Benzil quinoxaline

This rapid formation of the crystalline quinoxaline derivative can therefore be used to identify 1,2-diketones conversely, a nuclear-substituted o-phenyl-enediamine can be identified by the quinoxaline derivative which it forms with a known 1,2-diketone such as benzil. 

Ortho quinones (and also aromatic a-diketones, e.g., benzil) react with o-phenylenediamine to yield quinoxalines as follows. Dissolve the substance... 

Methoxy-5,6-quinoxalinediamine (191) and glyoxal gave 5-methoxypyrazino [2,3-/]quinoxaline (192) (EtOH, H20, reflux, 1 h >70%) 195 2,3-di-phenyl-5,6-quinoxalinediamine and benzil likewise gave 2,3,8,9-tetraphenylpyra-zino[2,3-/]quinoxaline (193) (AcOH, reflux, 1 h %).955... 

Reduction of 2-amino-3-nitrodibenzothiophene in the presence of acetic acid yields the imidazole (109) and by conducting this reaction in the absence of acetic acid 2,3-diaminodibenzothiophene should be readily accessible. A similar reduction of 3-amino-4-nitrodibenzothio-phene yields 3,4-diaminodibenzothiophene (60%). In addition to the typical reactions described above for the 1,2-diamino compound, 3,4-diaminodibenzothiophene condenses with benzil to give the quinoxaline... 

The preparation of quinoxaline derivatives carrying a substituent in the benzene ring requires suitably substituted o-phenylenediamines. These have been prepared by reductive cleavage (SnCl2) of appropriately substituted 2,1,3-benzoselenadiazoles (I9).21 Benzo-selenadiazoles, readily prepared from 1,2-diaminobenzenes and selenium dioxide, undergo halogenation at positions 4 and 7 and sulfonation at C-4. 5,6-Dichloro- 2,3-diphenylquinoxaline has been synthesized from benzil and l,2-diamino-3,4-dichlorobenzene, the diamine in turn was obtained from 4,5-dichloro-2,l,3-benzoselenadiazole.22... 

Side chain quinoxaline functionalization has been achieved (77NKK556) by reaction of o-phenylenediamine (249) with benzil-functional polymers. Thus, reaction with polyamide... 

Benzils, like other 1,2-diones, react with 1,2-benzenediamines to form diaza-arenes known as quinoxalines. This kind of reaction is an important general procedure for the synthesis of aromatic ring systems containing nitrogen ... 

Exercise 26-33 Write a mechanism based on analogy for the formation of quinoxalines from benzils and 1,2-benzenediamines. (Review Section 16-4C.)... 

Keywords o-phenylendiamine, benzil, cyclization, cascade reaction, melt reaction, waste-free, solid-solid reaction, quinoxaline... 

Cognate preparations. 2,3-Diphenylquinoxaline. To a warm solution of 2.1 g (0.01 mol) of benzil in 8 ml of rectified spirit add a solution of 1.1 g (0.01 mol) of o-phenylenediamine in 8 ml of rectified spirit. Warm in a water bath for 30 minutes, add water until a slight cloudiness persists and allow to cool. Filter and recrystallise from aqueous ethanol to give 1.43 g (51%) of 2,3-diphenyl-quinoxaline, m.p. 125-126 °C. 

Amino-6-nitro-Fischer s base (36, R = N02) was reduced to the 5,6-diamino compound (36, R = NH2) in 80% yield, which (as its hexachlorostannate salt) was condensed with benzoic acid and with benzil to give, respectively, a 68% yield of 5,7,7-trimethyl-6-methylene-6,7-dihydro-5 7/-pyrrolo[2,3-/]-benzimidazole (37) and a 62% yield of 6,8,8-trimethyl-7-methylene-2,3-diphenyl-7,8-dihydro-6 7/-pyrrolo[2,3-g]quinoxaline (38).42 Spiropyrans from these linearly annellated Fischer s bases were not reported they likely would color upon irradiation with blue light. 

The reaction between aromatic 1,2-diamines and 1,2-diketones affords 2,3-disubstituted quinoxaline derivatives (see table below) " however, a number of hindered a-ketones fail to react. " Unsymmetrical diketones give mixtures of isomers whose ratio varies with the acidity of the medium in some examples. A mechanistic study of quinoxaline formation from benzene-1,2-diamine and benzil has been described." ... 

Weigh 0.20 g of benzil (theory = 210 mg) and 0.10 g of your purified o-phenylenediamine (theory = 108 mg) into a 20 x 150-mm test tube and heat in a steam bath for 10 min, which changes the initially molten mixture to a light tan solid. Dissolve the solid in hot methanol (about 5 mL) and let the solution stand undisturbed. If crystallization does not occur within 10 min, reheat the solution and dilute it with a little water to the point of saturation. The crystals should be filtered as soon as formed, for brown oxidation products accumulate on standing. The quinoxaline forms colorless needles, mp 125-126°C yield is 185 mg. 

Fourth, benzils also play an important role in phytochemicals. Some of benzils could be the inhibitors of the acid corrosion of steel, as well as used in the photocurable coatings. However, benzils of benzil (21) (Figure 6) could also be used as the intermediates in their synthesis of diverse heterocycles sueh as imidazoles of imidazole (22) (Figure 6) or quinoxalines of quinoxaline (23) (Figure 6) [44]. 

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