Epoxides, vinyl cleavage

However, unlike the triaryIsulfonium salts, these compounds undergo reversible photoinduced ylid formation rather than homolytic carbon-sulfur bond cleavage. Because the rate of the thermal back reaction is appreciable at room temperature, only those monomers that are more nucleophilic than the ylid will polymerize. Epoxides, vinyl ethers, and cyclic acetals undergo facile cationic polymerization when irradiated in the presence of dialkylphenacylsulfonium salts as photoinitiators. 

Vinyl epoxides (vinyloxiranes) are reactive allylating agents. The oxidative addition of Pd(0) to the vinyl epoxides with cleavage of the epoxide ring occurs to generate... 

A retrosynthetic analysis of fragment 152 can be completed through cleavage of the C16-C17 bond in enone 155, the projected precursor of epoxide 152. This retrosynthetic maneuver furnishes intermediates 156 and 157 as potential building blocks. In the forward sense, acylation of a vinyl metal species derived from 156 with Weinreb amide 157 could accomplish the construction of enone 155. Iodide 153, on the other hand, can be traced retrosynthetically to the commercially available, optically active building block methyl (S)-(+)-3-hydroxy-2-methyIpropionate (154). 

A closer examination by ex situ analysis using NMR or gas chromatography illustrates that intrazeolite reaction mixtures can get complex. For example photooxygenation of 1-pentene leads to three major carbonyl products plus a mixture of saturated aldehydes (valeraldehyde, propionaldehyde, butyraldehyde, acetaldehyde)38 (Fig. 33). Ethyl vinyl ketone and 2-pentenal arise from addition of the hydroperoxy radical to the two different ends of the allylic radical (Fig. 33). The ketone, /i-3-penten-2-one, is formed by intrazeolite isomerization of 1-pentene followed by CT mediated photooxygenation of the 2-pentene isomer. Dioxetane cleavage, epoxide rearrangement, or presumably even Floch cleavage130,131 of the allylic hydroperoxides can lead to the mixture of saturated aldehydes. 

The vinyl silane 247 was unmasked to the ketone 250 by epoxidation, subsequent ring opening of the epoxide with HF in pyridine and concurrent cleavage of the THP and TBS protecting group (Scheme 39). The Stork-Jung annulation was completed through the treatment of the diketone 250 with sodium methoxide to mediate the intramolecular aldol con-... 

A series of functionalized alkenes has been subjected to selective epoxidation reactions. Oxidation of perfluorinated vinyl polyethers by bubbling oxygen through the liquid that contains a catalytic amount of a Lewis acid, e.g. antimony(V) fluoride, results in the formation of acid fluorides together with a smaller amount of C = C bond cleavage.76 Perfluorinated pentaaIkyI-2.3-dihydrofuran 38, an example of an unsaturated cyclic ether that is quite stable owing to perfluoroalkylation. is epoxidized by hypochlorite to the product 39 at 45 C.62... 

Cleavage of vinyl epoxides to cis-diols. In the presence of a Pd(0) catalyst, prepared by reaction of BuLi (2 equiv.) with Pd(OAc)2 (1 equiv.) and P(0-/-Pr)3 (excess) in THF, carbon dioxide reacts with vinyl epoxides to give carbonates of vinyl cw-l -diols.1... 

When perfluoro-2-methylpent-2-ene reacts with glycidol, the initially formed product is vinyl ether 38, whose epoxide ring opens under the action of mineral acids (8% HBr, 33% HC1). Alcohol 39 formed in the course of ring cleavage is readily cyclized into 1,3-dioxolane 40 in the presence of catalytic amounts of NEt3. 

Animals. The major metabolic routes are epoxidation of the vinyl group, followed by hydration of the intermediate epoxide, and by hydrolytic cleavage of the heterocyclic ring. Eliminated in approximately equal proportions in the urine and feces, with the principal metabolite being Af-(3,5-dichlorophenyl)-2-methyl-2,3, 4-trihydroxybutanamide... 

Therefore several reactions were subjected to various antibody catalyses, e. g., ester and enol ether cleavage, transesteiification, ketone reduction. Cope rearrangement, ring closure via epoxide opening, or Diels-Alder cycloaddition [74, 75]. An exceptional reaction is the antibody-catalyzed Robinson annulation of triketone 28 to the Wieland-Miescher ketone 29 on a preparative scale. Surprisingly, even the alkylation of diketone 27 with methyl vinyl ketone was catalyzed by the same antibody, but at moderate rates (Scheme 15) [76]. 

A study has been made of the kinetics of epoxidation of allylphosphinates and of the addition of C-benzoyl-iV-phenylnitrone to vinyl- and allyl-phosphonates. Boron trifluoride stabilizes phosphorus(v) thiocyanates, preventing their isomerization to isothiocyanates. Cleavage of the phosphinothioic methanesulphonic anhydride (97) with aluminium halides yields the phosphinic halide with retained chirality. ... 

Aminolysis of the azetidin-2-one (28) results, via epoxide opening, in cleavage of the amide bond to form the pyrrolidinone (29). The addition of A(-lithio-4-vinylazetidin-2-one to vinyl phosphonates allows ready access to the carbapenam ring-system. ... 

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