Furoxan rearrangement of some pyridofuroxan derivatives studied by1H,13C,14N,15N and17O NMR spectroscopy
作者:P. Cmoch、B. Kamie?ski、K. Kamie?ska-Trela、L. Stefaniak、G. A. Webb
DOI:10.1002/1099-1395(200008)13:8<480::aid-poc268>3.0.co;2-z
日期:2000.8
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.