Selenium‐Promoted Oxidation of Organic Compounds: Reactions and Mechanisms

Abstract

Oxidation reactions are fundamental processes widely applied in organic synthesis. Elemental selenium and more often its compounds have been successfully used as stoichiometric reagents and catalysts for oxidation of different organic substrates. Selenium(IV) oxide, areneseleninic acids and their anhydrides are widely used as stoichiometric oxidants or as oxygen‐transfer agents for oxygen donors, particularly hydrogen peroxide and tert‐butyl hydroperoxide. Organic diselenides (the precursors of seleninic acids) have been used as oxidation catalysts while dimethyl and diphenyl selenoxides are stoichiometric oxidants. Selenenamides, such as 2‐phenyl‐1,2‐benzisoselenazol‐3(2H)‐one (ebselen) and its analogues, known as glutathione peroxidase mimics acting via active hydroperoxide intermediates, are efficient and selective oxidation catalysts. Selenium(IV) oxide and some organoselenium compounds have been successfully applied for various oxidations useful in practical organic syntheses such as epoxidation, 1,2‐dihydroxylation, and α‐oxyfunctionalization of alkenes as well as for ring contraction of cycloalkanones, conversion of halomethyl, hydroxymethyl, or active methylene groups into formyl groups, oxidation of aldehydes into carboxylic acids, sulfides into sulfoxides, and secondary amines into nitrones, regeneration of parent carbonyl compounds from their azomethine derivatives and for other reactions. The oxidation mechanisms depend on the substrate and oxidant or catalyst used. The electrophilic center localized on the selenium atom or the nucleophilic center localized on the oxygen atom of the selenahydroperoxide group are involved in the reaction mechanism. In both cases the selenium‐containing moiety is a good leaving group. Exceptionally oxidation can proceed via free radical selenium species. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Epoxidation of cyclooctene and cyclohexene with hydrogen peroxide catalyzed by bis[3,5-bis(trifluoromethyl)-diphenyl] diselenide: Recyclable catalyst-containing phases through the use of glycerol-derived solvents

“…Moreover diselenides can be easily oxidized in situ by hydrogen peroxide to seleninic acid or peroxyseleninic acid, which are in some cases excellent catalysts in the oxidation of organic compounds [21][22][23][24], as, for instance, epoxidation reaction of alkenes [25], Baeyer-Villiger reaction [26], oxidation of carbonyl compounds [27], dehydrogenation of carbonyl compounds [28][29], oxidation of secondary amines [30][31], oxidation of imines [32], or selenenylations or halogenations [33].…”

A novel porphyrazine ligand tailored to homogeneous metal catalyzed transformations

“…Melting point determinations were performed by using a Gallenkamp melting point apparatus. 1 H NMR (400 MHz) and 13 C NMR (100 MHz) were recorded on Bruker AV400 spectrometer; chemical shifts …”

“…Thus, a survey of oxidants was undertaken and on treatment of 2 with freshly sublimed SeO 2 (2.5 equiv) in refluxing 1,4-dioxane for 7 h, clean tandem oxidation/N-decarbamoylation pleasingly ensued to produce 3 in 90% yield. 13,14 This compound precipitates directly from the reaction mixture as orange solid so that this process proved useful enough to prepare multigram quantities of 3. In the approach to 3, alternatives to Scheme 2 were examined which proved less successful or less direct.…”

Diaryl diselenides and benzisoselenazol-3(2H)-ones as oxygen-transfer agents

“…Starting with the introduction of solid-phase peptide synthesis by Merrifield, insoluble supports have been implemented in a wide range of synthetic methodologies. [56][57][58] Athough a variety of selenium compounds have been used during the last three decades as stoichiometric oxidants or oxygen transfer catalysts 59 to our knowledge only one of them (polyester resin containing oxyselenium groups) has been used as an oxidant for conversion of benzyl, allyl and active alkyl bromides to aldehydes 60 and a second one (polystyrene-supported benzeneseleninic acid) as a catalyst for TBHP oxidation of benzyl and allyl alcohols to aldehydes and phenols to quinones. Other polymer-supported benzisoselenazol-3(2H)-one is MONICAT C (100) obtained by acylation-selenenylation of primary amino groups in 1-aminohexylamine gel with dichloride (89) while the aminoebselen (101) was a substrate for synthesis of benzisoselenazol-3(2H)-one supported on Merrifield resin MONICAT D (102) as shown in Scheme 23.…”