Ultrasound Assisted One-Pot Synthesis of Some 1, 5-Benzodiazepine Derivatives

A successful cyclocondensation reaction using silica gel as a green catalyst and ultrasound as green reaction medium was carried out. Ten derivatives (I a-j) were synthesized of which eight 2, 2, 4-trisubstituted-2, 3-dihydro-1H-1, 5-benzodiazepine derivatives (I a-h) were prepared from variety of ketones. 2, 4-disubstituted-2, 3-dihydro-1H-1, 5- benzodiazepine (I-ia) and (I-ib) were obtained by using ethyl acetoacetate, I-ib as a minor product resulted from the enolic form of ethyl acetoacetate while indicating that the keto form of 1, 3-β-dicarbonyls led to major product formation. Intermolecular imine-enamine type of cyclization was catalyzed by silica-gel acting as a Lewis acid.