2.5- Dibenzyl-3,6-diphenyl-3,6-dihydropyrazine

A similar reaction involving co-bromoacetophenone and benzylamine has been studied by Mason and Winder (26). The monophenacylbenzylamine hydrobromide (13) (from the reagents) with potassium hydroxide at 100° was claimed incorrectly to form 1,4-dibenzyl-2,5-diphenyl-l, 4-dihydropyrazine (14) (see p. 344), which gave 2,5-diphenylpyrazine. Bromopyruvic acid with aqueous ammonia and mercuric chloride at 55° gave 2,5-dicarboxypyrazine (236a). 

Mason and Winder (26) reported that the base-catalyzed cyclodehydration of JV-phenacylbenzylamine hydrobromide (1) gave 1,4-dibenzyl-2,5-diphenyl-1,4-dihydropyrazine (2) but Chen and Fowler (1535) showed that the product was l,2-dibenzyl-3,6-diphenyl-l,2-dihydropyrazine (3) (20%). Further investigation by... 

Lown and Akhtar (1536) revealed a second product from this reaction, namely l,2-dibenzyl-2,5-diphenyl-1,2-dihydropyrazine (59%) (4). Lown and Akhtar(1537) also showed that the self-condensation of A -isopropylphenacylamine at room temperature gave 1,2-diisopropyl-2,5-diphenyl-1,2-dihydropyrazine (and proposed l,4-diisopropyl-2,5-diphenyl-l,4-dihydropyrazine as an intermediate). In a similar series of reactions of A -alkylphenacylamines, the thermally induced selfcondensations were followed by regiospecific 1,3-shifts to substituted carbon atoms to give in good yields l,2-dialkyl-2,5-diphenyl-l,2-dihydropyrazines at temperatures ranging from ambient to 140° (1536). 

The reactions of A -benzyl-A, A-diphenacylamine hydrobromide with benzylamine at 120-130° was also reported to give 1,4-dibenzyl-2,6-diphenyl-l, 4-dihydropyrazine... 

Pyrolysis of 1,2-dibenzyl-3,6-diphenyl-1,2-dihydropyrazine (3) gave a mixture of 2,5-diphenylpyrazine, 3-benzyl-2,5-diphenylpyrazine, 2,5-dibenzyl-3,6-diphenyl-pyrazine, and toluene (1535), and pyrolysis of l,2-dibenzyl-3,5-diphenyl-l,2-dihydropyrazine formed a mixture of 2,6-diphenylpyrazine and 2-benzyl-3,5-diphenylpyrazine (1535). l-Benzyl-2,3,5-triphenyl-l,2-dihydropyrazine refluxed with palladium on charcoal in benzene gave 2,3,5-triphenylpyrazine (1542) and the... 

---