Green Chemistry with Selenium Reagents: Development of Efficient Catalytic Reactions

Abstract

cyclizations · homogeneous catalysis · oxidation · seleniumApplications of selenium reagents in organic chemistry have developed rapidly over the past years, and comprehensive reviews on this area have appeared.[1] Rather new, however, is the use of selenium-based catalysts in organic synthesis. We highlight new developments in organoselenium catalysis and in particular the use of selenium electrophiles and organoselenium compounds in carbonylation reactions and the oxidation of alkenes and carbonyl compounds. The use of organoselenium ligands for metal-catalyzed processes is not covered here; the topic has been reviewed recently elsewhere.[1f] Also their potential as efficient mimetics for selenoenzymes will not be discussed. [2] In this Highlight we will focus on the catalytic use of selenium electrophiles for selenenylations and halogenations as well as the use of perseleninic acids as catalytic oxidants for various substrates.The use of electrophilic selenium reagents is a very versatile strategy for functionalizing alkenes 1. To avoid the use of stoichiometric amounts of selenium reagents, researchers have sought for analogous catalytic methods. Selenenylation-deselenenylation sequences involve two steps: the initial selenofunctionalization is followed by oxidation of the organoselenium moiety in 2, which allows the regeneration of the reagent through b elimination giving 3 or substitution to provide 4 (Scheme 1). Various reagents can be used to activate the selenide moiety in 2 to undergo elimination or substitution. The most explored approach involves oxidation with an excess of persulfate.[3] The oxidant is initially responsible for the generation of the electrophilic selenenylating agent from the corresponding diselenide and then for the oxidation of the selenium moiety in 2 allowing the regeneration of the catalyst. This approach proved to be useful for functionalizations such as hydroxylations, alkoxylations, and cyclizations, and when chiral nonracemic diselenides were used, interesting levels of stereoselectivity were reached. [3] Depending on the substrate 5, either an addition-elimination sequence to yield 6 or a cyclization-elimination sequence to give 7 is possible by using an electrochemical procedure (Scheme 2).[4] The reaction is initiated by anodic oxidation of bromide to bromine. The latter reacts with the diselenide to afford the arylselenenyl bromide, which promotes the selenofunctionalization. Subsequent elimination of the selenium moiety via a tetravalent selenium compound gives the products 6 or 7 and regenerates the arylselenenyl bromide. Alternatively, hypervalent iodine reagents such as [bis(trifluoroacetoxy)iodo]benzene can be used as oxidants, in combination with catalytic amounts (5 mol %) of diselenides, to effect the conversion of butenoic acids 5 (R = H) to the corresponding butenolides 7 in yields of up to 95 %.[5] In a diselenide-catalyzed dihydroxylation of alkenes with ammonium persulfate as the oxidant both nucleophiles are hydroxy groups and diols of type 4 (Nu = Nu' =...

Synthesis of new alkylated and methoxylated analogues of ebselen with antiviral and antimicrobial properties

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] Due to their unique properties, they attracted a wide interest as reagents in new synthetic routes, 3 promising catalysts for various oxidation reactions [1][2][3][4][5][6][7][16][17][18][19] and potential pharmaceuticals. [8][9][10][11][12][13][14][15]20,21 Ebselen (2-phenylbenzisoselenazol-3(2H)-one) and its analogues have received particular attention as glutathione peroxidase mimics, 8,11,15 antioxidant and anti-inflammatory agents.…”

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].…”

Water and Aqueous Mixtures as Convenient Alternative Media for Organoselenium Chemistry

“…Even if the use of inorganic selenoxide (SeO2) for the catalytic allylic oxidation of olefins was reported by Sharpless in 1977 [45] and it was later demonstrated that the same catalyst, in the presence of hydrogen peroxide as an oxidant in a mixture of water and dioxane, can convert olefins into the corresponding diols [46], it was only in 2009 that the use of organoselenium catalysts was, for the first time, claimed as a convenient, green alternative to conventional stoichiometric protocols or metal-catalyzed reactions [47]. These opened the way for a series of applications designed in order to address the principle of Green Chemistry, and a number of interesting results obtained during the last five years were recently collected in a review article [1].…”