Peroxidation of β-diketones and β-keto esters with tert-butyl hydroperoxide in the presence of Cu(ClO4)2/SiO2

Electrochemical Generation of Peroxy Radicals and Subsequent Peroxidation of 1,3-Dicarbonyls in an Undivided Cell

The generation of peroxy radicals from hydroperoxides with subsequent selective peroxidation of 1,3-dicarbonyls in an undivided electrochemical cell under constant current conditions is reported. The method provides a variety of peroxy-containing barbituric acids and 4-hydroxy-2(5H)-furanones with yields of up to 74%. Only the combination of anodic and cathodic processes provides efficient peroxidation by generating a set of alkoxy and peroxy radicals. NaNO3 acts as both an electrolyte and a redox mediator of radical reactions.

Oxidative α-acyloxylation of acetals with cyclic diacyl peroxides

Selective functionalization of the non-activated acetal α-position with formal retaining of the acetal fragment was realized using cyclic diacyl peroxides.

Oxime radicals: generation, properties and application in organic synthesis

N-Oxyl radicals (compounds with an N-O• fragment) represent one of the richest families of stable and persistent organic radicals with applications ranging from catalysis of selective oxidation processes and mechanistic studies to production of polymers, energy storage, magnetic materials design and spectroscopic studies of biological objects. Compared to other N-oxyl radicals, oxime radicals (or iminoxyl radicals) have been underestimated for a long time as useful intermediates for organic synthesis, despite the fact that their precursors, oximes, are extremely widespread and easily available organic compounds. Furthermore, oxime radicals are structurally exceptional. In these radicals, the N-O• fragment is connected to an organic moiety by a double bond, whereas all other classes of N-oxyl radicals contain an R2N-O• fragment with two single C-N bonds. Although oxime radicals have been known since 1964, their broad synthetic potential was not recognized until the last decade, when numerous selective reactions of oxidative cyclization, functionalization, and coupling mediated by iminoxyl radicals were discovered. This review is focused on the synthetic methods based on iminoxyl radicals developed in the last ten years and also contains some selected data on previous works regarding generation, structure, stability, and spectral properties of these N-oxyl radicals. The reactions of oxime radicals are classified into intermolecular (oxidation by oxime radicals, oxidative C-O coupling) and intramolecular. The majority of works are devoted to intramolecular reactions of oxime radicals. These reactions are classified into cyclizations involving C-H bond cleavage and cyclizations involving a double C=C bond cleavage.

Catalyst Development for the Synthesis of Ozonides and Tetraoxanes Under Heterogeneous Conditions: Disclosure of an Unprecedented Class of Fungicides for Agricultural Application

The catalyst H_3+x PMo_12-x ⁺⁶ Mo_x ⁺⁵ O₄₀ supported on SiO₂ was developed for peroxidation of 1,3- and 1,5-diketones with hydrogen peroxide with the formation of bridged 1,2,4,5-tetraoxanes and bridged 1,2,4-trioxolanes (ozonides) with high yield based on isolated products (up to 86 and 90 %, respectively) under heterogeneous conditions. Synthesis of peroxides under heterogeneous conditions is a rare process and represents a challenge for this field of chemistry, because peroxides tend to decompose on the surface of a catalyst . A new class of antifungal agents for crop protection, that is, cyclic peroxides: bridged 1,2,4,5-tetraoxanes and bridged ozonides, was discovered. Some ozonides and tetraoxanes exhibit a very high antifungal activity and are superior to commercial fungicides, such as Triadimefon and Kresoxim-methyl. It is important to note that none of the fungicides used in agricultural chemistry contains a peroxide fragment.

Silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with malonyl peroxides in solvent-free conditions

For the first time silica gel was observed to activate peroxides in oxidative coupling reactions. Here we report silica gel mediated oxidative C–O coupling of β-dicarbonyl compounds with cyclic diacyl peroxides affording α-acyloxy derivatives with 100% atom efficiency. The highest yields of coupling products were achieved in solvent free conditions. C–O coupling products were prepared in yields up to 86%.