Diketones by oxidation

The functionalized [4]radialene 86 offers opportunities for further transformations by hydrolytic cleavage of the O-silylenol moieties and by oxidative desilylation (Scheme 16). Base- and acid-catalyzed hydrolyses lead to different products (130 and 131, respectively)60. By analogy with the formation of 1,4-diketones by oxidative coupling of two siloxyalkene molecules, treatment of 86 with the iodonium salt Phl+—O—+I—Ph BF4 in dichloromethane leads to 132 which is immediately... 

Diketones (8, 126 127). Complete details of the synthesis of 1,4-diketones by oxidative coupling of ketone enolales and trimethylsilyl enol ethers with Cu(OTf)2 are available.1 Use of isobutyronitrile is essential for the coupling it is not only a suitable solvent, but the nitrile group apparently facilitates reduction of the intermediate copper enolate to CuOTf.2 When acetonitrile is used by-products containing a nitrile group are formed. 1,4-Diketones are formed only in traces when DMF, DMSO, or HMPT is used. 

An Og-Oa-stream passed 2 hrs. at ca. -70° into a methanolic soln. of %-syn-methoxy- A2c/o-tricyclo[3.2.1.02,4]oct-6-ene, excess Og removed with N2, the cold soln. treated with dimethyl sulfide, trimethyl orthoformate, and methanol containing HCl, the cooling bath removed, and stirred overnight -> 2-endo,4-endo-bis(dimethoxymethyl)-3-exo-methoxybicyclo[3.1.0]hexane. Y 93-96%. F. e. s. F. Frickel, Synthesis 1974, 507 also different reaction course s. B. 108, 831 (1975) diketones by oxidative ring opening s. J. Ficini and J. P. Genet, Tetrah. Let. 1975, 2633 a-hydroxy-y-diketones from cyclobut-2-enols s. Bl. 1975, 1811. 

Scheme 6.62. A representation of the conversion of an internal (i.e., nonterminal) alkyne to an a-diketone by oxidation with neutral permanganate (Mn04"). Although two equivalents of permanganate (Mn04 ) are shown, the second equivalent is not known to be necesary to remove the proton. The manganese in HMnOs eventually undergoes disproportionation and...

Internal alkynes are oxidized to acytoins by thalliuin(III) in acidic solution (A. McKil-lop, 1973 G.W. Rotermund, 1975) or to 1,2-diketones by permanganate or by in situ generated ruthenium tetroxide (D.G. Lee, 1969, 1973 H. Gopal, 1971). Terminal alkynes undergo oxidative degradation to carboxylic acids with loss of the terminal carbon atom with these oxidants. 

Several 1,4-dicarbonyl compounds are prepared based on this oxidation. Typically, the 1,4-diketone 10 or the 1,4-keto aldehyde 12 can be prepared by the allylation of a ketone[24] or aldehyde[61,62], followed by oxidation. The reaction is a good annulation method for cyclopentenones (11 and 13). Syntheses of pentalenene[78], laurenene[67], descarboxyquadrone[79], muscone (14 R = Me)[80]) and the coriolin intermediate 15[71] have been carried out by using allyl group as the masked methyl ketone (facing page). 

Tris(2,4-pentanedionato)iron(III) [14024-18-1], Fe(C H202)3 or Fe(acac)3, forms mby red rhombic crystals that melt at 184°C. This high spin complex is obtained by reaction of iron(III) hydroxide and excess ligand. It is only slightly soluble in water, but is soluble in alcohol, acetone, chloroform, or benzene. The stmcture has a near-octahedral arrangement of the six oxygen atoms. Related complexes can be formed with other P-diketones by either direct synthesis or exchange of the diketone into Fe(acac)3. The complex is used as a catalyst in oxidation and polymerization reactions. 

Diketones can be prepared by oxidation of the corresponding monoketone (287) or a-hydroxyketone (288). 1,2-Diketones are used extensively as intermediates in the preparation of pharmaceuticals, flavors, and fragrances. Toxicity data for selected diketones are shown in Table 11. 

Hexanedione [110-13-4] (acetonylacetone) is one of the most widely used 1,4-diketones. It is a colorless high boiling Hquid prepared by the hydrolysis of 2,5-dimethylfuran (332,333), by oxidation of 2,5-hexanediol (334) or 5-hexen-l-one (335), and from allylacetone (336). Its main use is in solvent systems and as a raw material for chemical synthesis. It is reportedly not highly toxic (336). 

Acyloins are useful starting materials for the preparation of a wide variety of heterocycles (e.g., oxazoles and imidazoles ) and carbocyclic compounds (e.g., phenols ). Acyloins lead to 1,2-diols by reduction, and to 1,2-diketones by mild oxidation. 

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

Diaza-l,6-dioxa-6fl-tellurapentalenes 97 were obtained in 4—60% yields by oxidation of 1,3-diketone dioximes with tellurium dioxide (79BSF199). 

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. 

A two-step procedure was required for the preparation of a diverse set of pyrrole-3-carboxylic acid derivatives. The diketone 15 was prepared using a functional homologation of a 6-ketoester 14 with different aldehydes followed by oxidation with PCC. The Paal-Knorr reaction was carried out in AcOH in a sealed tube under microwave irradiation (180 °C, 5-10 min) to give differently substituted pyrroles with a COOMe group in position 3 (Scheme 5). This group was further transformed to expand the diversity of the products prepared with this method [32]. 

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

The reaction of the aldehyde 174, prepared from D-glucose diethyl dithio-acetal by way of compounds 172 and 173, with lithium dimethyl methyl-phosphonate gave the adduct 175. Conversion of 175 into compound 176, followed by oxidation with dimethyl sulfoxide-oxalyl chloride, provided diketone 177. Cyclization of 177 with ethyldiisopropylamine gave the enone 178, which furnished compounds 179 and 180 on sodium borohydride reduction. 0-Desilylation, catalytic hydrogenation, 0-debenzyIation, and acetylation converted 179 into the pentaacetate 93 and 5a-carba-a-L-ido-pyranose pentaacetate (181). 

There are also reactions in which electrophilic radicals react with relatively nucleophilic alkenes. These reactions are exemplified by a group of procedures in which a radical intermediate is formed by oxidation of readily enolizable compounds. This reaction was initially developed for /3-ketoacids,311 and the method has been extended to jS-diketones, malonic acids, and cyanoacetic acid.312 The radicals formed by the addition step are rapidly oxidized to cations, which give rise to the final product by intramolecular capture of a carboxylate group. 

Triphenylformazan behaves as a bidentate ligand forming 2 1 complexes (217) with divalent copper, nickel, and cobalt.377 Formazan metal complexes can be compared to complexes of azo dyes or beta diketones due to structural similarity.301,302 In general, formazan metal complexes have low stability toward acids. However, when electron-donating substituents are added to the aromatic ring, a considerable enhancement in stability is observed. Cationic complexes of type 218 are also known. The complexation of formazan with metal cation can be accompanied by oxidation to the tetrazolium salt and the formation of a complex... 

Edegger, K., Stampfer, W., Seisser, B. et al. (2006) Regio- and stereoselective reduction of diketones and oxidation of diols by biocatalytic hydrogen transfer. European Journal of Organic Chemistry, (8), 1904—1909. 

Oxidation of p-hydroxy ketones. Reaction of the Corey-Kim reagent with these substrates can result in dimethylsulfonium dicarbonylmethylides in 80-98% yield. These S-ylides are desulfurized to p-diketones by zinc in acetic acid, p-... 

Hydroxy ketones that are mono- or disubstituted at the a-position are oxidized directly to 1,3-diketones by the reagent in moderate to good yield. 

Since enol silyl ethers are readily accessible by a number of methods in a regioselective manner and since the trialkylsilyl moiety as a potential cationic leaving group facilitates the termination of a cyclization sequence, unsaturated 1-trialkylsilyloxy-1-alkenes represent very promising substrates for radical-cation cyclization reactions. Several methods have been reported on the synthesis of 1,4-diketones by intermolecular oxidative coupling of enol silyl ethers with Cu(II) [76, 77], Ce(IV) [78], Pb(IV) [79], Ag(I) [80] V(V) [81] or iodosoben-zene/BFa-etherate [82] as oxidants without further oxidation of the products. 

Correlation of structure and reactivity in the oxidation of substituted aromatic anils by pyridinium fluorochromate (PFC) has been attempted using Grunwald-Winstein and Hammett equations. The stoichiometry between the substrate and oxidant is 1 2 in the oxidation of cyclic ketones by PFC to 1,2-diketones. PFC oxidation of secondary alcohols has been investigated. ... 

A convenient preparation has been reported for benzofuran annulated 2-phenyl-l,5-benzothiazepine derivatives 318 by oxidative cyclocondensation of phenolic diketones 317 with o-aminothiophenol in DMSO (Equation (36) (2000M393)). 

---