Selenium dioxide oxidation ketones

Phenylsulfonyl)indole 330 was converted to a ketone by a set of standard reactions followed by the selenium dioxide oxidation of the resulting acetyl goup to the ketoaldehyde 332 (Scheme 101). Methylthiosemicarbazide hydroiodide reacted with 332 to the triazine 333 in 83% yield. As Diels-Alder reactions with 1 -pyrrolidinocyclohexene failed, 333 was first oxidized... 

An alternative practical synthesis of triquinacene-2-carboxylic acid (as the dextrorotatory enantiomer) has l n described by Deslongchamps and Soucy Their protocol begins with hydroxy ketone 467 and passes via the 2-methyl derivative (Scheme XXXVIII). Selenium dioxide oxidation of the hydrocarbon provided the aldehyde which was further oxidized and then hydrolyzed to arrive at the add. 

Selenium dioxide oxidation of the ketones (166 R = H, Cl) is reported115 to give the corresponding indolones (168) in moderate yield... 

The further progress of the synthesis involves the closing of ring VI. This was found to be very difficult to achieve, quite contrary, one supposes, to anticipation. All the obvious methods failed, and the successful method turned out to involve conversion of the acid CCXXX into the methyl ketone CCXXXI by pyridine and acetic anhydride, and selenium dioxide oxidation of this ketone to dehydrostrychninone (CCXXXII). 

Selenium-mediated allylic oxidations producing allylic alcohols have been discussed above however, in some cases oxidation proceeds further to give the a, -unsaturated carbonyl compounds directly, or mixtures of alcoholic and ketonic products. That the regioselectivity observed in these allylic oxidation reactions closely resembles that found in classical selenium dioxide oxidations is in accord with initial formation of the intermediate allylic alcohol before in situ oxidation to the carbonyl compound. This process was studied by Rapoport and was explained mechanistically as an elimination of the intermediate allylic selenite ester via a cyclic transition state, analogous to Ssi (rather than 5n20 solvolysis (Scheme 21). Of the two possible transition states (78) and (79), the cyclic alternative (78) was preferred tecause oxidation exclusively yields trans aldehydes. 

The preparation of certain substituted benzils by treatment of aryl benzyl ketones with selenium dioxide is discussed later (method 183). If a methyl ketone is treated under these conditions, the methyl group is oxidized to an aldehyde group/ The reaction is carried out by refluxing a mixture of selenium dioxide and ketone in dioxane or alcohol for several hours. Preparative details are found in the procedures for phenylglyoxal (72%) and glyoxal (74%) the latter is isolated as its bisulfite derivative. 

Most usual oxidizing agents act normally with imidazole aldehydes and ketones but l-benzylimidazole-2-carbaldehyde is reportedly somewhat resistant to selenium dioxide oxidation. Reduction of ketone functions under Clemmensen and Wolfi-Kischner conditions is usually successful. Zinc dust and acetic acid reduce acetyl groups to a mixture of secondary alcohol and ethyl borohydride gives the alcohol exclusively (B-76MI40701). 

Thiazolecarboxylic Acids, Thiazolecarboxaldehydes. and Thiazolyl Ketones 2. Selenium dioxide oxidation of carbinols (Scheme 29). 

In chemical oxidation or reduction the redox reagent and the substrate often form a covalent or ionic bond, for example, an ester in chromic acid oxidation [8], a sulfonium methylide in the Swern oxidation [9], cyclic esters in the svn dihydroxylation with OSO4 [10], or in the selenium dioxide oxidation of ketones and aldehydes [11]. In electrochemical processes the substrate must diffuse from the bulk of the solution to the electrode and compete there with other components of the electrolyte by competitive adsorption for a position at the electrode surface [12]. The next step is then generation of the reactive intermediate by electron transfer at the electrode that reacts with a low activation energy to the products. In chemical oxidations or reductions one finds a reductive or oxidative elimination of the intermediate with a higher activation energy. 

Selenium dioxide oxidation of ketones and aldehydes (Riley, 1932) O... 

Sharpless, K. B., Gordon, K. M. Selenium dioxide oxidation of ketones and aldehydes. Evidence for the intermediacy of P-ketoseleninic. J. 

Amax 263 mfjL. In accord with the assigned structure there was no resonance for a vinyl proton in the NMR spectrum. Selenium dioxide oxidation of 69 gave the conjugated ketone 74, v ax I , nd 1628 cm . The single vinyl proton in the NMR spectrum of this compound appeared at S 6.02. Catalytic reduction of 74 to 70 proved that rearrangement had not occurred in this series of reactions. 

Selenium dioxide oxidation of aryl ketone semicarbazones (4) in acetic acid affords 1,2,3-selenadiazoles (5). Pyrolysis of the latter gives selenium and the arylacetylenes (6) in good yield. The same procedure has been used to prepare cyclo-octyne in 34% yield. ... 

A selenium dioxide oxidation of activated methylenes into ketones. 

Selenium dioxide can be used to oxidize ketones and aldehydes to a-dicarbonyl compounds. The reaction often gives high yields of products when there is a single type of CH2 group adjacent to the carbonyl group. In unsymmetrical ketones, oxidation usually occurs at the CH2 that is most readily enolized.255... 

The oxidation is regarded as taking place by an electrophilic attack of selenium dioxide (or selenous acid, H2Se03, the hydrate) on the enol of the ketone or aldehyde. This is followed by hydrolytic elimination of the selenium.258... 

A mixture of 1,4-dioxane and water is often used as the solvent for the conversion of aldehydes and ketones by H2Se03 to a-dicarbonyl compounds in one step (Eq. 8.117).331 Dehydrogenation of carbonyl compounds with selenium dioxide generates the a, (i-unsaturated carbonyl compounds in aqueous acetic acid.332 Using water as the reaction medium, ketones can be transformed into a-iodo ketones upon treatment with sodium iodide, hydrogen peroxide, and an acid.333 Interestingly, a-iodo ketones can be also obtained from secondary alcohol through a metal-free tandem oxidation-iodination approach. 

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