnetic properties: the alpha form shows only antiferromagnetic interactions while those of the beta form reveal competing ferro-and anti-ferromagnetic interactions. This phenomenon can be traced to the relative orientations of the spin carriers in the crystal. These, in turn, are determined in large measure by the hydrogen bonding networks, where a competition between [N-H … O] and [N-H … N] hydrogen bonds is observed. This delicate balance is also seen in the coordination chemistry of the radical acting as a ligand for the hexafluoroacetylacetonate complexes of nickel(II) and cobalt(II). In the former, a 2 : 1 radical : metal complex is formed because of coordination of the pyrazolyl nitrogen atom only. In the latter, a cyclic dimer is formed which involves both the nitrogen and oxygen as coordinating atoms. In both cases, the NH groups of the pyrazolyl moiety lead to the formation of hydrogen bonded networks in the crystals. The magnetic properties of the complexes reveal antiferromagnetic interactions. However, the pyrazolyl nitronyl nitroxide has been proven an interesting component for the formation of coordination compounds with hydrogen bonds in between the magnetic components.

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Section: Synthesis Of the Organic Radicalmentioning

confidence: 99%

Polymorphs of a pyrazole nitronyl nitroxide and its complexes with metal(ii) hexafluoroacetylacetonates

et al. 2006

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“…However, there are only few examples of pyrazole C-4 lithiation. [42][43][44][45] Such reactions proceed with low selectivity, due to competing deprotonation at C-5 [42] or isomerization of the 4-lithiopyrazole to the corresponding 5-lithiopyrazole. [46] This problem can be circumvented through the introduction of a second protecting group at C-5, [47] but the overall multi-step synthesis makes such an option not very attractive, in our opinion.…”

Section: Introductionmentioning

confidence: 99%

One‐Step Synthesis of Symmetrically Substituted 2,6‐Bis(pyrazol‐1‐yl)pyridine Systems

Zoppellaro

Baumgarten

2005

Eur J Org Chem

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A one‐pot synthetic route that allows functionalization of the 2,6‐bis(pyrazol‐1‐yl)pyridine backbone in the 4‐ and 4″‐pyrazole positions by direct H(4)‐pyrazole halogen exchange is described. The diiodo derivative in particular provides easy access to additional functionalities through both Sonogashira and Grignard exchange reactions. These synthons represent optimal building blocks for the extension of the chelating core and for the assembly of rigid organic and metalloorganic nanostructures. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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“…An alternative approach to 4-substituted pyrazoles would be reaction of 4-lithiopyrazoles with electrophiles. However, there are only a few examples of pyrazole C-4 lithiation, − all based on bromine−lithium exchange. This reaction sometimes proceeds with low chemoselectivity due to competing deprotonation at C-5 , or isomerization of initially formed 4-lithiopyrazole to 5-lithiopyrazole .…”

Section: Introductionmentioning

confidence: 99%

Regioselective Introduction of Electrophiles in the 4-Position of 1-Hydroxypyrazole via Bromine−Lithium Exchange

1999

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Two protocols for introduction of electrophiles at the 4-position of 1-hydroxypyrazoles have been developed. The first is deprotonation of 4-bromo-1-[(tert-butyldiphenylsilyl)oxy]pyrazole (6) with LDA to produce the 5-lithio derivative in which the silyl group migrates spontaneously from oxygen to C-5 affording 4-bromo-5-(tert-butyldiphenylsilyl)-1-lithoxypyrazole (8). Subsequent treatment with t-BuLi causes bromine-lithium exchange to give 5-tert-butyldiphenylsilyl-4-lithio-1-lithoxypyrazole which is trapped with electrophiles affording 4-substituted 5-(tert-butyldiphenylsilyl)-1-hydroxypyrazoles 9a-e in a one-pot sequence. The second is treatment of 4-bromo-1-hydroxypyrazole (5) with excess LDA and trimethylsilyl chloride to produce 3,5-bis(trimethylsilyl)-4-bromo-1-hydroxypyrazole (12), which upon sequential metalation with n-BuLi and reaction with electrophiles affords 4-substituted 3,5-bis(trimethylsilyl)-1-hydroxypyrazoles 13a-e. The tert-butyldiphenylsilyl group of 9a and the trimethylsilyl groups of 12 can be removed selectively by treatment with tetrabutylammonium fluoride in THF in the presence of trifluoroacetic acid.

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Pyrazoles. 6. Synthesis of novel heteroaryl 4‐pyrazolyl ketones

Abstract: The preparation of a variety of novel heteroaromatic analogues of benzophenone 2–11 characterized by a 4‐pyrazolyl moiety and a thienyl‐, azinyl‐ or diazinyl‐system starting from 1,4‐dilithiopyrazole is reported.

Cited by 18 publications

References 12 publications

Polymorphs of a pyrazole nitronyl nitroxide and its complexes with metal(ii) hexafluoroacetylacetonates

Polymorphs of a pyrazole nitronyl nitroxide and its complexes with metal(ii) hexafluoroacetylacetonates

One‐Step Synthesis of Symmetrically Substituted 2,6‐Bis(pyrazol‐1‐yl)pyridine Systems

Regioselective Introduction of Electrophiles in the 4-Position of 1-Hydroxypyrazole via Bromine−Lithium Exchange

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