Polymer supported peracids

Two polymer-supported reagents have been developed for the oxidation of sulphoxides to sulphones these involve peracid groups150, and bound hypervalent metals activated by t-butyl hydroperoxide151,152. 

The oxidation of sulphoxides with peracid resins occurs rapidly and quantitatively at 20°C using dioxane as solvent150. Vanadium(V), generated on a polymer support by treatment of vanadium(IV) with a hydroperoxide (equation 49) may be used to oxidize successfully sulphoxides to sulphones in very good yields151. 

Pre-formed peracids used in the laboratory include 3-chloroperbenzoic acid,111 which is long established in synthesis, and magnesium monoperoxy-phthalate.112 Polymer-supported percarboxylic acids have also been prepared for organic synthesis purposes (Figure 2.39).113... 

Polymer-supported peracids are also used effectively for the epoxidation of di-and trisubstituted olefins. The ratio of the stereoisomers is similar to that for the products of the reaction of the monomer with aromatic peracids. MCPBA epoxidation of homoallyl phosphonates has led to the preparation of 3,4-epoxyalkane phosphonates 39 in addition to the 1,2- and 2,3-epoxy derivatives.Stereospecific peracid oxidation is one of the preparative methods employed in the synthesis of the structurally varied cyclic polyoxirane isomers, which are of interest from a biological aspect. ... 

A method for the polymer supported epoxidation of olefins has been reported <05TL1643>. The resin supported phthalate, 11, was oxidized to peracid 12 through oxidation with or a urea-HjOj complex. The reaction was most conveniently carried out by mixing 11, the urea-HPj complex and the olefinic substrate. Simple filtration then provides a wide variety of epoxides in excellent yield. This reagent system provides all of the typical advantages of supported reagents as well as an improved safety profile of the supported peracid. 

Polymer-supported reagent. A polymeric peracid reagent (1) has been prepared from a polystyrene resin cross-linked with 1 or 2% of divinylbenzene by chloromethylation and oxidation to give a resin substituted by carboxyl groups. The —COOH groups are then converted into —COOOH groups by treatment... 

Olefins, including medium-ring cyclic olefins, have been epoxidized using a polymer supported peracid, thus cis-cyclo-octene was epoxidized in 95% yield. Agerol (293) has been converted into ageratriol (294) by two routes, epoxidation and base promoted isomerization, and photosensitized oxidation followed by sodium boro-hydride reduction. ... 

Peracids.—Acyl chlorides have been converted into peracids, in ca. 60% yields, by treatment with hydrogen peroxide and pyridine the precise amount of the latter used is crucial to the success of the method. Two reports have appealed on the preparation and uses of polymer supported peracids detailing their application in the epoxidation of olefins, and the oxidation of sulphides, notably penicillins to the corresponding sulphoxides. a-Hydroperoxy acids are available in high yield by addition of oxygen to lithium enolates at -100 °C. 

It has been stated numerous times that polymer-bound reactive intermediates are more stable than the corresponding solubilised counterparts. The stabilisation forces exerted by the polymeric matrix are most probably due to hydrophobic clustering. Polymer-bound peracids are believed to be more stable and not explosive. - The hydrophobic nature of polystyrene resins in combination with the high dilution effect has been used successfully several times to accelerate intramolecular cyclisations by grafting molecules onto a solid support as shown in Chapter 7.6.2>>22... 

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