2.3- Diphenyl-5,6-dihydropyrazine oxidation

JV-benzoyl- and jV.V -dibenzoylethylenediamine, 2-phenylimidazo-line, and benzoic acid. The formation of these products is rationalized by mechanisms involving the initial addition of hydrogen peroxide to the dihydropyrazine to give the hydroperoxide. It appears therefore that the earlier report386 that peracetic acid oxidation of 5,6-diphenyl-2,3-dihydropyrazine gives the 1,4-di-iV-oxide is incorrect.386 ... 

It has been claimed (25) that 2,3-diphenyl-5,6-dihydropyrazine when heated with acetic or benzoic anhydride gives a derivative of the 1,4-dihydropyrazine ring system, but this has been shown by Chen and Fowler (1562) to be in error [the products have been shown to be 1,4-diacetyl(or dibenzoyl)-5,6-diphenyl-l,2,3,4-tetrahydropyrazine (26, R = Me or Ph), respectively, together with 23-diphenyl-pyrazine]. Hexamethyl-2,3-dihydropyrazine cannot undergo oxidation to a pyrazine, but it rapidly dimerized in air in the presence of hydrochloric acid to give compound (27, X = Cl) (also prepared as the iodide with iodine in ether) (1550). 

Hydrolysis of l,4-diacetyl-2,3-diphenyl-l,4-dihydropyrazine with potassium hydroxide in ethylene glycol produced 2,3-diphenylpyrazine (probably formed by air oxidation of the dihydropyrazine) (1562). l,4-Dimethyl-2,6-diphenyl-l,4-dihydropyrazine reacts with methanol to give 2-methoxy-1,4-dimethyl-3,5-diphenyl-1,2,3,4-tetrahydropyrazine (57) (1536). 

The reactions of 2,5-dimethyl-3,6-diphenyl-2,5-dihydropyrazine 1,4-dioxide and 3,6-diphenyl-2,5-dihydropyrazine 1,4-dioxide with acetic anhydride and a small amount of sulfuric acid afforded 2,5-dimethyl-3,6-diphenylpyrazine 1-oxide and... 

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