Oximes represent one of the fundamental organic compound classes with a wide range of synthetic applications. In the last decade O-substituted oximes were recognized as the synthetically available and versatile precursors of iminyl radicals via one-electron oxidation or one-electron reduction employing visible light photoredox catalysts, salts of abundant metals (such as Cu or Fe), or other convenient reagents. Iminyl radicals are powerful synthons for various processes of cyclization, ringopening, CH-functionalization, and coupling. The present review is focused on the synthetic methods based on oxime-derived iminyl radicals developed in the last few years excluding ring opening reactions of cyclic iminyl radicals that were summarized in recent publications. The review consists of two main parts:(1) reactions of iminyl radicals involving 1,n-hydrogen atom transfer (n = 5 in most cases) and (2) reactions involving the addition of iminyl radical to the carbon-carbon π-bond.
The development of new types of fungicides for agriculture and medicine is highly desirable due to the uprising fungal resistance against commonly used compounds. Herein, 4-substituted-4-nitropyrazolin-5-ones (nitropyrazolones) were proposed as highly active fungicides of the novel structural type. The first scalable and practical method for the nitropyrazolone synthesis was proposed, which is atom-efficient, is applicable for the multigram scale synthesis, and allows for production of a wide variety of nitropyrazolones with high yields and purity. The synthesized compounds demonstrated high fungicidal activity against the broad spectrum of phytopathogenic fungi (Venturia inaequalis, Rhizoctonia solani, Fusarium oxysporum, Fusarium moniliforme, Bipolaris sorokiniana, and Sclerotinia sclerotiorum). Their mycelium growth inhibiting activity was comparable or superior to that of kresoximmethyl. In vitro activity against Staphyloccocus aureus, Candida albicans, and Aspergillus niger revealed that nitropyrazolones are promising candidates against human pathogens. The key factors for the manifestation of high fungicidal activity were established to be an aromatic substituent on the N1 atom and small substituents, such as methyl, at the C3 and C4 positions of the pyrazolone ring.
Electrochemically induced radical‐initiated reaction of vinyl azides with N‐hydroxyphthalimide resulting O‐phthalimide oximes with challenging for organic chemistry N−O‐N fragment has been discovered. The developed approach introduces in synthesis electrochemically generated O‐centered imide‐N‐oxyl radicals as the coupling components. Sequential formation of C−O and N−O bonds was achieved via generation and selective addition of imide‐N‐oxyl radicals, followed by recombination with iminyl radicals. A wide range of O‐phthalimide oximes was obtained with the yields up to 84%.
The reactivity of CH-acidic and structurally related enol-containing heterocycles towards N-oxyl radicals was disclosed. Traditionally, these substrates were considered as reactants for ionic transformations. Highly selective and efficient N-oxyl radical mediated C–O coupling of substituted barbituric or Meldrum’s acids with N-hydroxy compounds (N-hydroxyimides, hydroxamic acids, oximes, and N-hydroxybenzotriazole) was achieved using inexpensive manganese-containing salts as oxidants. Metal-free C–O coupling was demonstrated using diacetyliminoxyl as both the oxidant (hydrogen atom acceptor) and the coupling partner.
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