Oxyfunctionalized products

P450s belong to the class ofoxidoreductases and are classically described as heme b-containing monooxygenases that utilize the nicotinamide cofactors NADPH or NADH to reductively cleave atmospheric dioxygen to form an oxyfunctionalized product and a molecule ofwater. In many cases, the products represent hydroxylated derivatives of the substrate at one of its carbon moieties, as demonstrated in the generalized reaction mediated by these enzymes (Scheme 5.1). 

In an interesting paper by Bernini et al., compounds with a flavonoid structure have been selectively oxyfunctionalized at the C-2 carbon atom by dimethyldioxirane (DMD). Products obtained in this way appeared to be useful starting materials to access anthocyani-dins. An example of this route is presented in Scheme 10.1. Here, 2,4-cw-flavane-4-acetate (A) was oxidized by DMD at room temperature, affording the corresponding C-2 hydroxy derivative (B) as the only product (63% yield). Further treatment of B with silica gel eliminated acetic acid to give C quantitatively. Then C was easily transformed into the flavylium salt (D) by simple addition of a 37% solution of HCl in water. 

Oxyfunctionalization reactions of n-alkanes are carried out at room temperature and atmospheric pressure with t.BHP as oxidans and acetone as solvent. Product analysis was done with GC on a 50 m CP Sil-88 capillary column from Chrompack. 

In recent years, oxyfunctionalization of various natural products (steroids, alkaloids) under superacidic conditions have also been explored. In addition, Nafion resins in combination with various oxidizing agents have also been used in the oxygenations. 

This concept has been applied for the synthesis of the structurally complex and highly oxyfunctionalized triquinane (—)-coriolin (Sch. 31) [61]. Two carbonyl groups, both in the right position for 1,2-acyl shift were present in the trimethyl-functionalized bicyclo[2.2.2]octenone 58. With a site-selectivity of 85% the expected regioisomeric tricyclic dione 59 was formed as a mixture of epimers (Sch. 31). Subsequent transformations involving the annulations of the third five-membered ring as well as epoxidation and hydroxylation steps led to the desired natural product... 

Direct oxidation of benzene to phenol is of great interest not only for its industrial importance, but also from a purely scientific point of view. Apart from many earlier reports [35] on the oxidation of benzene to phenol by hydroxyl radicals generated by the reaction of Fe2+ salt (Fenton reagent) with H202 not much is known about the homogeneously catalysed oxyfunctionalization of aromatic C-H bonds. The lack of studies is largely attributable to the fact that the activation of the C-H bond in benzene is difficult owing to its resonance stability and the reactivity of phenol, which is consecutively oxidized to quinones and other by-products. 

Under similar conditions, the oxidation of m-xylene on the three Sn-silicalites shows similar conversions and H2O2 efficiencies, but the product distribution is different (Table 5). The products from the oxidation of the -CH3 group (3-methylbenOTl alcohol and aldehyde are the major components (about 70%) and the phenolic products (2,4-, 2,6-and 3,5-dimethylphenols) constitute 26% of the products after 24 h of reaction. Such a selectivity could result from the greater possibility of either of the two methyl groups undergoing oxyfunctionalization than the aromatic hydroxylation over Sn sites. 

The unusual reactivity of dioxiranes is impressively exhibited in their ability to insert into C — H bonds (Scheme 7) [28]. Thus, tertiary alkanes are oxidized to their respective alcohols [29]. In the example shown, the insertion took place with complete retention of configuration at the chirality center. 1,3-Dicarbonyl derivatives [30] are hydroxylated with high efficiency, but more than likely the intermediary enol is being oxyfunctionalized. Secondary alcohols are transformed into ketones, a specific example is the oxidation of the epoxy alcohol in the rosette [31], In an attempt to epoxidize the hydroxy acrylic ester [22], the epoxy 1,3-dicarbonyl product was obtained, although in low yield in accord with its rather reluctant nature towards oxidation. 

Although less effective than methyl(trifluoromethyl)dioxirane (TFDO), oxyfunctionalization of unactivated methine C-Hs with dimethyldioxirane (DDO) is feasible for various substituted steroids related to the 5/)-cholane and 5a-cholestane series to give novel mono- and dihydroxylated steroids. The reactivity and site selectivity of oxyfunctionalization is affected conspicuously by the structural and steric environments of the target methine carbon atoms. This nonenzymatic procedure may be advantageously applied to selective and short-course s)mtheses of bioactive steroids. Thus, the major reaction product of methyl... 

In the case of sp carbon center oxyfunctionalization with hydrogen peroxide in the presence of POMs, the possibility of autoxidation seems to be ruled out, since similar results were obtained under an argon atmosphere, in comparison with those achieved in the presence of air. Moreover, radical processes can be ruled out, as the presence of a radical scavenger in the reaction media did not inhibit the formation of any reaction products [52],... 

One of the most important selective oxidation processes in the production of chemicals is the side chain oxidation of alkyl aromatics, which are then further reacted to higher value products that end up in a variety of polymer compositions and specialised chemicals.The largest oxyfunctionalised aromatic products with regard to world production are terephthalic acid, phthalic anhydride and benzoic acid which are produced worldwide with capacities of >30,000, 5,000 and 500 kt a respectively. Worldwide production capacities for benzaldehyde and pyromel-litic dianhydride do not rise above 50 kt a In smaller capacities as specialty chemicals for the pharmaceutical industry, halo-substituted oxyfunctionalized aromatics are also produced. Of the aforementioned products, phthalic anhydride and pyromellitic dianhydride are produced from gas-phase processes using V20s-Ti02 catalysts and a liquid-phase alternative process does not appear immediately desirable. On the other hand, terephtalic and benzoic acids, and benzaldehyde are... 

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