Formation of pyrimido[1,2-a]benzimidazoles in reaction of 1,2-diaminobenzimidazole with chalcones
The cyclocondensation of 2-aminobenzimidazole with 1,3-diketones is a known method for the synthesis of 2,4-disubstituted pyrimido[l,2-a]benzimidazoles [I]. We found that 2,4diaryl-substituted derivatives of this bicyclic compound I-III are formed by boiling solutions of 1,2-diaminobenzimidazole and 1,3-diarylpropenones in DMFA for 8 h. The reaction is accompanied by elimination of an amino group from the diamine in the 1-position in the form of ammonia: