A-Diketones oxidation

Aminotriazoles and their derivatives can be prepared from bis hydrazones and from substituted bis hydrazones of a-diketones. The bis hydrazones may in some cases be prepared more conveniently from -bromoketones than from a-diketones. Oxidation with mercuric oxide or with manganese dioxide gives the 1-aminotriazoles directly (Scheme m-ns Although two isomeric triazoles would be ex-... 

CgHjCOCHj + SeOa —> CgHgCOCHO + Se + H O This is one example of the oxidation by selenium dioxide of compounds containing a methylene group adjacent to a carbonyl group to thecorresponding a-ketoaldehyde or a-diketone (see also Section VII,23). 

Noncatalytic oxidation of propylene to propylene oxide is also possible. Use of a small amount of aldehyde in the gas-phase oxidation of propylene at 200—350°C and up to 6900 kPa (1000 psi) results in about 44% selectivity to propylene oxide. About 10% conversion of propylene results (214—215). Photochemical oxidation of propylene with oxygen to propylene oxide has been demonstrated in the presence of a-diketone sensitizers and an aprotic solvent (216). 

Monooximes of a-diketones have found applicability in the synthesis of 2-aminopyrazine 1-oxides by condensation with a-aminonitriles, and this reaction was used by White and coworkers in an approach to the synthesis of Cypridina etioluciferamine (Scheme 66 R = 3-indoloyl) (73T3761). In this instance, the use of TiCU as a catalyst was essential, since the carbonyl group in 3-acylindoles is normally deactivated and the required amine/carbonyl condensation is impractically slow. Under normal circumstances the carbonyl group in simple alkyl-substituted monoximes of a-diketones is the more reactive site and the reaction is rapid, requiring no catalysis (69LA(726)loo). 

Kubota and co-workers describe a novel oxidative rearrangement of the diosphenol (58) of 17iS-hydroxyandrost-4-ene-2,3-dione to the A-nor-A -1,2-diketone (59) in 33 % yield by the action of specially prep d manganese dioxide in boiling acetone. The rate of ring contraction is very sensitive to the source of the oxidant, and a trace of dilute sulfuric acid in the reaction mixture causes oxidative fission of ring A. 

Ring contraction by oxidative rearrangements of A-ring a-diketones by manganese dioxide... 

Electrolysis 1.5 V, CH.CN, H2O, LiC104 or Bu4N+C104 , 50-75% yield. " 1,3-Dithiolanes were not cleaved efficiently by electrolytic oxidation. This method has been applied to dithiane deprotection to produce a-diketones. ... 

They have also carried out the oxidation of selinene by means of ozone and potassium permanganate and have thus been able to establish that the regenerated selinene is not absolutely identical with the natural selinene. They are the first to record the existence of a hemi-cyclic-sesquiterpene this compound is termed pseudo-()3)-selinene. By passing a current of ozone into a solution of natural selinene (pseudo-( 8)-selinene). in acetic acid, there is obtained a diketone, CjjHogOj, which is purified by treatment with permanganate in acetone solution. Its properties are as. follows —... 

It has bsen prepared artificially by Semmler and McKenzie by oxidation of oxymethylene-menthone, CjjHjgO, a diketone, CjgHjgOg, resulting, which is inverted by means of alkalis to diosphenol. 

This reaction sequence is a general one for ene-diols. For example, in the same conditions, dihydroxyfumaric acid is oxidized by two moles of periodate, first to a diketone and then to two moles of oxalic acid (25,56). 

Internal alkynes have been oxidized to a-diketones by several oxidizing... 

Products detected or isolated from these oxidations include the corresponding a-hydroxy ketone and a-diketone and also adipic acid (from cyclohexanone) in up to 95 % yield. However, IrCI gives a-chloroketone in quantitative yield . Evidently when the rate of oxidation exceeds enolisation attack is on the keto form, probably via a complex, although this is definite only for Ce(IV) perchlorate, to give a radical, e.g. 

Enaminoketones undergo a clean oxidative cleavage to a-diketones, presumably through a dioxetane intermediate.180... 

Bis(ethylenediamine)gold(III) chloride reacts with /3-diketonates in aqueous base via Schiff base condensation to form complexes of gold(III) with a 14-membered macrocyclic tetraaza ligand such as (292).1711-1713 The X-ray structure showed the cation to be nearly planar. Delocalization of -electrons within the six-membered /3-diketonate rings was indicated by the observed pattern of C—C and C—N distances. Open-chain tetraaza ligand complexes in which condensation of only one /3-diketonate has occurred, can be isolated as intermediates in this reaction. They may be used for further condensation with a different /3-diketonate. Oxidation of this complex with trityl tetrafluoroborate introduces a double bond in position C2C3.1712,1714... 

An additional example of cycloamylose-induced catalysis which can probably be attributed to a microsolvent effect is the oxidation of a-hy-droxyketones to a-diketones (Scheme VIII). The rate of this oxidation is accelerated by factors ranging from 2.1 to 8.3 as the structure of the substrate is varied. As noted by Cramer (1953), these accelerations may be attributed to a cycloamylose-induced shift of the keto-enol equilibrium to the more reactive enol form. 

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