Sequential oxidation

For example, Piers and Marais demonstrated that keto iodo alkene 32 can be converted to bicyclic keto alkene 35 in one pot21 (see Scheme 7). In this interesting methylenecyclopentane annulation method, it is presumed that intermediate 33, produced by sequential oxidative addition and deprotonation reactions, undergoes conver-... 

In the anaerobic photoheteio iophRhodobacter(Rhodopseudomonas) spheroides, a molybdenum enzyme in which the metal is coordinated by two equivalents of a pyranopterin cofactor is involved in sequential oxidations and reductions involving Mo(VI), Mo(V), and Mo(IV) (Cobb et al. 2005). 

Castro CE, DM Riebeth, NO Belser (1992a) Biodehalogenation the metabolism of vinyl chloride by Methylosinus trichosporium OB-3b. A sequential oxidative andreductive pathway through chloroethylene oxide. Environ Toxicol Chem 11 749-755. 

Chemical Oxidation—Processes in which contaminants are sequentially oxidized to less toxic products through the introduction of chemical oxidants79 or the creation of oxidizing conditions through other means, such as using UV radiation, electrical stimulation, or cavitation. 

Figure 7.35 Stereoinversion of 2-hydroxy acids using sequential oxidation and reduction...

The catalytic cycle of laccase includes several one-electron transfers between a suitable substrate and the copper atoms, with the concomitant reduction of an oxygen molecule to water during the sequential oxidation of four substrate molecules [66]. With this mechanism, laccases generate phenoxy radicals that undergo non-enzymatic reactions [65]. Multiple reactions lead finally to polymerization, alkyl-aryl cleavage, quinone formation, C> -oxidation or demethoxylation of the phenolic reductant [67]. 

Among the metal complexes used in electrocatalytic oxidation of organic compounds, polypyridyl oxo-ruthenium complexes have attracted special attention,494"508 especially [RuIV(terpy)(bpy)0]2+.495 197,499,500,502,504 This high oxidation state is reached from the corresponding Run-aqua complex by sequential oxidation and proton loss (Equations (75) and (76)). 

Since the substituted hydroquinones and quinone dioximes are better electron donors than hexamethylbenzene (as established by cyclic voltammetric studies), donor-induced disproportionation (to generate NO+ NOf) is even more favored. Furthermore, either two successive one-electron oxidations of hydro-quinone (or quinone dioxime) by NO + followed by the loss of two protons from the dication or two sequential oxidation/deprotonation steps complete the oxidative transformation in equation (97). Importantly, the ready aerial oxidation of NO to NO provides the basis for the nitrogen oxide catalysis of hydroquinone (or quinone dioxime) autoxidation as summarized in Scheme 26. 

FIGURE 1 7-3 Adenosine metabolites. Adenosine is converted to inosine by adenosine deaminase. Removal of the ribose by nucleoside phos phorylase produces hypoxanthine, which is sequentially oxidized to xanthine and uric acid by xanthine oxidase. 

The isomerization of allylic alcohols provides an enol (or enolate) intermediate, which tautomerizes to afford the saturated carbonyl compound (Equation (8)). The isomerization of allylic alcohols to saturated carbonyl compounds is a useful synthetic process with high atom economy, which eliminates conventional two-step sequential oxidation and reduction.25,26 A catalytic one-step transformation, which is equivalent to an internal reduction/oxidation process, is a conceptually attractive strategy due to easy access to allylic alcohols.27-29 A variety of transition metal complexes have been employed for the isomerization of allylic alcohols, as shown below. 

Nitrification is the sequential oxidation of NH4 to N02 and NO3 which proceeds according to the following reaction sequence ... 

As illustrated in Figure 19, which refers to [Co(triphos)(DBcat)]+, these complexes display both two sequential reduction processes centred on the metal ion and two sequential oxidation processes centred on the catechol ligand. 

Next step is the construction of 8- and 15-membered ring systems by sequential RCM [7]. Tetracyclic alcohol 13 was converted to 14 by sequential oxidation and Peterson olefination followed by deprotection of the TMS group. After protection of the amine with a Boc group, the imide carbonyl group was... 

Epimerization of carbohydrate stractures to the corresponding epi-hydroxy stereoisomers is an efficient means to generate compounds with inverse coirfiguration that may otherwise be cumbersome to prepare. Several different synthetic methods have been developed, including protocols based on the Mitsunobu reaction,sequential oxidation/reduction... 

Medici et al. have used a combined sequential oxidation-reduction to access a range of imsaturated secondary alcohols from their racemates [7] (Scheme 1). Here the S-alcohol 2 is oxidized by B. stereothermophilus which is displaying Prelog specificity leaving the l -enantiomer untouched. The other microorganism, Y. lipolytica contains an anti-Prelog dehydrogenase which is therefore able to reduce the ketone 1 to the l -alcohol 2. Thus the combination of the two steps effects a net deracemization of substrate 2. 

The preparation of the requisite y-keto-p-toluenesulfonate rac-35 as homo-Favorskii precursor commenced with commercially available 2,5-dihy-droanisole (36) that was protected and epoxidized to acetal rac-31 (Scheme 11). Regioselective opening of the epoxide with p-chlorophenylse-lenide followed by sequential oxidation to the selenoxide and thermal elimination generated an allylic alcohol that was protected to give pivaloate rac-38. 

VAM can be produced starting from ethylene, which is converted to acetic acid via acetaldehyde by two sequential oxidation steps (reactions 1 and 2 in Fig. 2), the first step being the famous Wacker process (reaction 1 in Fig. 2) [14]. 

Results obtained in glass apparatus are summarized in Figure 1. The unsaturation falls off nearly linearly after a short induction period. After the hydroperoxide functional groups attain their maximum, the olefin disappearance decreases and becomes nonlinear as it is consumed by reaction to form polymeric dialkyl peroxide functions. The maximum concentration of polymeric dialkyl peroxide occurs well after the maximum alkenyl hydroperoxide concentration, giving the appearance of a sequential oxidation mechanism. Infrared and gas-liquid chromatographic analyses showed that hydroxylic derivatives, carbonyl derivatives, and lower molecular weight olefins continued to build up as by-products as the oxidation proceeded, as does the acidity titer. 

Sequential Oxidation Products from Tropospheric Isoprene Chemistry MACR and MPAN at a NOt-Rich Forest Environment in the Southeastern United States, J. Geophys. Res., 103, 22463-22471 (1998). 

Nouaime, G S. B. Bertman, C. Seaver, D. Elyea, H. Huang, P. B. Shepson, T. K. Starn, D. D. Riemer, R. G. Zika, and K. Olszyna, Sequential Oxidation Products from Tropospheric Isoprene Chemistry MACR and MPAN at a NO,-Rich Forest Environment in the Southeastern United States, J. Geophys. Res., 103, 22463-22471 (1998). 

Nitrenium ions can be viewed as products from two-electron oxidation of amines (Fig. 13.13) followed by loss of a proton. Thus they need to be considered as intermediates in the oxidation of amines. In two early studies, diarylnitrenium ions were shown to have formed in the oxidation of diarylamines. Svanholm and Parker carried out cyclic voltammetry on A,A-di-(2,4-methoxyphenyl)amine (25) in acetonitrile with alumina added to suppress any adventitious nucleophiles. The voltam-mogram revealed two sequential oxidation processes (1) formation of the cation radical 26, and (2) either the nitrenium ion 27 or its conjugate acid. In strongly acidic solution the latter was sufficiently stable that its absorption spectrum could be recorded. 

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