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.