Reaction of 1,3-diaryl-2-propene-1-ones with o-Phenylenediamine

ABSTRACT

The propenones [1a-f] react with o-phenylenediamine in solution to give mainly 2,4-diaryl-2,3-dihydro-1 H-1,5-diazepines [3a-f], respectively, whereas, the analogous propenones [1g-i] afford 2- arylbenzimidazoles. The effect of base catalysis was discussed. The diazepines were also obtained when the components reacted at 120C without a solvent, whereas, at higher temperature 2-arylbenzimidazoles were mainly obtained. Thermolysis of the dihydrodiazepenes afforded 2-arylbenzimidazoles retaining the 4-phenyl ring of the diazepine as the major product together, in some cases, with 2-arylbenzimidazole retaining the 2-substituent