Alkenes, oxidative

Although it is not a reaction of alkenes, oxidation of some alkanes with Pd(ll) is cited here. 1-Adamantyl Irilluoroacetate (155) was obtained in above 50% yield by the reaction of adamantane with Pd(OAc)2 in trifluoroa-cetic acid at 80 C[171]. 

Hydroboration-oxidation (Sections 6 11-6 13) This two step sequence achieves hydration of alkenes in a ste reospecific syn manner with a regiose lectivity opposite to Markovnikov s rule An organoborane is formed by electro philic addition of diborane to an alkene Oxidation of the organoborane inter mediate with hydrogen peroxide com pletes the process Rearrangements do not occur... 

Materials that typify thermoresponsive behavior are polyethylene—poly (ethylene glycol) copolymers that are used to functionalize the surfaces of polyethylene films (smart surfaces) (20). When the copolymer is immersed in water, the poly(ethylene glycol) functionaUties at the surfaces have solvation behavior similar to poly(ethylene glycol) itself. The abiUty to design a smart surface in these cases is based on the observed behavior of inverse temperature-dependent solubiUty of poly(alkene oxide)s in water. The behavior is used to produce surface-modified polymers that reversibly change their hydrophilicity and solvation with changes in temperatures. Similar behaviors have been observed as a function of changes in pH (21—24). 

Uses. Magnesium alkyls are used as polymerization catalysts for alpha-alkenes and dienes, such as the polymerization of ethylene (qv), and in combination with aluminum alkyls and the transition-metal haUdes (16—18). Magnesium alkyls have been used in conjunction with other compounds in the polymerization of alkene oxides, alkene sulfides, acrylonitrile (qv), and polar vinyl monomers (19—22). Magnesium alkyls can be used as a Hquid detergents (23). Also, magnesium alkyls have been used as fuel additives and for the suppression of soot in combustion of residual furnace oil (24). 

DJERASSI RYLANDER Oxidation Ru04 in oxidative cleavage ot phenols or alkenes oxidation ol aromatics to quinones oxidation ol alkyl amides to irmdes or ol ethers lo esters... 

In the same spirit DFT studies on peroxo-complexes in titanosilicalite-1 catalyst were performed [3]. This topic was selected since Ti-containing porous silicates exhibited excellent catalytic activities in the oxidation of various organic compounds in the presence of hydrogen peroxide under mild conditions. Catalytic reactions include epoxidation of alkenes, oxidation of alkanes, alcohols, amines, hydroxylation of aromatics, and ammoximation of ketones. The studies comprised detailed analysis of the activated adsorption of hydrogen peroxide with... 

Iron complexes with the pentadentate ligand 3 derived from pyridyl and prolinol building blocks containing a stereogenic center were reported from the group of Klein Gebbink (Scheme 4) [34]. In alkene oxidations with hydrogen peroxide,... 

Alkynes are reactive toward hydroboration reagents. The most useful procedures involve addition of a disubstituted borane to the alkyne, which avoids complications that occur with borane and lead to polymeric structures. Catechol borane is a particularly useful reagent for hydroboration of alkynes.212 Protonolysis of the adduct with acetic acid results in reduction of the alkyne to the corresponding cw-alkene. Oxidative workup with hydrogen peroxide gives ketones via enol intermediates. 

Ceria-based OSC compounds may have an impact on oxidation reactions especially when the catalysts are working around the stoichiometry (as this is the case under TW conditions). One of the first systematic studies was reported by Yu Yao [53,54], Most results were obtained in 02 excess (0.5% CO + O.5% 02 or 0.1% HC+ 1% 02). Several series of Pt, Pd and Rh/Al203 of various dispersion, as well as metal foils, were investigated in CO, alkane and alkene oxidation. The effect of metal dispersion in CO and the propane oxidation are shown in Figure 8.5. 

Recently, we have demonstrated another sort of homogeneous sonocatalysis in the sonochemical oxidation of alkenes by O2. Upon sonication of alkenes under O2 in the presence of Mo(C0) , 1-enols and epoxides are formed in one to one ratios. Radical trapping and kinetic studies suggest a mechanism involving initial allylic C-H bond cleavage (caused by the cavitational collapse), and subsequent well-known autoxidation and epoxidation steps. The following scheme is consistent with our observations. In the case of alkene isomerization, it is the catalyst which is being sonochemical activated. In the case of alkene oxidation, however, it is the substrate which is activated. 

Yasenkov, S. and Frei, H. (1998). Time-resolved FT-infrared spectroscopy of visible light-induced alkene oxidation by 02 in a zeolite. J. Phys. Chem. B 102, 8177-8182... 

Computational studies of alkene oxidation reactions by metal-oxo compounds, 38, 131 Computational studies on the mechanism of orotidine monophosphate decarboxylase,... 

Catalyst Alkene Oxidizing agent Stage 1 alkene to epoxide Stage 2 epoxide to cyclic carbonate ... 

Knops-Gerrits, P.-P., De Vos, D., Thibault-Starzyk, F. and Jacobs, P. A. Zeolite-encapsulated Mn(II) complexes as catalysts for alkene oxidation, Nature, 369 (1994), 543-546... 

On the other hand, in cyclic ethers (alkene oxides, oxetans, tetrahydrofuran) and formals the reaction site is a carbon-oxygen bond, the oxygen atom is the most basic point, and, hence, cationic polymerization is possible. The same considerations apply to the polymerization of lactones Cherdron, Ohse and Korte showed that with very pure monomers polyesters of high molecular weight could be obtained with various cationic catalysts and syncatalysts, and proposed a very reasonable mechanism involving acyl fission of the ring [89]. 

The reaction mechanisms of these transition metal mediated oxidations have been the subject of several computational studies, especially in the case of osmium tetraoxide [7-10], where the controversy about the mechanism of the oxidation reaction with olefins could not be solved experimentally [11-20]. Based on the early proposal of Sharpless [12], that metallaoxetanes should be involved in alkene oxidation reactions of metal-oxo compounds like Cr02Cl2, 0s04 and Mn04" the question arose whether the reaction proceeds via a concerted [3+2] route as originally proposed by Criegee [11] or via a stepwise [2+2] process with a metallaoxetane intermediate [12] (Figure 2). 

Alkene oxides, i.e., epoxides of C=C bonds, be they isolated or conjugated ... 

Diol epoxides, a very special and highly reactive subclass of alkene oxides encountered in the metabolism of polycyclic aromatic hydrocarbons. 

The overall reaction catalyzed by epoxide hydrolases is the addition of a H20 molecule to an epoxide. Alkene oxides, thus, yield diols (Fig. 10.5), whereas arene oxides yield dihydrodiols (cf. Fig. 10.8). In earlier studies, it had been postulated that epoxide hydrolases act by enhancing the nucleo-philicity of a H20 molecule and directing it to attack an epoxide, as pictured in Fig. 10.5, a [59] [60], Further evidence such as the lack of incorporation of 180 from H2180 into the substrate, the isolation of an ester intermediate, and the effects of group-selective reagents and carefully designed inhibitors led to a more-elaborate model [59][61 - 67]. As pictured in Fig. 10.5,b, nucleophilic attack of the substrate is mediated by a carboxylate group in the catalytic site to form an ester intermediate. In a second step, an activated H20... 

Together with glutathione conjugation, hydration is a major pathway in the inactivation and detoxification of arene oxides. Exceptions to this rule will be treated when discussing polycyclic aromatic hydrocarbons. Arene oxides are good substrates for microsomal EH, as evidenced in Table 10.1, where hydration of selected arene oxides, alkene oxides, and cy-cloalkene oxides by purified rat liver epoxide hydrolase is compared. The hy- ... 

As explained in the Introduction, alkene oxides (10.3) are generally chemically quite stable, indicating reduced reactivity compared to arene oxides. Under physiologically relevant conditions, they have little capacity to undergo rearrangement reactions, one exception being the acid-catalyzed 1,2-shift of a proton observed in some olefin epoxides (see Sect. 10.2.1 and Fig. 10.3). Alkene oxides are also resistant to uncatalyzed hydration, thus, in the absence of hydrolases enzymes, many alkene oxides that are formed as metabolites are stable enough to be isolated. 

The data in Table 10.1 suggest that the reactivity of epoxide hydrolase toward alkene oxides is highly variable and appears to depend, among other things, on the size of the substrate (compare epoxybutane to epoxyoctane), steric features (compare epoxyoctane to cycloalkene oxides), and electronic factors (see the chlorinated epoxides). In fact, comprehensive structure-metabolism relationships have not been reported for substrates of EH, in contrast to some narrow relationships that are valid for closely related series of substrates. A group of arene oxides, along with two alkene oxides to be discussed below (epoxyoctane and styrene oxide), are compared as substrates of human liver EH in Table 10.2 [119]. Clearly, the two alkene oxides are among the better substrates for the human enzyme, as they are for the rat enzyme (Table 10.1). 

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