Synthesis of novel quinoxalines by ring transformation of 3‐quinoxalinyl‐l,5‐benzodiazepine

Ring transformation of the 3‐quinoxalinyl‐l,5‐benzodiazepine ( 2 ) gave 3‐(benzimidazol‐2‐ylmethylene)‐2‐oxo‐l,2,3,4‐tetrahydroquinoxaline hydrochloride ( 4a ), whose treatment with 5% sodium hydroxide provided the free base 5a , while refluxing of the 3′‐chloro‐l‐formyl derivative 3 in acetic acid and in 10% hydrochloric acid/acetic acid afforded 3‐(3‐oxo‐3,4‐dihydroquinoxalin‐2‐yl)‐1,2‐dihydro‐1‐formyl‐2‐oxo‐3H‐1,5‐benzodiazepine hydrochloride ( 7 ) and 3‐methyl‐2‐oxo‐l,2‐dihydroquinoxaline ( 6 ), respectively. Compounds 4a and 5a were converted into 3‐(α‐hydroxyiminobenzimidazol‐2‐ylmethyl)‐2‐oxo‐l,2‐dihydroquinoxaline ( 8 ) and 3‐(benzimidazol‐2‐ylcarbonyl)‐2‐oxo‐l,2‐dihydroquinoxaline ( 10 ), respectively, which were further transformed into 3‐(benzimidazol‐2‐yl)isoxazolo[4,5‐ b ]quinoxaline ( 9 ) and 12 ‐(benzimidazol‐2‐yl)‐ 6H ‐quinoxalino[2,3‐ b I 1,5]benzodiazepine ( 11 ), respectively.