Of benzoin with urea

The condensation of benzoin with urea to produce 4,5-diphenylglyoxalone is carried out by refluxing the reactants in acetic acid. ... 

The reaction of urea (and thiourea) derivatives with a-hydroxy-ketones yields imidazoles. Thus, condensation of benzoin with N-pheny 1 thiou rea in hexanol in the presence of catalytic quantities of HC1 (or dry HC1) gives l,4,5-triphenylimidazole-2-thione (21) in 50-60% yield.100... 

Infrared spectral data have been advanced to support the oxo formulation for 96 (R —propyl). Structure 96 (R= phenyl) has also been proposed on the basis of the fact that benzoin does not condense with urea, and this conclusion is probably correct, although the argument is not convincing. The oxo forms of benzimidazolone, 97 106,10- related pyrazinoimidazolone 98 have been shown... 

Diarylquinoxalines are similarly prepared by reaction of o-phenylenediamine with benzils. The required benzils have been prepared traditionally by oxidation of the corresponding benzoins, which in turn have been prepared by treatment of the appropriate aldehydes with potassium cyanide. In a more recent procedure, benzils have been obtained in good yield by oxidation of para-substituted diphenyloxazoles with bromine in acetic acid. The oxazoles themselves are readily prepared by cyclization of the benzoin acetate with urea (Scheme 3). ... 

It is prepared by the eondensation of two moleeules of benzaldehyde with sodium cyanide to get benzoin, which on treatment with nitric acid or cupric sulphate forms benzil. In the presence of sodium ethoxide, benzil in hot condition yields benzilic acid ester, (a) The latter on condensation with urea in the presence of sodium ethoxide give rise to phenytoin the enol-form of which on neutralization with sodium hydroxide ultimately results into the formation of phenytoin sodium. 

Alternatively, the oxidation may occur by coupling to a suitable reactant. In 1997, Miyashita explored the scope of oxidative aroylations with nitrobenzene (Scheme ll.lO)." With the same oxidative reagent, nitrobenzene, benzoin reactions had already been developed back in 1982 using cyanide or thiamine. The combination of an aldehyde and nitrosobenzene, in the presence of an NHC, led to the formation of 7V-phenyl hydroxamic acids in good yields. These can be further converted into hydroxamic esters via a one pot reaction in the presence of a second (o,p-unsaturated) aldehyde. Furthermore, the oxidative coupling of aldehydes with carbodiimides in air allowed access to Af-acyl urea derivatives with IMes HCl 19 as the NHC precursor. Related thioesterifications reactions have also been reported using... 

Whereas condensation of a-hydroxy ketones such as benzoin and acetoin on heating with formamide [240] or ureas in acetic acid [239, 242] to form imidazoles such as 769 or 770 is a well known reaction, only two publications have yet discussed the amination of silylated enediols, prepared by Riihlmann-acyloin condensation of diesters [241], by sodium, in toluene, in the presence of TCS 14 [241, 242]. Thus the silylated acyloins 771 and higher homologues, derived from Riihl-... 

When urea (or thiourea) reacts with a-hydroxy ketones or a-diketones the products are imidazolin-2-ones (or -thiones) (70AHC(12)103,66RCR122). The reaction is limited to the preparation of 4,5-alkyl(or aryl)- or l,4,5-trialkyl(or triaryl)-imidazoles since an oxygen or sulfur function appears at C-2. Benzoin condenses with iV-phenylthiourea in hexanol in the presence of catalytic quantities of HCl to give l,4,5-triphenylimidazoline-2-thione (131) in 50-60% yield (Scheme 69). While 1-methylurea can also take part in the reaction. 

Benzoin, tetraphenylethanediol, hydrazobenzene and 1,2-diphenyl-1,2-ethanedione bishydrazone are oxidized by methyl bis(l-naphthyl)bismuthi-nate to benzil, benzophenone, azobenzene and diphenylacetylene, respectively [88CL2021] (Section 5.2.4). Amides, thioamides, ureas and thioureas are A-acylated in good yield with acetic acid in the presence of the bismuthi-nate at room temperature [90CL1651] (Scheme 3.11). 

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