Epoxidation by oxone

Wang and Shi have published a detailed study of their fructose-based dioxirane epoxidation catalyst system with hydroxyalkene substrates. The ees obtained were highly pH dependent. The lower enantioselectivity obtained at low pH is attributed to the substantial contribution of direct epoxidation by Oxone. The results obtained with... 

A. Armstrong, G. Ahmed, 1. Garnett, K. Goacolou, Pyrrolidine-Derived iminium salts as catalysts for alkene epoxidation by Oxone , Synlett (1997) 1075. 

Armstrong has shown that even acyclic iminium salts can mediate epoxidation by Oxone [73] however, enantiomeric excesses are low [74]. By condensing A-trimethylsilylpyrrolidine 23 with a range of aromatic aldehydes in the presence of trimethylsilyltriflate, Armstrong was able to produce a range of substituted exocyclic iminium salts (Scheme 1.28). 

The simplest model compound is cyclohexene oxide III. Monomers IV, V and VII represent different aspects of the ester portion of I, while monomers VII and VIII reflect aspects of both the monomer I and the polymer which is formed by cationic ring-opening polymerization. Monomers IV-VII were prepared using a phase transfer catalyzed epoxidation based on the method of Venturello and D Aloisio (6) and employed previously in this laboratory (7). This method was not effective for the preparation of monomer VIII. In this specific case (equation 4), epoxidation using Oxone (potassium monoperoxysulfate) was employed. 

Several efficient procedures for alkene epoxidation using Oxone were reported, such as Oxone/aqueous NaOH, Oxone/acetone, Oxone/water , Oxone/PTC/benzene/ aqueous buffer solution or Oxone/2-butanone system. Thus, sorbic acid can be regioselectively oxidized using Oxone/aqueous NaOH to 4,5-epoxy-2-hexenoic acid in 84% yield. Similarly, cyclooctene is oxidized to cyclooctene oxide in 81% yield, just by stirring it with Oxone in water . 1-Dodecene is epoxidized in good yield by Oxone/PTC in benzene aqueous buffer solution. It is otherwise difficult to epoxidize 1-dodecene by other oxidizing reagents. ... 

Chiral dioxirane that was also generated in situ from the corresponding ketone and Oxone was first used for catalytic asymmetric epoxidation by Curd et al., although enantioselectivity was low [7], Later, Yang et al. disclosed that this approach had a bright prospect if used with a combination of Oxone and chiral ketone 3 [8]. Ketone 3 is converted into the corresponding dioxirane in situ, which epoxidizes olefins (Scheme 6B.5). 

Another immobilized system was recently reported by Wei and Liu [64] using amphiphilic coblock polymers consistent of ethylene glycol and methyl acrylate monomers that had been functionalized with imidazole groups. In combination with oxone (KHS05) as the oxidant in an ethyl acetate/water mixture, this system yields the 1,2-diol product in 62% yield, which is probably formed by ring opening of the epoxide by the acidic oxone. 

Ketones can be converted to dioxiranes by Oxone (2KHSO5 KHSO4 K2SO4) under shghtly alkaline conditions (pH 7-8) (400). The dioxirane of 1,1,1-trifluoroacetone is a powerful yet selective oxidant under mild conditions, typically at temperatures below 313 K (10). Exemplary reactions are stereospecific olefin epoxidation and hydroxylation of tertiary C-H groups, or ketonization of CH2 groups. With chiral ketones, even enantioselective reactions are possible (401). Although the reactions are often performed in excess ketone, it is actually possible to use the ketone in a catalytic fashion, for example, for 1,1,1-trifluoroacetone (Scheme 5). 

Reaction of racemic 1,2-diazocinone 2 with (S)-(—)-iV-(methoxymethyl)proline methyl ester, followed by crystallization from MeCN, gave the diastereomer (R,S,S)-(+)366-S <2004TA537>. The diazocinone 37a was subjected to epoxidation conditions (oxone, acetone, NaHCO() and subsequent deprotection of the Ar-carbobcnzyloxy moieties with Pd/C-H2 to give 38. 

Dioxiranes, prepared from acetone and other aliphatic ketones by treatment with Oxone, can accomplish oxidations that are usually not achieved by Oxone itself [210, 211], Dioxiranes can be isolated by vacuum codistillation with the respective ketones [210], or else, they may be formed in situ and applied in the same reaction vessel [210, 211]. Examples of the applications of dioxiranes are epoxidations 210] and the oxidation of primary amines to nitro compounds [211], of tertiary amines to amine oxides [210], and of sulfides to sulfoxides [210] (equation 12). 

As shown in the Table, with 5 mol% of 1,1-dioxotetrahydrothiopyran-4-one as catalyst,10 epoxidation of various olefins (2-mmol scale) in a homogeneous acetonitrile-water solvent system with 1.5 equiv of Oxone at room temperature can be achieved in a short period of time with excellent yields of epoxides (80-97%) isolated by flash column chromatography.2 As the pH of the reaction is maintained at 7-7.5 by sodium bicarbonate, acid- or base-labile epoxides (entries 12-14) can be easily isolated without decomposition. More importantly, the in situ epoxidation of olefins can be performed on a large scale directly with 5 mol% of tetrahydrothiopyran-4-one, which is oxidized immediately by Oxone to 1,1-dioxotetrahydrothiopyran-4-one during the epoxidation reactions. For example, with 5 mol% of tetrahydrothlopyran-4-one, substrates 3,5 (20 mmol each) and 11 (100 mmol) were epoxidized with excellent isolated yields of epoxides (91-96%). 

SCHEME 5.21 The standard conditions applied for catalytic asymmetric epoxidation mediated by Oxone and iminium salts. 

L. Bohe, M. Kammoun, Catalytic oxaziridinium-mediated epoxidation of olefins by Oxone . A convenient catalyst excluding common side reactions. Tetrahedron Lett. 43 (2002) 803. 

Ketones represented by 83 are a new gencr epoxidation of alkenes by Oxone . Ketone epoxidation of cw-alkenes. For example, double bond. 

Several cyclodextrin ketones with a ketone attached to the secondary face of the cyclodextrin in the form of a 2,3-0-( 1,3-acetone) group (79), and some selected cyclodextrin ketones having the ketone at the primary face, were investigated for their catalysis of epoxidation of stilbenes and styrene by oxone in 1 1 acetonitrile/H20. It was found that secondary face ketones were better catalysts giving a cat uncat over 10, and more stereoselective giving up to 76% ee in (5)-styrene oxide. ... 

DFT calculations at UB3LYP/6-31G(d,p), /6-31+G(d) or 6-31G-b(d,p) level and spectrometry analysis of enantioselective chiral amine-catalysed olefin epoxidation by H2O2 or oxone in MeCN-H20 (95 5) in the presence of NaHCOj suggest that the amine is first oxidized to nitroxide radical which is further oxidized to A,A(-dioxo-radical which is the effective oxidant for epoxide formation. The calculations also explain the formation of a large amount of diol during the epoxidation reaction A(,A(-dioxo-radical is protonated by HC03, and this protonated radical easily oxidizes olefin into diol. Pyridine suppresses the formation of diol because it suppresses the protonation of tV,tV-dioxo-radical." ... 

Shi s chiral ketone (21) catalyses the asymmetric epoxidation of 2,2-disubstituted vinylsilanes by Oxone. Enantioselectivity is presumed to be better when the spiro, rather than the planar, transition state is operating. This is probably favoured when the 2-substituents are less bulky and the planar transition-state is disfavoured by bulky silyl substituents. ... 

The water-soluble weso-tetrakis(4-JV-methylpyridyl)porphinatoman-ganese(lll) chloride efficiently catalyzes (2 m in at r.t., 99% conversion) the epoxidation of sodium 4-styrenesulfonate by oxone (a stable water-soluble oxidant with the approximate composition K2S04 2KHS05 KHS04) in water at neutral pH [15]. In the absence of catalyst, the reaction time is ca. 10 times longer. 

The synthetic route of sulfite-linked cycloaliphatic epoxy resin is presented in Figure 8.13 [38]. The synthesis of intermediate is achieved via the nucleophilic substitution reaction of thionyl chloride with cyclohex-3-enyl-1-methanol. Subsequently, Epo-S is obtained by epoxidation with OXONE oxidant. Epo-S is liquid at room temperature which is favorable for the underfilling encapsulation for high-density electronic packaging technologies such as flip chip plastic ball grid array (FC-PBGA) and MCM. 

Furthering this work, Denmark produced a range of 0x0 bis(ammonium) salts to enhance the electrophilicity of the carbonyl carbon and it was hoped this would eliminate the Baeyer-Villiger reaction. The first two attempts resulted in no formation of epoxide in the oxidation reaction. Oxone decomposition studies revealed that the catalysts were rapidly destroyed by oxone. 

The pollutant (xenobiotic) forms a stable covalent bond with its target. Examples include the phosphorylation of cholinesterases by the oxon forms of OPs, the formation of DNA adducts by the reactive epoxides of benzo[a] pyrene and other PAHs, and the binding of organomercury compounds to... 

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