Ketones by selenium dioxide

Many 1,2,3-selenadiazoles have been prepared as intermediates for the ultimate preparation of other organic compounds or for biological activity evaluation [6], The most general, extensively applied method is based on the oxidation of semicar-bazones, mostly derived from aromatic and carbocyclic ketones, by selenium dioxide [6, 14, 188-191], Synthesis of 4-(2-naphthyl)-l,2,3-selenazole (117) from semicarbazone (116) is an example (Scheme 36). 

Pati, S. C., Mishra, M. M. Kinetics and mechanism of the oxidation of aryl aliphatic ketones by selenium dioxide. Indian Journal of Physical... 

The oxidation of an aryl methyl ketone, with selenium dioxide [Method (a)] in a suitable solvent, to an aryl 1,2-ketoaldehyde is illustrated by the preparation... 

Methyl selenien-2-yl glyoxal,118 the simplest a-diketone of the selenophene series, has been obtained in two ways by oxidation of 2-propionylselenophene by selenium dioxide and by hydrolysis of the product resulting from nitrosation of that ketone. Its UV spectrum has three characteristic maxima (Amax 277, 283, and 310 mp). When... 

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. 

The methylene group adjacent to a ketone may be oxidized by selenium dioxide to give 1,2-dicarbonyl compounds. It is important to carry out base-catalysed condensations of ketones wherever possible under an atmosphere of nitrogen. The reason is that enolate anions are readily autoxidized by the oxygen in air to form hydroperoxides These may then undergo further reaction including decomposition to form diketones. 

During the enantioselective total synthesis of miroestrol by E.J. Corey and co-workers, the introduction of a hydroxyl group was required at one of the bridgehead positions. This position was a to a ketone and was also the allylic position to a double bond. The oxidation was effected by selenium dioxide/fert-butyl hydroperoxide at 25 °C. 

The conversion of 187 into lycopodine was readily accomplished. Reduction of 187 with lithium aluminum hydride gave the mixture of epimeric alcohols 193 that was oxidized with Jones reagent to the ketone 192. Selenium dioxide gave the known diosphenol 194 which was converted into a separable mixture of lycopodine, anhydro-dihydrolycopodine (195), and dihydrodeoxylycopodine (196) by heating with hydrazine in diethylene glycol at 155°. 

Selective ketalization at C-3 in the presence of a 20-ketone is achieved by the selenium dioxide procedure, at room temperature with " or without an additional acid catalyst. 

Reactions of enamines with selenium dioxide gave low yields of enamino ketones (J8). Aromatization of cyclohexanone derived enamines eould be largely prevented by the use of aeetonitrile as solvent for the reaction. Even then, yields were eonsiderably below the limit of 50%, imposed by the generation of an equivalent of water. 

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... 

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. 

Dehydration of cortisone (198) affords the diene 199. This is then converted to ketal 200. The selectivity is due to hindrance about both the 11- and 20-carbonyl groups. The shift of the double bond to the 5,6-position is characteristic of that particular enone. Treatment of protected diene 200 with osmium tetroxide results in selective oxidation of the conjugated double bond at C-16,17 to afford the cis-diol (201). Reduction of the ketone at C-ll (202) followed by hydrolysis of the ketal function gives the intermediate 203. Selenium dioxide has been... 

A novel synthesis of 1,2,3-selenadiazoles 338 starts with the Michael addition of 2-nitropropane to a,P-unsaturated ketones 336 under basic conditions <06JHC149>. The resulting adducts are treated with semicarbazide hydrochloride to give semicarbazones 337, which are converted to 1,2,3-selenadiazoles 338 by reaction with selenium dioxide in THF (the choice of the solvent appears to be important in this case). 

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