4440-33-9Relevant articles and documents
Generation and characterization of the selenocysteinyl radical: Direct evidence from time-resolved UV/Vis, electron paramagnetic resonance, and fourier transform infrared spectroscopy
Kolano, Christoph,Bucher, Goetz,Schade, Olaf,Grote, Dirk,Sander, Wolfram
, p. 6609 - 6615 (2007/10/03)
The selenocysteinyl radical 1 has been generated for the first time by laser flash photolysis (λexc = 266 nm) of dimethyl bis(N-tert-butoxycarbonyl)-L-selenocystine 2 and of [(9-fluorenylideneamino)- oxycarbonyl]methyl(N-tert-butoxycarbonyl)-L-selenocysteine 3 in acetonitrile and characterized by time-resolved (TR) UV/Vis, Fourier transform infrared (FTIR), and electron paramagnetic spectroscopy in combination with theoretical methods. A detailed product study was conducted using gas chromatography and one- and two-dimensional NMR spectroscopy. In the case of [(9-fluorenylideneamino) oxycarbonyl]methyl(N-tert-butoxycarbonyl)-L-selenocysteine 3, the (9-fluorenylideneamino)oxycarbonyl moiety serves as a photolabile protection group providing a caged selenocysteinyl radical suitable for biophysical applications. Cleavage of the diselenide bridge or the selenium-carbonyl bond by irradiation is possible in high quantum yields. Because of the lack of a good IR chromophore in the mid-IR region, the selenocysteinyl radical 1 cannot be monitored directly by TR FTIR spectroscopy. TR UV/Vis spectroscopy revealed the formation of the selenocysteinyl radical 1 from both precursors. The selenocysteinyl radical 1 has a lifetime τ ≈ 63 μs and exhibits a strong band located at λmax = 335 nm. Calculated UV absorptions of the selenocysteinyl radical (UB3LYP/6-311G(d,p)) are in good agreement with the experimental results. The use of TR UV/Vis spectroscopy permitted the determination of the decay rates of the selenocysteinyl radical in the presence of two quenchers. The product studies demonstrated the reversible photoreaction of dimethyl bis(N-tert-butoxycarbonyl) -L-selenocystine 2. Products of the photolysis of the caged selenocysteinyl radical precursor 3 are dimethyl bis(N-tert- butoxycarbonyl)-L-selenocystine 2, carbon dioxide, and some further smaller fragments. In addition, the photo-decomposition of the (9-fluorenylideneamino) oxycarbonyl moiety produced 9-fluorenone-oxime 4, 9-fluoren-imine 5, and 6 and 7 as products of the dimerization of two 9-fluorenoneiminoxy radicals 8.
Thermolyses of O-Phenyl Oxime Ethers. A New Source of Iminyl Radicals and a New Source of Aryloxyl Radicals
Blake, Jessie A.,Pratt, Derek A.,Lin, Shuqiong,Walton, John C.,Mulder, Peter,Ingold
, p. 3112 - 3120 (2007/10/03)
Six O-phenyl ketoxime ethers, RR′C=NOPh 1-6, with RR′= diaryl, dialkyl, and arylalkyl, together with N-phenoxybenzimidic acid phenyl ether, PhO(Ph)C=NOPh, 7, have been shown to thermolyze at moderate temperatures with "clean" N-O bond homolyses to yield iminyl and phenoxyl radicals, RR′C=N. and PhO.. Since 1-6 can be synthesized at room temperature, these compounds provide a new and potentially useful source of iminyls for syntheses. The iminyl from 7 undergoes a competition between β-scission, to PhCN and PhO., and cyclization to an oxazole. Rate constants, 106 k/s-1, at 90 °C for 1-6 range from 4.2 (RR′ = 9-fluorenyl) to 180 (RR′ = 9-bicyclononanyl), and that for 7 is 0.61. The estimated activation enthalpies for N-O bond scission are in satisfactory agreement with the results of DFT calculations of N-O bond dissociation enthalpies, BDEs, and represent the first thermochemical data for any reaction yielding iminyl radicals. The small range in k (N-O homolyses) is consistent with the known σ structure of these radicals, and the variations in k and N-O BDEs with changes in RR′ are rationalized in terms of iminyl radical stabilization by hyperconjugation: RR′C=N . ? R.R′C≡N. Calculated N-H BDEs in the corresponding RR′C= NH are also presented.
Electrochemical reduction of oximes in aprotic media
Soucaze-Guillous, Benoit,Lund, Henning
, p. 417 - 424 (2007/10/03)
The electrochemical reduction in N,N-dimethylformamide of (Z)- and (E)-benzaldoximes, derivatives thereof and some ketoximes has been investigated. The bases electrogenerated during the reduction of the benzaldoximes and their derivatives induce a catalytic elimination reaction producing benzonitrile. Two mechanisms are discussed, one in which the electrogenerated base eliminates water from the incoming substrate and one in which the base abstracts a proton from the intermediate benzaldimine radical with formation of benzonitrile radical anion; this radical anion then reduces the incoming substrate. The electrogenerated base formed during the reduction of the ketoximes deprotonates the oxime to the less reducible oxime anion. During the reduction of an acylated oxime, the parent oxime is formed, probably by cleavage induced by the electrogenerated base, but direct cleavage of the radical anion to the oxime might be possible. Acta Chemica Scandinavica 1998.
