Dicarbonyl compounds by oxidation

The chromium trioxide-pyridine complex affords fair yields of dicarbonyl compounds by oxidation of suitably protected precursors 2,3 4,5-di-<3-isopropylidene-(2/f/e/n f/o-/l-D-(2ra/)/rtrt-hcxos-2-ulose-2,6-pyranose was thus prepared in 53% yield from 2,3 4,5-di-0-isopropylidene-/f-D-fructo-... 

Sometimes it is easier to make 1,3-dicarbonyl compounds by oxidation of... 

Dioxygenation of 1,2-Diones. 1,2-Cyclohexanedione derivatives have been converted to the corresponding 1,5-dicarbonyl compounds by oxidation with O2 employing copper(II) chloride as the catalyst. More recently, CuCl2-hydrogen peroxide has been used to prepare terminal dicarboxylic acids in high yield. While... 

The Corey Kim procedure is the oxidation method of choice for the transformation of (3-hydroxycarbonyl compounds into 1,3-dicarbonyl compounds. Treatment of (3-hydroxycarbonyl compounds under Corey Kim conditions leads to an intermediate 1,3-dicarbonyl compound 33 that reacts in situ with activated DMSO, resulting in the generation of a stable sulfur ylide 34. This sulfur compound can be transformed into the desired 1,3-dicarbonyl compound by reduction with zinc in acetic acid.254... 

Ideally made by this strategy from 1,4-dicarbonyl compounds with oxidation nh2 4 R2 V R2 V... 

Katayama, S., Fukuda, K., Watanabe, T., Yamauchi, M. Synthesis of 1,3-dicarbonyl compounds by the oxidation of 3-hydroxycarbonyl compounds with Corey-Kim reagent. Synthesis 1988,178-183. 

The phase-transfer-assisted permanganate oxidation of alkynes and alkenes has been reviewed. Terminal and internal alkynes are oxidized to 1,2-dicarbonyl compounds by the combined action of diphenyl disulphide, ammonium peroxidisulphate and water or by sodium periodate in the presence of ruthenium dioxide (equation 34). Other reagents for the conversion of acetylenes into 1,2-dicarbonyl compounds are hydrogen peroxide in the presence of (2,6-dicarboxylatopyridine)iron(II), the complex oxo(A, A -ethylenebissalicylideneiminato)chromium(V) trifluoromethanesulphonate (216)and ruthenium tetroxide as a mediator in electrooxidation. l-Acetoxyalkan-2-ones 217 are obtained by the oxidation of terminal acetylenes with sodium perborate and mercury(II) acetate in acetic acid ". Terminal alkynes give a-ketoaldehydes 218 on treatment with dilute hydrogen peroxide, combined with mercury(II) acetate and sodium molybdate or sodium tungstate under phase-transfer conditions. ... 

The Wacker reaction provides a method for the preparation of 1,4-dicarbonyl compounds, by formation of an enolate, allylation with an allyl halide, followed by palladium-catalysed oxidation of the terminal alkene. The product 1,4-dicarbonyl compounds can be treated with base to promote intramolecular aldol reaction (Robinson annulation - see Section 1.1.2) to give cyclopentenones. Thus, in a synthesis of pentalenene, Wacker oxidation of the 2-aUyl ketone 115 gave the 1,4-diketone 116, which was converted to the cyclopentenone 117 (5.115). ... 

Oxidation of j8-dicarbonyl compounds by f-butyl hydroperoxide in the presence of vanadyl acetylacetonate [VO(acac)2] in benzene results in decomposition of the carbon skeleton, via intermediate trioxo derivatives." ... 

Pyrroles, pyrazoles, imidazoles, furans, and thiophenes can be made from 1,3-dicarbonyl compounds by reaction with an appropriate amine, oxidizing agent, or This process is... 

The formation of dicarbonyl compounds by this reagent is a variation of the Kornblum oxidation and presumably involves acid-catalyzed iodination of the carbonyl compound (1) to give an a-iodo ketone (2) which undergoes displacement by DMSO to... 

Oxadiazole-2-oxides (furoxans) are generated by oxidative cychzation of the dioximes of 1,2-dicarbonyl compounds. As oxidants, NaOCl, Pb(OAc)4, or N2O4 have proved useful electrochemical oxidation is also possible [472]. 

The direct oxidative annulations with alkynes by Csp -H/Csp -H bond cleavage have not been developed yet only two examples were described in this area using nickel(O) by Hiyama [198] and rhodium(lll) by Wang [199]. With ruthenium (11) catalyst, Lam reported the first annulations with alkynes of 2-aryl-l,3-dicarbonyl compounds by Csp -H and Csp -H bond activation [200]. The reaction of 2-aryl-3-hydroxy-2-cyclohexenones and cyclic 2-aryl-l,3-dicarbonyl compounds with 2.5 mol% of [RuCl2(/ -cymene)]2 and 2.2 equiv. of Cu(OAc)2 was performed in 1,4-dioxane at 90°C, and led to spiroindene derivatives in 50-84%... 

The oxidative mono- or diallylation of 1,3-dicarbonyl compounds by allylic silanes proceeds in the presence of VO(OEt)Cl2 as shown in Scheme 2.53 [116]. The 1,3-dicarbonyl compounds formally act as electrophiles in this oxidative carbon-carbon bond forming reaction. 

Cerium(III) chloride heptahydrate has been used by Christoffers and coworkers as a catalyst for the a-hydroxylation of /3-dicarbonyl compounds by molecular oxygen (Christoffers and Werner, 2002 Christoffers et al., 2003a). The reaction is useful for the hydroxylation of cyclic /3-dicarbonyl compounds, but many side reactions occur with acyclic -dicarbonyl (scheme 60). The byproducts include a-chlorinated /3-dicarbonyl compounds. In the proposed reaction mechanism, cerium(III) coordinates to a /3-dicarbonyl ligand (scheme 61). The coordinated cerium(III) (L Ce + in scheme 61) is oxidized by molecular oxygen to cerium(IV). 

Enamino-ketones and enamino-lactones have been converted into the corresponding a-dicarbonyl compounds by photo-oxygenation via dioxetan intermediates. Finally, the photo-oxidation of pyrroles has been studied... 

Compounds with a A -bond (131) are used more frequently, one of the methods of synthesizing these compounds starting from D-homo ketones with the keto group at C17. The oxidation of (131) leads either to dialdehydes (132 R = H) or to ketoaldehydes (132 R = Me, CH2OAC). The re-cyclization of these dicarbonyl compounds by the action of bases gives products of type (133 R =H, Me, CH2OAC) containing a one-carbon or two-carbon side chain at C17 (Schemes 52, 53, 67, 77, 107-109, 111, 112). 

Oxidation of Activated C-H Bonds. As shown in eq 13, extensive oxidation adjacent to carbonyl groups is possible with SOCI2 under relatively mild conditions. The process often stops after formation of the a-chlorosulfenyl chloride. Remarkably, these may be easily hydrolyzed back to the carbonyl compounds from which they were derived. Alternatively, they may be treated with a secondary amine such as morpholine followed by hydrolysis to yield the a-dicarbonyl compound. Similar oxidation of acid derivatives during acid chloride formation is possible (see above). 

The most general methods for the syntheses of 1,2-difunctional molecules are based on the oxidation of carbon-carbon multiple bonds (p. 117) and the opening of oxiranes by hetero atoms (p. 123fl.). There exist, however, also a few useful reactions in which an a - and a d -synthon or two r -synthons are combined. The classical polar reaction is the addition of cyanide anion to carbonyl groups, which leads to a-hydroxynitriles (cyanohydrins). It is used, for example, in Strecker s synthesis of amino acids and in the homologization of monosaccharides. The ff-hydroxy group of a nitrile can be easily substituted by various nucleophiles, the nitrile can be solvolyzed or reduced. Therefore a large variety of terminal difunctional molecules with one additional carbon atom can be made. Equally versatile are a-methylsulfinyl ketones (H.G. Hauthal, 1971 T. Durst, 1979 O. DeLucchi, 1991), which are available from acid chlorides or esters and the dimsyl anion. Carbanions of these compounds can also be used for the synthesis of 1,4-dicarbonyl compounds (p. 65f.). 

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). 

Cyclic diols give dicarbonyl compounds The reactions are faster when the hydroxyl groups are cis than when they are trans but both stereoisomers are oxidized by periodic acid... 

The conversion of furans by oxidative acetylation or methoxylation to 2,5-diacetoxy- or 2,5-dimethoxy-2,5-dihydrofurans respectively, and their subsequent hydrogenation to the corresponding tetrahydrofurans, provides a useful source of protected 1,4-dicarbonyl compounds capable of conversion inter alia into the other five-membered heterocycles [Pg.142]

The rapid synthesis of heteroaromatic Hantzsch pyridines can be achieved by aromatization of the corresponding 1,4-DHP derivative under microwave-assisted conditions [51]. However, the domino synthesis of these derivatives has been reported in a domestic microwave oven [58,59] using bentonite clay and ammoniiun nitrate, the latter serving as both the source of ammonia and the oxidant, hi spite of some contradictory findings [51,58,59], this approach has been employed in the automated high-throughput parallel synthesis of pyridine libraries in a 96-well plate [59]. In each well, a mixture of an aldehyde, ethyl acetoacetate and a second 1,3-dicarbonyl compound was irradiated for 5 min in the presence of bentonite/ammonium nitrate. For some reactions, depending upon the specific 1,3-dicarbonyl compound used. 

---