2.5- Dicyano-3,6-diphenylpyrazine

The self-condensation of the bisulfite addition compound of an a-oximinoketone followed by reaction with potassium cyanide and hydrochloric acid yields 3,6-dicyano-2,5-dialkylpyrazines or, in the case of oximinoacetophenone, a mixture of 3-cyano-2,5-diphenyl-pyrazine and 3,6-dicyano-2,5-diphenylpyrazines.227... 

Gastaldi (286) first described this synthesis, in which an a-hydroxyimino ketone was treated with aqueous sodium bisulfite saturated with sulfur dioxide, and the bisulfite compound treated with potassium cyanide followed by hydrolysis with hydrochloric acid. By this procedure, Gastaldi prepared 2,5-dicyano-3,6-dimethyl-pyrazine from hydroxyiminoacetone, and 2,5-dicyano-3,6-diphenylpyrazine and some 3-cyano-2,5-diphenylpyrazine from hydroxyiminoacetophenone. He proposed a reaction mechanism involving the intermediate compounds (21) and (22). Sharp and Spring (287) used the same procedure to prepare 2,5-dicyano-3,6-diethyl-pyrazine from ethyl hydroxyiminomethyl ketone. 

Some chlorinations have been reported with thionyl chloride. 23-Dicyano-5,6-dihydroxypyrazine refluxed with thionyl chloride in pyridine was reported to give 23-dichloro-5,6-dicyanopyrazine (862) and 2-hydroxy-3-nitro-5,6-diphenyl-pyrazine with thionyl chloride gave 2-chloro-3-hydroxy-5,6-diphenylpyrazine (817, 841) but with thionyl chloride and pyridine it gave the betaine of 2-hydroxy-5,6-diphenyl-3-pyridiniopyrazine chloride (5) (863), which was hydrolyzed in acid to 2,3-dihydroxy-5,6-diphenylpyrazine (863). No product could be isolated from 2-methylpyrazine when refluxed with thionyl chloride (864). 1,4-Dimethylpiperazine-... 

Alkaline hydrolysis of 2,5-dicyano-3,6-diphenylpyrazine gave 2-carboxy-5-hydroxy-3,6-diphenylpyrazine, and analogous reactions were observed with the... 

Dicyanopyrazine with sodium methoxide in methanol with ammonia at reflux gave 5,7-diimino-6//-pyrrolo[3,4-i)]pyrazine (65) (1442) and 2,3-dicyano-5,6-dimethyl(and 5,6-diphenyl)pyrazine with hydrazine by the procedure of Patel and Castle (1339) gave 2,3-dimethyl(and 2,3-diphenyl)-5,8-diaminopyrazino[2,3-rfJ-pyridazine(s) (66) (1435). Fusion of 2-chloro-3-cyano-5,6-diphenylpyrazine with urea and thiourea was reported to give 4-amino-2-hydroxy(and mercapto)-6,7-diphenylpteridine (848). 

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