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.
Die Reaktion von a-Chlorethern rnit klassischen Enolat-Anionen fuhrt nur dann zur glatten C -C-Verkniipfung, wenn letztere resonanzstabilisiert, also ,,weich" sind, so z. B. Natrium-Diethylmalonat sowie Enolate aus verwandten 1,3-Dicarbonylverbindungen ',*). Die Literatur enthalt praktisch keine analogen Beispiele fur ergiebige Alkylierungen von Enolaten aus gangigen Ketonen3). Tatsachlich ergibt die Reaktion von l a rnit 2-Chlortetrahydropyran 2a nur 43 T o des alkoxyalkylierten Produkts 3 als Diastereomerengemisch (ca. 3 : 2)4'. a-Acetoxyether wie 2b k0nnen gar nicht eingesetzt werden, da Enolat-Anionen rnit Estern Chisen-Kondensationen eingehen. Unter drastischen Bedingungen (1 10 -170°C) reagiert das Halbaminal 2c rnit Ketonen unter C -C-Verknupfung, allerdings mit sehr unterschiedlichem Erfolg, je nach der Natur der Carb~nylverbindung~). Die vorliegende Arbeit beschreibt eine einfache Ltlsung der hier angeschnittenen Probleme, ferner eine Anwendung bei der Synthese von C-Glycosiden.
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