A-Ketoaldehydes 3

CgHjCOCHj + SeOa —> CgHgCOCHO + Se + H O This is one example of the oxidation by selenium dioxide of compounds containing a methylene group adjacent to a carbonyl group to thecorresponding a-ketoaldehyde or a-diketone (see also Section VII,23). 

Adducts from various quaternary salts have been isolated, in reactions with aldehydes, a-ketoaldehydes, dialkylacylphosphonates and dialkyl-phosphonates, isocyanates, isothiocyanates, and so forth (Scheme 15) (36). The ylid (11) resulting from removal of a Cj proton from 3.4-dimethyl-S-p-hydroxyethylthiazolium iodide by NEtj in DMF gives with phenylisothiocyanate the stable dipolar adduct (12) that has been identified by its NMR spectrum and reactional product, such as acid addition and thiazolidine obtention via NaBH4 reduction (Scheme 16) (35). It must be mentioned that the adduct issued from di-p-tolylcarbodiimide is separated in its halohydrogenated form. An alkaline treatment occasions an easy ring expansion into a 1,4-thiazine derivative (Scheme 17) (35). 

Synthesis of ptendines from diaminopyrfmidines and a-diketones or a-ketoaldehydes. 

The coupling of enamines with aromatic diazonium salts has been used for the syntheses of monoarylhydrazones of a-diketones (370,488-492) and a-ketoaldehydes (488,493). Cleavage of the initial enamine double bond and formation of the phenylhydrazone of acetone and acetophenone has been reported with the enamines of isobutyraldehyde and 2-phenylpropionalde-hyde. Rearrangement of the initial coupling product to the hydrazone tautomer is not possible in these examples. 

KCN, 226,229, 233, 234, 238 Keroplatus, 337 a-Keto acid, 173 a-Ketoaldehyde, 176 Kolga, 336 Kolga kyalina, 301 Krill See Euphausiids Krill luciferase (Protein P), 71, 79, 343 assay, 73... 

As far as we are aware, the azo coupling of an ethyne derivative was only investigated over half a century ago Ainley and (Sir Robert) Robinson (1937) investigated the reaction of phenylethynes (phenylacetylenes) with diazonium ions (Scheme 12-59). Unsubstituted phenylethyne did not give identifiable products with the 4-nitrobenzenediazonium ion, but with the more nucleophilic 4-methoxyphenyl-ethyne an azo compound (12.119) was formed. On reaction with water it gives an arylhydrazone of an a-ketoaldehyde (12.120). 

Scheme 16 Hydrogen-mediated coupling of 1,3-cyclohexadiene to a-ketoaldehydes...

Reaction of 6-aminopyrimidines with 2 mol of a-ketoaldehyde in aqueous medium gave rise to the zwitterionic a-iminocarboxylic acids thus, 214 with methylglyoxal gave the pyrimido[l,6- ]pyrimidin-2-carboxylic acid 215 (Equation 26) <2005W02005/039589>. 

Intramolecular oxonium ylide formation is assumed to initialize the copper-catalyzed transformation of a, (3-epoxy diazomethyl ketones 341 to olefins 342 in the presence of an alcohol 333 . The reaction may be described as an intramolecular oxygen transfer from the epoxide ring to the carbenoid carbon atom, yielding a p,y-unsaturated a-ketoaldehyde which is then acetalized. A detailed reaction mechanism has been proposed. In some cases, the oxonium-ylide pathway gives rise to additional products when the reaction is catalyzed by copper powder. If, on the other hand, diazoketones of type 341 are heated in the presence of olefins (e.g. styrene, cyclohexene, cyclopen-tene, but not isopropenyl acetate or 2,3-dimethyl-2-butene) and palladium(II) acetate, intermolecular cyclopropanation rather than oxonium ylide derived chemistry takes place 334 ). 

Fischer1-2 decided that the mode of formation, the reactions with hydrazines, aromatic diamines, and oxidizing agents, and the reduction to D-fructose could be explained by attributing to the open-chain form of D-glucosone the a-ketoaldehyde structure L. 

Intermolecular cross aldolization of metallo-aldehyde enolates typically suffers from polyaldolization, product dehydration and competitive Tishchenko-type processes [32]. While such cross-aldolizations have been achieved through amine catalysis and the use of aldehyde-derived enol silanes [33], the use of aldehyde enolates in this capacity is otherwise undeveloped. Under hydrogenation conditions, acrolein and crotonaldehyde serve as metallo-aldehyde enolate precursors, participating in selective cross-aldolization with a-ketoaldehydes [24c]. The resulting/ -hydroxy-y-ketoaldehydes are highly unstable, but may be trapped in situ through the addition of methanolic hydrazine to afford 3,5-disubstituted pyridazines (Table 22.4). 

Table 22.5 Catalytic reductive coupling of 1,3-cyclohexadiene with alkyl, aryl and heteroaryl a-ketoaldehydes.

The reductive coupling of 1,3-cyclohexadiene and a-ketoaldehydes, which occurs without over-reduction of the olefmic product, suggests the feasibility of utilizing more highly unsaturated pronucleophiles in the form of 1,3-enynes. In the... 

Table 22.8 Regioselective reductive coupling of non-symmetric 1,3-diynes to various a-ketoaldehydes.

Polyphenylquinoxalines (PPQ) are obtained by the polymerization of aromatic bis-o-diamine and bis-a-ketoaldehyde reactants in m-cresol at 80°C [Hergenrother, 1988 Klein et al., 2001] ... 

Reaction of (-)-a-pinene (1) with stoich. RuO /CCl gave a ketoaldehyde (2), probably via a Ru(VI) diester (4). If the reaction is performed using RuO in acetone rather than CCl, the a-ketol (3) is the main product. It is likely that a Ru(VI) diester (4) is involved such a species was isolated and both H and NMR data suggest the structure shown in (Fig. 3.8). An X-ray crystal structure determination was carried out on the osmium analogue of (4) [178]. 

In neutral medium, and in the presence of air and cupric acetate, the ketol group is first oxidized into a ketoaldehyde that then condenses with o-phenylenediamine to produce a quinoxaline derivative. This derivative absorbs strongly in the near-UV range [82], with all of the corticosteroids affording equivalent sensitivity levels [72]. 

A silyl group directs ring expansion of a ketoaldehyde [209] via interaction with the incipent cation. 

In contrast to the preceding reagents, oxidation with H202 catalyzed by molybdate and tungstate salts or Hg(OAc)2,722,723 and the Hg(OAc)2-promoted oxidation with a molybdenum peroxo complex724 can be applied to transform acetylene and terminal acetylenes to glyoxal and a-ketoaldehydes, respectively, in fair to good yields. 

---