Oxidation alkene epoxidation

They include aromatic hydroxylation, hydrocarbon and alcohol oxidation, alkene epoxidation, nitro-aromatic reduction, dehydrogenation, carbonylation, cyclization, heterocycle functionalization, etc. 

Key Words Direct propylene epoxidation. Propylene oxide, Gold, Titanium, Propene, Au/Ti catalysts. Catalysis by gold. Titanium silicalite, TS-1, Gold/TS-1, Hydrogen peroxide, Kinetics, Design of experiments, Deposition-precipitation, Ammonium nitrate, Selective oxidation, Alkene epoxidation, Density functional theory, DFT calculations, QM/MM calculations. 2008 Elsevier B.v. 

In general, peroxomonosulfates have fewer uses in organic chemistry than peroxodisulfates. However, the triple salt is used for oxidizing ketones (qv) to dioxiranes (7) (71,72), which in turn are useful oxidants in organic chemistry. Acetone in water is oxidized by triple salt to dimethyldioxirane, which in turn oxidizes alkenes to epoxides, polycycHc aromatic hydrocarbons to oxides and diones, amines to nitro compounds, sulfides to sulfoxides, phosphines to phosphine oxides, and alkanes to alcohols or carbonyl compounds. 

Compounds lb and 2b were the Urst fluorinated ligands tested in Mn-catalyzed alkene epoxidation [5,6]. The biphasic Uquid system perfluorooc-tane/dichloromethane led to excellent activity and enantioselectivity (90% ee) in the epoxidation of indene with oxygen and pivalaldehyde (Scheme 1, Table 1). In addition, the fluorous solution of the catalyst was reused once and showed the same activity and selectivity. This represents a considerable improvement over the behavior in the homogeneous phase, where the used catalyst was bleached and reuse was impossible. Unfortunately, indene was the only suitable substrate for this system, which failed to epoxidize other alkenes (such as styrene or 1,2-dihydronaphthalene) with high enantioselectivity. The system was also strongly dependent on the oxidant and only 71% ee was obtained in the epoxidation of indene with mCPBA at - 50 °C. 

The scope of reactions involving hydrogen peroxide and PTC is large, and some idea of the versatility can be found from Table 4.2. A relatively new combined oxidation/phase transfer catalyst for alkene epoxidation is based on MeRe03 in conjunction with 4-substituted pyridines (e.g. 4-methoxy pyridine), the resulting complex accomplishing both catalytic roles. 

Finally, with the aim of discovering novel chiral oxomolybdenum catalysts able to perform enantioselective alkene epoxidations, Kuhn et al. have reported the exploration of the catalytic behaviour of a series of dioxomolybdenum(VI) complexes with chiral cw-8-phenylthiomenthol ligands derived from ( + )-pulegone. Therefore, the epoxidation of c -p-methylstyrene using t-butyl-hydroperoxide as the oxidant and performed in the presence of ( + )-(2i ,5i )-2-[1-methyl-l-(phenylthio)ethyl]-5-methylcyclohexanone oxime as the ligand, did not produce, however, a significant optical induction in these conditions. 

Alkenes may be oxidized to epoxides that are reactive metabolites because of ring strain [36] and can undergo nucleophilic attack. Epoxides are not always highly reactive species. In fact, some of them are relatively unreactive for example, the arene oxides that derive from oxidation of phenyl rings. Most drugs containing a phenyl... 

Furans and thiophenes are believed to be oxidized to epoxides, following the general reaction described for alkenes. However, at least in the case of tienilic add, experimental evidence shows that the reactive intermediate is an S-oxide [39]. Another example of CYP inactivation by a thiophene derivative is the covalent binding of ticlopidine to CYP2C19 [40]. 

In contrast, a number of alkene epoxides (10.3) are chemically quite stable, i.e., intrinsically less reactive than arene oxides. Examples of epoxide metabolites that have proven to be stable enough to be isolated in the absence of degrading enzymes include 1,2-epoxyoctane (10.4), 1,2-epoxycyclohex-ane (10.5), 1-phenyl-1,2-epoxy ethane (styrene oxide, 10.6), and cis- 1,2-diphenyl-1,2-epoxyethane (cfv-stilbene oxide, 10.7) [12], The same is true of alclofenac epoxide (10.8), hexobarbital epoxide (10.9), and a few other epoxides of bioactive compounds. 

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- ... 

In addition to the unfunctionalized alkene epoxides discussed in the previous subsection, various other types of epoxides exist that are also derived from unconjugated alkenes but that share two additional features, i. e., being characterized by the presence of one or more functional group(s) and having biological significance. Thus, the present subsection examines epoxy alcohols, epoxy fatty acids, allylbenzenes 2, 3 -oxides, as well as alkene oxide metabolites of a few selected drugs. 

S.3 Cytochrome P450 Model Compounds Functional. Ferric-peroxo species are part of the cytochrome P450 catalytic cycle as discussed previously in Section 7.4.4. For instance, these ferric-peroxo moieties are known to act as nucleophiles attacking aldehydic carbon atoms in oxidative deformylations to produce aromatic species.An example of this work, establishing the nucleophilic nature of [(porphyrin)Fe (02)] complexes, was achieved for alkene epoxidation reactions by J. S. Valentine and co-workers. The electron-deficient compound menadione (see Figure 7.18) yielded menadione epoxide when reacted with a [(porphyrin)Fe X02)] complex. 

Other examples of oxidant-iron(III) adducts as intermediates in iron porphyrin-catalyzed reactions have been published as listed in references 54a-k. Competitive alkene epoxidation experiments catalyzed by iron porphyrins with peroxy acids, RC(0)00F1, or idosylarenes as oxidants have been proposed to have various intermediates such as [(porphyrin)Fe (0-0-C(0)R] or [(porphyrin)Fe (0-I-Ar)]. Alkane hydroxylation experiments catalyzed by iron porphyrins with oxidant 3-chloroperoxybenzoic acid, m-CPBA, have been proposed to operate through the [(porphyrin)Fe (0-0-C(0)R] intermediate. J. P. CoUman and co-workers postulated multiple oxidizing species, [(TPFPP )Fe =0] and/or [(TPFPP)Fe (0-I-Ar)] in alkane hydroxylations carried out with various iodosylarenes in the presence of Fe(TPFPP)Cl, where TPFPP is the dianion of me50-tetrakis(pentafluorophenyl)porphyrin. ... 

The kinetics of the catalytic oxidation of cyclopentene to glutaraldehyde by aqueous hydrogen peroxide and tungstic acid have been studied and a compatible mechanism was proposed, which proceeds via cyclopentene oxide and /3-hydroxycyclopentenyl hydroperoxide. " Monosubstituted heteropolytungstate-catalysed oxidation of alkenes by t-butyl hydroperoxide, iodosobenzene, and dioxygen have been studied a radical mechanism was proved for the reaction of alkenes with t-BuOOH and O2, but alkene epoxidation by iodosobenzene proceeds via oxidant coordination to the catalyst and has a heterolytic mechanism. ... 

A chiral dichlororuthenium(IV) complex of a Z)4-symmetric porphyrin, [Ru (Z)4-por )(Cl)2], has been prepared by heating [Ru (Z>4-por )(CO)(MeOH)] in CCI4. The complex is characterized by NMR (paramagnetically shifted pyrrolic protons at = 52.3 ppm), FAB-MS, and magnetic susceptibility measurement (/.teff= 3.1/.tB). It is a very active catalyst for enantioselective alkene epoxidations using 2,6-dichloropyridine A-oxide as the terminal oxidant, with a turnover number of up to 2000 the ee of the epoxides is 50-80%. The complex can be incorporated into sol-gel and turnovers of over 10" can be achieved." ... 

While it is well established that HO—ONO can be involved in such two-electron processes as alkene epoxidation and the oxidation of amines, sulfides and phosphines, the controversy remains concerning the mechanism of HO-ONO oxidation of saturated hydrocarbons. Rank and coworkers advanced the hypothesis that the reactive species in hydrocarbon oxidations by peroxynitrous acid, and in lipid peroxidation in the presence of air, is the discrete hydroxyl radical formed in the homolysis of HO—ONO. The HO—ONO oxidation of methane (equation 7) on the restricted surface with the B3LYP and QCISD methods gave about the same activation energy (31 3 kcalmol" ) irrespective of basis set size . ... 

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