Rates of thermolysis of azidobenzenes in solution: large stabilizations of transition states by charge transfer from electron-donor substituents

Dyall, LK; L'abbé, G.; Dehaen, Wim

doi:10.1039/a606704b

Cited by 9 publications

(2 citation statements)

References 17 publications

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“…There has been speculation as to whether the ring opening of azidoheterocycles occurs at the stage of the nitrene, or whether it is concerted with loss of nitrogen from the azide. , Our observation of ring-retained products establishes that the azide 12 does form nitrene on irradiation, although it does not unambiguously establish that this intermediate is also the precursor of the ring-cleavage products. The alternative however is to say that the outcome is determined during irradiation.…”

Section: Discussionmentioning

confidence: 71%

Photochemistry of 2-Azido-1-methylimidazole in Aqueous Solutions. Observation of the 1-Methyl-2-imidazolylnitrenium Ion

and

McClelland

1999

J. Am. Chem. Soc.

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Irradiation of 2-azido-1-methylimidazole (12) in aqueous solution gives products from two reaction channels. One pathway involves a ring opening typical of azidoheterocycles. The observed products are glyoxal bis-hydrate, the methylammonium ion, and cyanamide; a glyoxal bis-oxime is presumed to be the intermediate initially formed in the ring opening. The other pathway leads to products that retain the five-membered ring, the 2-amino-4,5-dihydro-4,5-dihydroxy-1-methylimidazolium ion 3, its monophosphate ester 6 when the irradiation is carried out in phosphate buffer, and glutathione adducts 7 and 8 when glutathione (GSH) is present. These products have been previously observed in the reactions of 2-hydroxylamino-1-methylimidazole in aqueous solution, and arise from reaction of the 1-methyl-2-imidazolylnitrenium ion (2 + ) with water, phosphate, and GSH. This pathway is therefore proposed to involve formation of the cation 2 + via protonation of the singlet 1-methyl-2-imidazolylnitrene 13 formed upon irradiation of the azide. A single transient species undergoing exponential decay with λmax at 230−235 nm is observed with flash photolysis. This transient is assigned to 2 + on the basis of the pH dependence of the yields of products, and especially because of the correspondence of k 2(GS-):k s ratios measured directly with flash photolysis and by competition kinetics starting from the hydroxylaminoimidazole. The cation 2 + has a lifetime in water of 100 ms, and shows a high selectivity for GSH with k 2(GS-) = 3 × 107 M-1 s-1. There is evidence that this class of nitrenium ion is formed upon reductive metabolism of 2-nitroimidazoles. Thus this class of drugs is capable of producing a relatively long-lived electrophile in biological systems.

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Section: Discussionmentioning

confidence: 71%

Photochemistry of 2-Azido-1-methylimidazole in Aqueous Solutions. Observation of the 1-Methyl-2-imidazolylnitrenium Ion

and

McClelland

1999

J. Am. Chem. Soc.

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“…Starting Materials . Aniline and 4-(trifluoromethyl)-, 4-chloro-, 4-methoxy-, 4-(methylsulfanyl)-, 4-acetyl-, 2-(methylsulfanyl)-, and 2-iodoaniline were commercially available; 4-azidoaniline, 4-chloro-2-(methylsulfanyl)aniline, 5-chloro-2-(methylsulfanyl)aniline, and 2-(2-phenylethynyl)aniline were synthesized according to the literature. The corresponding diazonium tetrafluoroborates 7a − g were prepared following usual procedures…”

Section: Methodsmentioning

confidence: 99%

Cascade Radical Reactions via α-(Arylsulfanyl)imidoyl Radicals: Competitive [4 + 2] and [4 + 1] Radical Annulations of Alkynyl Isothiocyanates with Aryl Radicals

et al. 2003

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Aryl radicals react with 2-(2-phenylethynyl)phenyl isothiocyanate through a novel radical cascade reaction entailing formation of alpha-(arylsulfanyl)imidoyl radicals and affording a new class of compounds, i.e. thiochromeno[2,3-b]indoles. These derivatives are formed as mixtures of substituted analogues arising from competitive [4 + 2] and [4 + 1] radical annulations. The isomer ratio is strongly dependent on the aryl substituent and is correlated to its capability to delocalize spin density. The presence of a methylsulfanyl group in the ortho-position of the initial aryl radical results in complete regioselectivity and better yields, as the consequence of both strong spin-delocalization effect, which promotes exclusive [4 + 1] annulation, and good radical leaving-group ability, which facilitates aromatization of the final cyclohexadienyl radical. Theoretical calculations support the hypothesis of competitive, independent [4 + 2] and [4 + 1] annulation pathways. They also suggest that rearrangement onto the sulfur atom of the [4 + 1] intermediate does not occur via a sulfuranyl radical but rather through either a transition state or a sulfur-centered (thioamidyl) radical; the latter is possibly the preferred route in the presence of an o-methylsulfanyl moiety that can act as a leaving group in the final ipso-cyclization process.

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Synthesis and properties of poly(aniline-co-azidoaniline)

Jadhav

Gulgas

Guđmundsdóttir

2007

European Polymer Journal

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Rates of thermolysis of azidobenzenes in solution: large stabilizations of transition states by charge transfer from electron-donor substituents

Cited by 9 publications

References 17 publications

Photochemistry of 2-Azido-1-methylimidazole in Aqueous Solutions. Observation of the 1-Methyl-2-imidazolylnitrenium Ion

Photochemistry of 2-Azido-1-methylimidazole in Aqueous Solutions. Observation of the 1-Methyl-2-imidazolylnitrenium Ion

Cascade Radical Reactions via α-(Arylsulfanyl)imidoyl Radicals: Competitive [4 + 2] and [4 + 1] Radical Annulations of Alkynyl Isothiocyanates with Aryl Radicals

Synthesis and properties of poly(aniline-co-azidoaniline)

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