Vicinal dicarbonyl compounds

Selenium dioxide, Se02 (mp 315 °C, sublimes), and selenious acid, H2Se03, which is obtained by the evaporation of an aqueous solution of Se02 [507, 50S], are very selective oxidants. They are capable of mild dehydrogenation to form double bonds [375] and can oxidize alkenes and acetylenes to vicinal dicarbonyl compounds [509, 510] and allylic ethers to aldehydes [511]. The most important applications are conversions of alkenes into allylic alcohols [5i2] of benzylic, methyl, or methylene groups into carbonyl groups [513, 514, 5i5] and of carbonyl compounds into a-... 

The applications of ruthenium tetroxide range from the common types of oxidations, such as those of alkenes, alcohols, and aldehydes to carboxylic acids [701, 774, 939, 940] of secondary alcohols to ketones [701, 940, 941] of aldehydes to acids (in poor yields) [940] of aromatic hydrocarbons to quinones [942, 943] or acids [701, 774, 941] and of sulfides to sulfoxides and sulfones [942], to specific ones like the oxidation of acetylenes to vicinal dicarbonyl compounds [9JS], of ethers to esters [940], of cyclic imines to lactams [944], and of lactams to imides [940]. 

Alkenes may also be transformed into vicinal dicarbonyl compounds. The treatment of alkenes with selenium dioxide, although possible, does not give satisfactory yields [509]. Better results are obtained when unsaturated compounds such as oleic acid are oxidized with potassium permanganate buffered with acetic anhydride [861],... 

Vinyl ketene (392) is generated by the carbonylation of the allyl phosphate 390 in the presence of a base as shown by 391. A useful application of the ketene formation is the synthesis of -lactam skeleton by [2 -I- 2] cycloaddition of the ketene with imines. Thus, reaction of the imine 393, derived from vicinal dicarbonyl compounds, with the ketene 392 afforded cw-lactam 394 [152], On the other hand, the transAacism 397 was obtained by the carbonylation of the allyl phosphates 395 in the presence of the imine 396 derived from aldehyde [153]. 

Ethyl carbamate can also be produced in small quantities by other reactions, for example from vicinal dicarbonyl compounds, such as methylglyoxal, biacetyl and pentane-2,3-dione, which are byproducts of fermentation (see Section 8.2.2.1.3). Some dicarbonyl compounds may arise by fragmentation of sugars. 

Azine approach. Cyclization of the oxime (48) (73G219) corresponds to a common method for the preparation of isoxazoles, viz. the reaction between 1,3-dicarbonyl compounds and hydroxylamine. Similarly a cyano group reacts with hydroxylamine to form an N-hydroxyamidine which can be cyclized to an isoxazole if the vicinal carbon is activated and carries a leaving group. The 5-cyanopyrimidine (49) perhaps behaves unexpectedly in that it is a trichloromethyl substituent which is the leaving group in the cyclization (79JHC11-09). This behavior may be attributed to its location in the activated pyrimidine 4-position. 

Scheme 40. Phenylselenyl Sulfate Catalyzed One-Pot Conversions of Dicarbonyl Compounds into Vicinal Monoprotected Tricarbonyl and Diprotected Tetracarbonyl Compounds...

Sodium bismuthate, NaBiOs, cleaves vicinal diols to dicarbonyl compounds [482, 483] but offers no advantage over the more common oxidants of vicinal diols, such as lead tetraacetate and periodic acid. 

The oxidative cleavage of carbon-carbon bonds in vicinal diols [756, 759] is a reaction widely used in saccharide chemistry. Besides its application in this reaction, periodic acid achieves the oxidative coupling [757] or oxidation to quinones [758] of polynuclear aromatic hydrocarbons, the oxidation of methyl groups in aromatic compounds to carbonyl groups [760], the conversion of epoxides into dicarbonyl compounds [761], and the oxidative cleavage of trimethylsilyl ethers of acyloins to carboxylic acids [755]. 

Acetyl hypoiodite (iodine acetate), CH3COOI, is prepared by treatment of silver acetate in acetic acid with iodine at room temperature [779, 780], The reagent cleaves vicinal diols to dicarbonyl compounds [779] and degrades tertiary alcohols to ketones [780], Acetyl hypoiodite is also an intermediate in the reaction of alkenes with the so-called Simonini complex, an addition product of iodine with 2 mol of silver acetate [781, 782, 783],... 

The spectrum of applications of potassium permanganate is very broad. This reagent is used for dehydrogenative coupling [570], hydrox-ylates tertiary carbons to form hydroxy compounds [550,831], hydroxylates double bonds to form vicinal diols [707, 296, 555, 577], oxidizes alkenes to a-diketones [560, 567], cleaves double bonds to form carbonyl compounds [840, 842, 552] or carboxylic acids [765, 841, 843, 845, 852, 869, 872, 873, 874], and converts acetylenes into dicarbonyl compounds [848, 856, 864] or carboxylic acids [843, 864], Aromatic rings are degraded to carboxylic acids [575, 576], and side chains in aromatic compounds are oxidized to ketones [566, 577] or carboxylic acids [503, 878, 879, 880, 881, 882, 555]. Primary alcohols [884] and aldehydes [749, 868, 555] are converted into carboxylic acids, secondary alcohols into ketones [749, 839, 844, 863, 865, 886, 887], ketones into keto acids [555, 559, 590] or acids [559, 597], ethers into esters [555], and amines into amides [854, 555] or imines [557], Aromatic amines are oxidized to nitro compounds [755, 559, 592], aliphatic nitro compounds to ketones [562, 567], sulfides to sulfones [846], selenides to selenones [525], and iodo compounds to iodoso compounds [595]. 

The oxidative cleavage of epoxides with hydrogen peroxide gives vicinal hydroxy hydroperoxides [178]. With dimethyl sulfoxide in the presence of trifluoromethanesulfonic acid and diisopropylethylamine, epoxides are converted into a-hydroxy ketones [1014], and with periodic acid, dicarbonyl compounds are formed [761] (equations 343 and 344). 

Most information on cyclocondensation reactions of ZV-aminoazoles is concerned with vicinal N.C-diaminoazoles. In most cases, reactions were carried out with various carbonyl-containing compounds carboxylic acids and their derivatives, aldehydes and ketones, 1,2- an 1,3-dicarbonyl compounds, etc. Depending on the structure of these synthons, cyclocondensations lead to the formation of five-, and six- or seven-membered heterocycles. 

The photochemistry of o-quinones and non-enolic a-diketones has a venerable history dating at least to 1886 when Klinger 82> reported sunlight irradiations of benzil and 9,10-phenanthrenequinone. The latter compound and biacetyl have been extensively investigated for many years and interest has broadened to embrace a wide variety of substances. The basic processes involved depend in large measure on the presence of the vicinal dicarbonyl system rather than on classification as diketone or o-quinone it appears both justified and desirable to consider their photochemistry jointly. a-Diketones which exist in the enolic form behave for the most part as substituted a,/9-unsaturated ketones and will not be considered. For convenience, the term dione will be used when reference is intended to both a-diketones and o-quinones. 

Reactions of 1,2-Diketones and other 1,2-Dicarbonyl Compounds. - 1,2-Dicarbonyl compounds such as glyoxal and biacetyl have been irradiated under direct sunlight. A study has examined the wavelength dependence for fission of glyoxal into the CHO radical on irradiation in the 290-420 nm range. a-Fission is the principal photochemical reaction of vicinal cyclic tricarbonyl compounds such as indanetriones. ... 

Like other vicinal dicarbonyl derivatives of sugars, dehydroascorbic acid is involved in the MaiUard reaction. Dehydroascorbic acid (or its bicyclic hydrate. Figure 5.27) is a y-lactone that is readily hydrolysed under a base catalysis to its parent unstable compound that undergoes a series of irreversible reactions. These reactions result in loss of vitamin C and the formation of coloured products, and the discoloration of fruit and vegetable products. 

---