Dicarbonyl compounds Copper oxide

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... 

Organometallic reagents and catalysts continue to be of considerable importance, as illustrated in several procedures CAR-BENE GENERATION BY a-ELIMINATION WITH LITHIUM 2,2,6,6-TETRAMETHYLPIPERIDIDE l-ETHOXY-2-p-TOL-YLCYCLOPROPANE CATALYTIC OSMIUM TETROXIDE OXIDATION OF OLEFINS PREPARATION OF cis-1,2-CYCLOHEXANEDIOL COPPER CATALYZED ARYLA-TION OF /3-DICARBONYL COMPOUNDS 2-(l-ACETYL-2-OXOPROPYL)BENZOIC ACID and PHOSPHINE-NICKEL COMPLEX CATALYZED CROSS-COUPLING OF GRIG-NARD REAGENTS WITH ARYL AND ALKENYL HALIDES 1,2-DIBUTYLBENZENE. 

Alkyl- or aryl-substituted pyrazole 1-oxides 94 can be obtained in acceptable yields by oxidative cyclization of O-silylated 3-oximimines like 1 -tert-hutyldimethyIsilyloxy-4-methylamino-1 -azab nta-1,3-diene 93 using copper(II) sulfate as the oxidant and pyridine and acetonitrile as the solvent. The oximimines are prepared from 1,3-dicarbonyl compounds 92 in a one-pot process. The method also gives access to 2-alkyl and aryl-pyrazole 1-oxides R=H devoid of substituents at the ring carbon atoms (94 Ri = R2=H) (1995JCS(P1)2773) (Scheme 27). 

The condensation of a, dicarbonyl compounds (49) with aj3-diamino compounds (50), which proceeds through the dihydropyrazine (51), has been much used for the synthesis of alkyl- and arylpyrazines (52). These reactions are usually carried out in methanol, ethanol, or ether in the presence of sodium or potassium hydroxide. The dihydropyrazines may be isolated, or oxidized directly to the pyrazine. Dehydrogenating agents that have been employed include oxygen in aqueous alkali (329), air in the presence of potassium hydroxide (330), sodium amylate in amyl alcohol (330a), alcoholic ferric chloride (24), and copper chromite catalyst at 300° (331) (see also Section 1). Pyrazines prepared by this method and modifications described below are listed in Table II.8 (2, 6, 24, 60, 80,195, 329-382) and some additional data are provided in Sections VI. 1 A, VlII.lA(l), and IX.4A(1). 

Oxidative addition of elemental fluorine to appropriate 1,3-dicarbonyl compounds provides a convenient synthesis of perfluorinated 1,2-dioxolanes. In this way (20) may be formed from difluoromalonyl fluoride, F2C(COF)2 <92JST(274)163>, and (39) is similarly prepared from either hexafluoroacetylacetone or the copper(II) or nickel(II) chelate of trifluoroacetylacetone with concomitant replacement of all remaining hydrogen atoms by fluorine <65JOCI429>. 

Addition to aldehydes, ketones, and enones occurs cleanly at the carbonyl group, e.g. to give 86, but the copper derivative adds to enones in the expected Michael sense (chapter 9) to give 1,6-dicarbonyl compounds such as 88 after oxidation. Cyclisation to 89 completes a cyclo-pentannelation sequence (chapter 6). 

Copper(II) salts are efficient one-electron oxidants for the generation of radicals from lithium enolates [1]. This concept was successfully applied for the oxidative coupling of ketones or amides 36 to afford the corresponding 1,4-dicarbonyl compounds 37 in good yield [17]. If an optically active imidazolidinone is used as chiral auxiliary, the reaction exhibits an excellent simple and induced diastereoselectivity (Scheme 12). 

In 2008, using an inexpensive copper salt as the catalyst, Powell and coworkers developed the oxidative coupling of benzylic C-H bonds with 1,3-dicarbonyl compounds (Scheme 3.17). Kinetic isotope studies support a mechanism involving a benzylic H-atom abstraction. 

Many of the classical methods grew out of the earliest synthesis of imidazole, which was achieved in 1858 by Debus [1] when he allowed glyoxal, formaldehyde and ammonia to react together. Although the earliest modifications of this method used a-diketones or a-ketoaldehydes as substrates [2, by the 1930s it was well established that a-hydroxycarbonyl compounds could serve equally well, provided that a mild oxidizer (e.g. ammoniacal copper(ll) acetate, citrate or sulfate) was incorporated [3. A further improvement was to use ammonium acetate in acetic acid as the nitrogen source. All of these early methods have deficiencies. There are problems associated with the synthesis of a wide range of a-hydroxyketones or a-dicarbonyls, yields are invariably rather poor, and more often than not mixtures of products are formed. There are, nevertheless, still applications to the preparation of simple 4-alkyl-, 4,5-dialkyl(diaryl)- and 2,4,5-trialkyl(triaryl)imidazoles. For example, pymvaldehyde can be converted quite conveniently into 4-methylimidazole or 2,4-dimethylimidazole. However, reversed aldol reactions of pyruvaldehyde in ammoniacal solution lead to other imidazoles (e.g. 2-acetyl-4-methylimidazole) as minor products [4]. Such... 

The reaction of dimedone (39) with tetraphenylbismuthonium derivatives and BTMG gave the a,a-diphenyl derivative (40). But when dimedone (39) was treated with triphenylbismuth carbonate, an ylide (41) was obtainedP This ylide was later isolated as a stable crystalline compound. This ylide (41) can also be prepared by reaction of the sodium salt of dimedone either with triphenylbismuth dichloride or with triphenylbismuth oxide. Similarly, Meldrum s acid gave the corresponding bismuthonium ylide with triphenylbismuth carbonate and with triphenylbismuth dichloride.3 36 uch ylides can also be made by decomposition of the appropriate dicarbonyl diazonium derivative in the presence of triphenylbismuthane catalysed by bis(hexafluoroacetylacetonato)copper (II) 37 These ylides react with aldehydes to give cyclopropanes, dihydrofurans and a,p-unsaturated carbonyl... 

Copper(ll) acetate performs a double role activation of the triacyl methane group by coordination and production of the reactive triacylmethyl radical by a coupled redox reaction. The proposed mechanism is supported by the fact that 274 is present in the auto-oxidation reaction mixture of hexahydrocolupulone, while compounds 275-279 are absent. Auto-oxidation occurs indeed at the ring carbon atom C-4 (see 13.1.2.). The radicals are in this case produced within the 1,3-dicarbonyl system in the ring, whereby only 274 can be formed in an analogous way as described before (pathway B). 

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