Dicyanopyrazine studies. Part V: Syntheses and characteristics of chalcone analogues of dicyanopyrazine

Chalcone analogues based on 2,3-dicyanopyrazine were synthesized by the condensation reaction of 2-acetyl-3-methyl-5,6-dicyanopyrazine 4a with various arylaldehydes. Oxidation of pentane-2,4-dione with selenium dioxide gave pentane-2,3,4-trione, which reacts with diaminomaleonitrile to give 4a. These chalcolone dyes showed solvatochromism depending on the polarity of the solvents, but the chromophoric system was interupted at the carbonyl group by steric requirements of substituents. The seven membered azepine, obtained from diaminomaleonitrile and a 1,3-dicarbonyl compound, was further reacted with an arylaldehyde to give a new fluorescent heterocycle. Optimization of the chemical structure of the products was evaluated by the MOPAC PM 3 method and was correlated with their spectral properties. (C) 1998 Elsevier Science Ltd. All rights reserved.