SiO2/H2SO4: An Efficient Catalytic System for Solvent-free 1, 5-benzodiazepines Synthesis

1, 5-Benzodiazepines have been investigated extensively by organic chemists due to their medicinal and pharmacological properties. These compounds are synthesized by condensation of o-phenylenediamines with carbonyl compounds in the presence of acid catalysts. During our studies on the application of silica resin with acid functional moieties, we found that SiO2/H2SO4 mixture is a simple and efficient catalyst for this method under microwave irradiation. The reaction was carried out simply by grinding SiO2/H2SO4 mixture with o-phenylenediamine, and ketone in the mortar; then the mixture was poured out into a sealed flask. Subsequently, it was irradiated in a microwave oven. In this method a series of cyclic and acyclic ketones underwent above conversion to form corresponding 1, 5-benzodiazepines. In conclusion, this method is a simple, rapid, and high yielding reaction (78–95%).