Pyridofuroxan ([1,2,5]oxodiazolo[3,4-b]pyridine 1-oxide) undergoes isomerization between the N1-oxide and N3-oxide forms which can be observed by the H-1, C-13 and N-15 NMR spectroscopy but not by N-14 and O-17 NMR at ambient and low temperatures. The rearrangement becomes slower at low temperatures and at 233 K H-1 NMR signals for the two structures become observable. H-1, C-13 and N-15 chemical shifts and H-1-H-1, C-13-H-1 and C-13-C-13 coupling constants are used to characterize both forms in the equilibrium mixture. From the H-1 NMR integrals at 233 K equilibrium constants are calculated. Protonation studies using trifluoroacetic acid as a solvent showed the favoured site of protonation to be the pyridine N4 nitrogen atom. DFT shielding calculations are reported for the C-13, N-15 and O-17 nuclei which support the assignments given. From the point of view of structural changes, (1)J(CC) data for 8-nitrotetrazolo[1,5-a]pyridine and o-nitroaminopyridine as precursors of the pyridofuroxans are given for comparison purposes. X-ray diffraction data on 5-methoxypyridofuroxan support the structural results obtained from the NMR investigations. Copyright (C) 2000 John Wiley & Sons, Ltd.
Facile One-Pot Synthesis of 2,1,3-Benzoxadiazole<i>N</i>-Oxide (Benzofuroxan) Derivatives Under Phase-Transfer Catalysis
作者:N. R. Ayyangar、S. Madan Kumar、K. V. Srinivasan
DOI:10.1055/s-1987-28023
日期:——
Several 2,1,3-benzoxadiazole N-oxide (benzofuroxan) derivatives are synthesized from the corresponding o-chloronitrobenzenes in a one-pot operation by stirring with sodium azide in dichloroethane in the presence of benzyl tributylammonium bromide as a phase-transfer catalyst. The moderate reaction conditions enable the isolation of the intermediate reactive azido compounds.
ions. Such a ranking holds promise for expanding the range of couplingreactions which can be envisioned with such strongly electron-deficient neutral heteroaromatics as nitrobenzofuroxans and related compounds. Arguments are also given which exclude the possibility for the reactions studied to proceed via an electron-transfer mechanism.
Dual Behavior of 4-Aza-6-nitrobenzofuroxan. A Powerful Electrophile in Hydration and σ-Complex Formation and a Potential Dienophile or Heterodiene in Diels−Alder Type Reactions
作者:F. Terrier、M. Sebban、R. Goumont、J. C. Hallé,、G. Moutiers、I. Cangelosi、E. Buncel
DOI:10.1021/jo0005114
日期:2000.11.1
found to be a versatile Diels-Alder reagent, as a result of the low aromatic character of its six-membered ring. Upon treatment of 2 with cyclopentadiene and 2,3-dimethylbutadiene, various reactivity patterns have been observed. These led to different cycloadducts arising from normal as well as inverse electron-demand condensations involving the pyridine ring as the dienophile or the heterodiene contributor
Synthesis of stable adducts of highly electrophilic nitro(het)arenes with С-nucleophiles
作者:A. M. Starosotnikov、M. A. Bastrakov、V. A. Kokorekin
DOI:10.1007/s11172-022-3435-0
日期:2022.3
The reaction of highly electrophilic azolo[b]pyridines with pyrrole and indole derivatives as nucleophiles afforded 1,4-addition products to the pyridine ring. The reactions of structurally similar meta-dinitrobenzo-fused heterocycles (furoxan, thiadiazole, selenadiazole, pyridine) with C-nucleophiles (salts of ketones and 2-nitropropane) gave stable anionic σ-complexes in high yields. Their oxidation led to rearomatization with the formation of the corresponding products of substitution of a hydrogen atom with the nucleophile. The oxidation was generally accompanied by the decomposition of σ-complexes into the parent compounds.
Diels–Alder trapping of an o-dinitroso intermediate in the 1-oxide/3-oxide interconversion of a 2,1,3-benzoxadiazole derivative
作者:Muriel Sebban、Régis Goumont、Jean Claude Hallé、François Terrier、Jérome Marrot
DOI:10.1039/a902170a
日期:——
Convincing evidence is presented that the o-dinitroso intermediate involved in the exchange of the 1-oxide and 3-oxide tautomers of 6-nitro[2,1,3]oxadiazolo[4,5-b]pyridine 1-oxide 5 is the precursor of the DielsâAlder diadduct 7 isolated upon treatment of this compound with cyclohexadiene in CHCl3.