Synthesis of Spin-Labelled 1,4-Dihydropyridines and Pyridines
作者:Olga H. Hankovszky、Cecilia P. Sár、Kálmán Hideg、Gyula Jerkovich
DOI:10.1055/s-1991-26389
日期:——
1,4-Dihydropyridines spin-labelled with 5- and 6-membered nitroxyl radicals in positions 1-4 of the pyridine ring were synthesized. The oxidation of these dihydropyridines to pyridines with active manganese dioxide was investigated.
group 2,2,6,6-tetramethylpiperidine-1-oxyl have been synthesized. A detailed EPR and ENDOR study of the neutral radicals and of their reduction products is reported. All the neutral species give EPR spectra consisting of a main triplet of lines with = 15 G splitting by the sup 14}N nucleus, typical of nitroxide radicals. Some of them show additional well-resolved splittings by methyl and methylene
The synthesis, electrochemical characterization and EPR study of a fulleropyrrolidine monoadduct, bearing two TEMPO groups differently linked at positions 2 and 5 of the pyrrolidine ring, are presented. The exchange interaction J between the two unpaired nitroxide electrons is of the same order of magnitude of the 14N hyperfine coupling (aN). EPR investigation in three different solvents showed that J decreases as the temperature increases. Chemical or electrochemical reduction produces a stable triradical anion that, in the case of chemical reduction, was characterized ia EPR spectroscopy. Further chemical reduction produces an unstable species probably corresponding to a protonated compound. The electrochemical study highlights an interesting effect of the fullerene moiety on the kinetics of TEMPO-centered electrochemical reduction, which was analyzed in the frame of Marcus theory of heterogeneous
electron transfer.
Synthesis and Dehydrobromination of α-Bromo Aldehyde and Ketone Nitroxyl Radical Spin Labels
作者:H. Olga Hankovszky、Kálmán Hideg、P. Cecilla Sár、M. Judit Lovas、Gyula Jerkovich
DOI:10.1055/s-1990-26788
日期:——
Various types of α-bromo aldehyde and ketone derivatives of nitroxyl radicals can be prepared in a selective bromination reaction with pyrrolidone hydrotribromide in the presence of a double bond. The saturated α-bromo aldehydes are dehydrobrominated with 1,8-diazabicyclo [5,4,0]undec-7-ene.