Vicinal Dicarbonyls

Oxamic acid 26 and AT-hydroxyoxamic acid 27 derivatives were disclosed by the Boehringer Ingelheim group as moderately active Lck SH2 domain antagonists [119,130]. 

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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],... 

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. 

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]. 

The imines derived from vicinal dicarbonyl substances afford cis-lactams (Scheme 2), whereas the imines prepared from aryl and alkenyl aldehydes yield trans-lactams (Schemes 3 and 4). The different basis for the stereoselection in the carbonylative cycloaddition from that of the usual base-induced process is worthy of anphasis. The mechanism of this carbonylative formal [2 + 2] cycloaddition is discussed in comparison with the results of the base-induced ketene-imine cycloaddition,... 

Other Reactions and Features of Glycosides.—The degradation of methyl glycosides in oxygenated, aqueous 0.5 M sodium hydroxide at 120 °C has been investigated. The principal products were formed by way of benzilic acid rearrangement of vicinal dicarbonyl intermediates. 

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. 

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. 

Oxidations. Aikynes of high nucleophilicity such as ethoxy-(trimethylsilyl)acetylene react with electrophilic O3 to give vicinal dicarbonyl derivatives. In contrast to alkylated or ary-lated acetylenes, neither products of complete C-C cleavage nor peroxidic materials were detected as primary products. Ethoxy-(trimethylsilyl)acetylene reacted with ozone to yield a mixture of ethyl 2-oxo-2-(trimethyl)acetate (13) and ethyl trimethylsUyl oxalate (14) (eq 11). The mechanism of this reaction was also discussed. ... 

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