Alkenes mild oxidation

This catalyst can catalyze a new reaction, called alkane metathesis. By this reaction, alkanes are transformed into higher and lower alkanes.265 Silica-supported zirconium catalysts were also used for the mild oxidation of alkenes by H202 266... 

The oxidation of organic substances by cyclic peroxides has been intensively studied over the last decades , from both the synthetic and mechanistic points of view. The earliest mechanistic studies have been carried out with cyclic peroxides such as phthaloyl peroxide , and more recently with a-methylene S-peroxy lactones and 1,2-dioxetanes . During the last 20 years, the dioxiranes (remarkable three-membered-ring cyclic peroxides) have acquired invaluable importance as powerful and mild oxidants, especially the epoxidation of electron-rich as well as electron-poor alkenes, heteroatom oxidation and CH insertions into alkanes (cf. the chapter by Adam and Zhao in this volume). The broad scope and general applicability of dioxiranes has rendered them as indispensable oxidizing agents in synthetic chemistry this is amply manifested by their intensive use, most prominently in the oxyfunctionalization of olefinic substrates. 

These multicomponent catalyst systems have been employed in a variety of aerobic oxidation reactions [27]. For example, use of the Co(salophen) cocatalyst, 1, enables selective allylic acetoxylation of cyclic alkenes (Eq. 6). Cyclo-hexadiene undergoes diacetoxylation under mild conditions with Co(TPP), 2 (Eq. 7), and terminal alkenes are oxidized to the corresponding methyl ketones with Fe(Pc), 3, as the cocatalyst (Eq. 8). 

Notes A useful and relatively mild oxidizing agent. Most current use attempts to use catalytic amounts.of OsCh thus NMO is used as a co-oxidant with OSO4 for hydroxylation of alkenes. A method has been developed that allows catalytic amounts of NMM (A-methylmorpholine) to be used.1... 

Iodosobenzene bistrifluoroacetate is a versatile mild oxidant that has been used to oxidize a broad range of organic compounds, such as alkenes, alkynes, carbonyl compounds, and alcohols Its application in organic synthesis has been summarized m several recent reviews devoted to polyvalent iodine compounds [63, 64, 65]... 

Gold NPs deposited on carbons are active and selective for mild oxidations in liquid phase although they exhibit almost no catalytic activity in the gas phase. Examples are aerobic oxidation of mono-alcohols, diols, glycerol, glucose, alkenes and alkanes. 

Tandem radical addition/cydization reactions have been performed using unsaturated tertiary amines (Scheme 9.11) [14,15]. Radical attack is highly stereoselective anti with respect to the 5-alkoxy substituent of 2-(5f-J)-furanones, which act as the electron-deficient alkenes. However, the configuration of the a position of the nitrogen cannot be controlled. Likewise, tandem addition cyclization reactions occur with aromatic tertiary amines (Scheme 9.12) in this case, acetone (mild oxidant) must be added to prevent the partial reduction of the unsaturated ketone [14]. 

Reductive decomplexation/ Although the common practice for removal of the hexacarbonyldicobalt residue from alkyne complexes involves mild oxidants, it is also possible to convert the complexes to free (Z)-alkenes with BUjSnH. If triethylsilane is used the decomplexation is followed by in situ hydrosilylation. 

Building upon this promising chemistry, Stoltz and coworkers [50] extended the scope of the mild oxidation system to the formation of other cyclic compounds - specifically, benzo-furans and dihydrobenzofurans. Aryl allyl ether 142 was subjected to the Pd(OAc)2/ethyl nicotinate catalyst under a variety of oxidants to provide benzofuran 144. Presumably, this reaction proceeds by initial palladation, followed by alkene insertion and )3-hydride elimination to form vinylic intermediate 143, which then isomerizes to the more thermodynamically stable benzofuran 144. Although molecular oxygen was a suitable oxidant for this reaction (Table 9.2 entry 1), benzoquinone appeared to be the optimal reoxidant (Table 9.2 entry 2), providing the highest overall yields. 

Further attempts to increase the kinetics and biocompatibility of 1,3-dipolar cycloadditions led organic chemists to explore altemative dipoles that react with multiple-bond reaction partners. Nitrile oxides are highly reactive dipoles that can react with various alkenes and alkynes to provide isoxazolines and isoxazoles, respectively. In the absence of a suitable reacting partner, nitrile oxides tend to dimerize to form fiiroxane derivatives, or can alternatively act as electrophiles. However, when generated in situ from suitable precursors such as hydroximoyl chlorides or by mild oxidation directly from oximes, nitrile oxides were successfully applied to the labeling of nucleic acids [43], peptides [44] and carbohydrates [45] (Fig. 7). 

The peroxy intermediate (1) is an excellent reagent for the synthesis of acid-sensitive benzylic epoxides from alkenes, the oxidation of benzylic CH2 to C=0, and the chemoselective oxidation of alkene sulfoxides to alkene sulfones. It is noteworthy that the reactions are carried out under mild conditions (—35 °C). 

The oxidized electron transfer mediator (ETMox). namely the peroxo complexes of methyltrioxorhenium (MTO) and vanadyl acetylacetonate [VO(acac)2] and flavin hydroperoxide, generated from its reduced form (Figure 1.1) and H2O2, recycles the N-methylmorpholine (NMM) to N-methylmorpholine N-oxide (NMO), which in turn reoxidizes the Os(VI) to Os(VIII). While the use of hydrogen peroxide as oxidant without any electron transfer mediators is inefficient and nonselective, various alkenes were oxidized to diols in good to excellent yields employing this mild triple catalytic system (Scheme 1.2). 

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