A series of α‐oxo‐iminoxyls was obtained by PbO2 oxidation of 4‐oximinoisoxazol‐5(4H)‐ones, 4‐oximinopyrazol‐5(4H)‐ones, and 1‐phenyl‐4‐oximino‐1,2,3‐triazol‐5(4H)‐one and characterized by electron spin resonance spectroscopy in conjunction with DFT calculations of structures, energies, and hyperfine coupling constants. The iminoxyls are σ‐radicals existing largely in the Z configuration with respect to the C=O group, but minor amounts of the E isomers were observable in several cases. Couplings of the free‐radical electron with N1, N2, N3, C4 and C5 ring nuclei as well as the imine nitrogen N6 were observed, and some isomers were also observed to couple with a CH3 group in position 3 and with the ortho‐H atoms of an aryl group in position 3. The lower energies of the Z isomers relative to the E isomers can be ascribed to a stabilizing interaction between a singly occupied orbital on the oxime oxygen and a lone pair orbital on the carbonyl oxygen.
6 = 3.8, dq (5-H), 3J4e,5.1= 2 Hz[~I]. Die massenspektrometrische Fragmentierung von ( 8 b ) entspricht dem von Vigevani et al.["I fur Methyl-3-N-acetyl-4-O-acetyl-~-daunosaminid angegebenen Muster.Versuche, rnit L-( +)-Weinsaure-dimethylester als Schutzgruppe haben gezeigt, daB nach der allylischen Aminierung eine Trennung in die Enantiomere moglich ist. Die Acetalisierung mit 2,3-Butandiol verlauft jedoch besser, so daB die Reaktionsfolge ( 3 ) -+ (7) bei Verwendung optisch aktiver Diole die Basis fur eine besonders leistungsfahige Synthese des D-oder L-Daunosamins sein sollte.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.