Preparation of stable 1,4-dihydropyrazines

Abstract

The N-phenacylarylamine (4) gives the N,N-diphenacyl derivative (5) on treatment with phenacyl bromide under phase-transfer catalysis conditions. Condensation of (5) with an arylamine results in the formation of the thermally stable 1,4-diaryl-3,5-diphenyl-1,4-dihydropyrazine (6) in moderate yield. 1,2-Diaryl-3,6-diphenyl-1,2-dihydropyrazine (9) is obtained by heating N-phenacylarylamine (4). Formation of (9) is also promoted by a Lewis acid at lower temperature.