Silica gel/NaHSO4:: An efficient and recyclable heterogeneous catalyst for high yield synthesis of 1,5-benzodiazepine derivatives under microwave irradiation

Silica gel supported sodium hydrogen sulfate catalyzes efficiently the condensation of o-phenylenediamines with ketones under microwaves in solvent free conditions to afford the corresponding 1,5-benzodiazepine derivatives in high yields. Compared to conventional reaction conditions, this new approach consistently has the advantage of excellent yields (90-98%) and short reaction times of 0.50 - 1.00 min.