Phenylglyoxal

Oxidation of acetophenone with selenium dioxide in the presence of dioxan or ethyl alcohol as solvent affords phenylglyoxal  

C6HsCOCH3 + Se02 — C,H6COCHO + Se + H20 This is one example of the oxidation by selenium dioxide of compounds containing a methylene group adjacent to a carbonyl group to the corresponding a-ketoaldehyde or a-diketone (see also Section VII,23). 

In a i-l. three-necked, round-bottomed flask fitted with a liquid-sealed stirrer and a reflux condenser are placed 600 cc. of dioxane (Note 1), in g. (1 mole) of selenium dioxide (Note 2), and 20 cc. of water (Note 3). The mixture is heated to 50-55° and stirred until the solid has gone into solution, 120 g. (1 mole) of acetophenone is added in one lot, and the resulting mixture is refluxed with continued stirring for four hours (Note 4). The hot solution is decanted from the precipitated selenium, and the dioxane and water are removed by distillation through a short column. The phenylglyoxal is distilled at diminished pressure from a 250-cc. Claisen flask (Note 5), and the fraction boiling at 95-97V25 mm. collected (Note 6). The yield is 93-96 g. (69-72 per cent of the theoretical amount) (Note 7). 

The aldehyde sets to a stiff gel on standing, probably as the result of polymerization. It may be recovered without appreciable loss by distillation. Phenylglyoxal may be preserved also in the form of the hydrate, which is conveniently prepared by dissolving the yellow liquid in 3.3-4 volumes of hot water and allowing crystallization to take place (Note 8). 

Ethyl alcohol (95 per cent) can also be used as solvent. The reaction can be carried out with an excess of acetophenone 

Commercial selenious acid (129 g., 1 mole) may be used in place of the mixture of selenium dioxide and water. 

After about two hours the solution becomes clear and little further precipitation of selenium is observable. 

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Reaction of (25,55)- and (2i ,55)-2-[5-(terc-butyldimethylsilyloxy)piper-idin-2-yl]ethanols with phenylglyoxal monohydrate in the presence of 4 A molecular sieves in boiling CH2CI2 overnight gave (15,4n5,7i )- and (2i ,4ni ,7i )-l-benzoyl-7-(terc-butyldimethylsilyloxy)perhydropyrido[l,2-c][l,3]oxazines 97 and 100, respectively, in good yield (99MI19). Both products were accompanied by unidentified minor isomers. 

Another chiral auxiliary used in diastereoselective addition reactions is the 1,3-oxazine derivative 4a which shows a close structural resemblance to the 1,3-oxathiane 16 (vide supra). However, in contrast to the oxathiane, 4a cannot be readily acylatcd in the 2-position. Therefore, the benzoyl derivative 4b was prepared by condensing amino alcohol 3 with phenylglyoxal. 

Benzoin (Coll. Vol. 1, 88) From phenylglyoxal and benzene in the presence of aluminum chloride, in 90 per cent yield. Arnold and Fuson, J. Am. Chem. Soc. 58, 1295 (1936). 

Iminium ions bearing an electron-withdrawing group bonded to the sp carbon of the iminium function are very reactive dienophiles. Thus, iminium ions 26 generated from phenylglyoxal (Scheme 6.15, R = Ph) or pyruvic aldehyde (R = Me) with methylamine hydrochloride, react with cyclopenta-diene in water at room temperature with good diastereoselectivity [25] (Scheme 6.15). If glyoxylic acid is used, the formation of iminium salt requires the free amine rather than the amine hydrochloride. 

Nitro-l,2-benzenediamine (165) and l-methyl-2-phenylglyoxal (166) gave a mixture of 2-methyl-7-nitro- (167) and 2-methyl-6-nitro-3-phenylquinoxaline (168) (MeOH, reflux, min >70%), subsequently separated chromatogra-... 

Biphenyltetramine and l-(perfluoroheptyl)-2-phenylglyoxal gave a product formulated as 3,3 -bis(perfluoroheptyl)-2,2 -diphenyl-6,6 -biquinoxaline (169) (m-cresol, 20°C, 24 h 92% possibly containing both other possible... 

Benzenediamine (182) and l-methyl-2-phenylglyoxal 2-oxime (183a) or the isomeric 1-oxime (183b) gave 2-methyl-3-phenylquinoxaline (184) (EtOH, reflux, 90 min 80% or 90%, respectively)homologs likewise. ° ... 

Diastereomerically pure 1,3-dioxanes are formed when optically pure l-aryl-2,2-dimethylpropan-l,3-diols react with phenylglyoxals only ketalisation is observed <96RTC407>. 

Reaction of aldehydes and ketones with methanol or glycols at ambient temperature in the presence of excess trimethylchlorosilane (TCS) 14 to form acetals, hexamethyldisiloxane 7, and HCl is achieved very simply [28]. Thus cyclohexanone and diacetyl react with free glycol and TCS 14 to give the acetals 392 and 405 in 95% yield [28]. Reaction of phenylglyoxal with methanol in the presence of trimethylchlorosilane 14 affords the acetal 406 in 83% yield [28], whereas catechol 79 is converted by pivaldehyde into acetal 407 in 91% yield [29] (Scheme 5.5). 

The pyruvaldehyde and phenylglyoxal adducts (19) with trimethyl phosphite reacted with isocyanates to give the carbamoyl-1,3,2-dioxa-phospholens (20), probably as shown. These, with hydrogen chloride, gave phosphate esters of )3-keto-a-hydroxyamides. 

Zinc complexes of cyclohexane-1,2-dione bis(thiosemicarbazone) have been formed in the neutral and doubly deprotonated form. The X-ray structures show distorted square-based pyramidal geometries for both complexes [ZnL(OH2)] and [Zn(H2L)Cl]Cl with the water or chloride occupying the axial position.886 The binuclear complex bis[l-phenylglyoxal bis(3-piperidylthiose-micarbazone)zinc] was synthesized by electrochemical methods and reveals a Zn2L2 with two tetradentate bis-thiosemicarbazone ligands bridging the metal centers.887... 

The reaction of dicarbonyl compounds, such as glyoxal or phenylglyoxal, with a guanidinyl group, such as that of an arginine residue, proceeds to yield a more stable linkage due to the formation of a cyclic derivative (Reaction 46). 

Takahashi, K. (1968) The reaction of phenylglyoxal with arginine residues in proteins. J. Biol. Chem. 243, 6171-6179. 

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