Alkenes oxidative functionalization chemistry

The availability of 18 in one synthetic step via direct oxidative functionalization of HCTD [19-21] allows exploration of this valuable compound s chemistry, for the first time. Thus, the reaction sequence shown in Scheme 9 has been utilized to prepare a novel polycyclic alkene, 30, whose s unmetry properties require that its central, tetrasubstituted C=C double bond be completely planar (in the isolated molecule). The constraints imposed by the polycarbocyclic cage framework cause the CCC bond angles about the central C=C double bond in 30 to deviate significantly from the preferred value of 120°, thereby introducing additional steric strain in this molecule beyond that which is associated with its framework alone. 

Nearly everything my group has done in polymer-facilitated catalysis uses soluble polymers, a practice that has been followed by others as well.(5-7) Our group has emphasized chemistry using soluble polymers where the polymers are separable by some sort of precipitation or phase isolation technique. This paper presents examples of several catalysts and discusses several sorts of polymers. First, there is a discussion of some of our older work using functionalized polyolefins as the support. In this case, catalyst use, recovery and separation are possible because polyethylene is insoluble in all solvents at room temperature but soluble on heating. Next, the paper discusses catalysts that separate on heating. Two examples, poly(alkene oxide)-supported catalysts and poly(N-isopropylacrylamide)-supported catalysts that both... 

Oxidation is the first step for producing molecules with a very wide range of functional groups because oxygenated compounds are precursors to many other products. For example, alcohols may be converted to ethers, esters, alkenes, and, via nucleophilic substitution, to halogenated or amine products. Ketones and aldehydes may be used in condensation reactions to form new C-C double bonds, epoxides may be ring opened to form diols and polymers, and, finally, carboxylic acids are routinely converted to esters, amides, acid chlorides and acid anhydrides. Oxidation reactions are some of the largest scale industrial processes in synthetic chemistry, and the production of alcohols, ketones, aldehydes, epoxides and carboxylic acids is performed on a mammoth scale. For example, world production of ethylene oxide is estimated at 58 million tonnes, 2 million tonnes of adipic acid are made, mainly as a precursor in the synthesis of nylons, and 8 million tonnes of terephthalic acid are produced each year, mainly for the production of polyethylene terephthalate) [1]. 

Oxidations of various organic functional groups such as alcohols or alkenes are some of the most important transformations in organic chemistry. Unfortunately, their use is sometimes restricted hy poor selectivities or the need for transition metals and other species, which might be toxic or difficult to remove during work-up. Therefore, numerous attempts have been made to immobihze oxidants on a solid support [4], and these are compiled in the following. 

The synthetically most valuable intermediate in heterofullerene chemistry so far has been the aza[60]fulleronium ion C59N (28). It can be generated in situ by the thermally induced homolytic cleavage of 2 and subsequent oxidation, for example, with O2 or chloranil [20-24]. The reaction intermediate 28 can subsequently be trapped with various nucleophiles such as electron-rich aromatics, enolizable carbonyl compounds, alkenes and alcohols to form functionalized heterofullerenes 29 (Scheme 12.8). Treatment of 2 with electron-rich aromatics as nucleophilic reagent NuH in the presence of air and excess of p-TsOH leads to arylated aza[60]fullerene derivatives 30 in yields up to 90% (Scheme 12.9). A large variety of arylated derivatives 30 have been synthesized, including those containing cor-annulene, coronene and pyrene addends [20, 22-25]. 

As soon as, it was learnt that oxoammonium salts, which are unstable compounds, are very efficient in the oxidation of alcohols, and that they can be generated in situ by treating catalytic TEMPO, or related compounds, with MCPBA acting as a secondary oxidant, it became apparent that other secondary oxidants would be more practical than MCPBA in Synthetic Organic Chemistry. MCPBA is a very energetic oxidant that reacts with many functionalities including alkenes and ketones. 

The reactions of hydrogen peroxide with vanadate have been of interest for many years. Much of the early work was concerned with the function of peroxovanadates as oxygen transfer agents. Alkenes and similar compounds such as allyl alcohols can be hydroxylated or epoxidized. Even alkanes can be hydroxylated, whereas alcohols can be oxidized to aldehydes or ketones and thiols oxidized to sulphones or sulphoxides. Aromatic molecules, including benzene, can be hydroxylated. The rich chemistry associated with the peroxovanadates has, therefore, led to extensive studies of their reaction chemistry. To this end, x-ray diffraction studies have successfully provided details of a number of peroxovanadate structures. 

Osmium-catalysed dihydroxylation of olefins is a powerful route towards enantioselective introduction of chiral centers into organic substrates [82]. Its importance is remarkable because of its common use in organic and natural product synthesis, due to its ability to introduce two vicinal functional groups into hydrocarbons with no functional groups [83]. Prof. Sharpless received the 2001 Nobel Prize in chemistry for his development of asymmetric catalytic oxidation reactions of alkenes, including his outstanding achievements in the osmium asymmetric dihydroxylation of olefins. 

Stoichiometric and catalytic transition-metal oxidation reactions are of great interest, because of their important role in industrial and synthetic processes. The oxidation of alkenes is one of the fundamental reactions in chemistry.1 Most bulk organic products contain functional groups, which are produced in the chemical industry by direct oxidation of the hydrocarbon feedstock. Usually these reactions employ catalysts to improve the yields, to reduce the necessary activation energy and render the reaction more economic. The synthesis of almost every product in chemical industry nowadays employs at least one catalytic step. The oxidation products of alkenes, epoxides and glycols, may be transformed into a variety of functional groups and therefore the selective and catalytic oxidation of alkenes is an industrially important process. 

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