A fast and efficient bromination of isoxazoles and pyrazoles by microwave irradiation

Guo, Li; Kakarla, Ramesh; Gerritz, Samuel W.

doi:10.1016/j.tetlet.2007.04.118

Cited by 44 publications

(16 citation statements)

References 14 publications

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“…NBS is also found suitable for ring bromination of isoxazole, 881−883 pyrazole and its derivatives, 882,883 and furan. 884 Under microwave irradiation, isoxazole and pyrazoles are converted to the monobrominated products in good yields.…”

Section: Aromatic Bromination Using Nbsmentioning

confidence: 99%

“…884 Under microwave irradiation, isoxazole and pyrazoles are converted to the monobrominated products in good yields. 882 In this method, NBS was used in different acid solvents according to the reactivity of the substrates. Trifluoro-acetic acid was found to be the best solvent for highly unreactive isoxazoles and pyrazoles (Scheme 271).…”

Section: Aromatic Bromination Using Nbsmentioning

confidence: 99%

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Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

2016

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Bromination is one of the most important transformations in organic synthesis and can be carried out using bromine and many other bromo compounds. Use of molecular bromine in organic synthesis is well-known. However, due to the hazardous nature of bromine, enormous growth has been witnessed in the past several decades for the development of solid bromine carriers. This review outlines the use of bromine and different bromo-organic compounds in organic synthesis. The applications of bromine, a total of 107 bromo-organic compounds, 11 other brominating agents, and a few natural bromine sources were incorporated. The scope of these reagents for various organic transformations such as bromination, cohalogenation, oxidation, cyclization, ring-opening reactions, substitution, rearrangement, hydrolysis, catalysis, etc. has been described briefly to highlight important aspects of the bromo-organic compounds in organic synthesis.

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Section: Aromatic Bromination Using Nbsmentioning

confidence: 99%

Section: Aromatic Bromination Using Nbsmentioning

confidence: 99%

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

2016

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“…Recently, Li et al reported the bromination of isoxazoles with N-bromosuccinimide in acid solvents using microwave irradiation [14]. The work included the synthesis of methyl 4-bromo-5-phenylisoxazole-3-carboxylate (3a).…”

Section: Resultsmentioning

confidence: 99%

4-Halo-1,3-oxazoles: Unambiguous structural assignment of 2-halo-2-benzoyl-2H-azirine-3-carboxylates thermal ring expansion products

Lopes

Nunes

Fausto

et al. 2009

Journal of Molecular Structure

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a b s t r a c t IR spectroscopy in cryogenic argon matrix of methyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate and methyl 4-chloro-5-phenylisoxazole-3-carboxylate was applied for the structural assignment of these isomeric heterocycles. It was demonstrated that methyl 2-benzoyl-2-halo-2H-azirine-3-carboxylates undergo thermal ring expansion to give 4-halo-5-phenyl-1,3-oxazole-2-carboxylates and not the isomeric isoxazoles.

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“…The green and red circles point to the most reactive site according to the predictions, while the arrow indicates the site of the actual reaction. For the 1 H spectrum, the variation of 0.1 ppm is accepted, and for 13 C spectrum, the variation of 5 ppm relative to the lowest predicted value is accepted. − …”

Section: Resultsmentioning

confidence: 99%

Computational Methods to Predict the Regioselectivity of Electrophilic Aromatic Substitution Reactions of Heteroaromatic Systems

et al. 2016

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The validity of calculated NMR shifts to predict the outcome of electrophilic aromatic substitution reactions on different heterocyclic compounds has been examined. Based on an analysis of >130 literature examples, it was found that the lowest predicted (13)C and/or (1)H chemical shift of a heterocycle correlates qualitatively with the regiochemical outcome of halogenation reactions in >80% of the investigated cases. In the remaining cases, the site of electrophilic aromatic substitution can be explained by the calculated HOMO orbitals obtained using density functional theory. Using a combination of these two methods, the accuracy increases to >95%.

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A fast and efficient bromination of isoxazoles and pyrazoles by microwave irradiation

Cited by 44 publications

References 14 publications

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

Use of Bromine and Bromo-Organic Compounds in Organic Synthesis

4-Halo-1,3-oxazoles: Unambiguous structural assignment of 2-halo-2-benzoyl-2H-azirine-3-carboxylates thermal ring expansion products

Computational Methods to Predict the Regioselectivity of Electrophilic Aromatic Substitution Reactions of Heteroaromatic Systems

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