Zirconyl(IV) chloride: a novel and efficient reagent for the rapid synthesis of 1,5-benzodiazepines under solvent-free conditions

o-Phenylenediamines undergo rapid condensation with ketones having hydrogens at the α-position in the presence of 10 mol% zirconyl(IV) chloride under extremely mild reaction conditions to afford the corresponding 1,5-benzodiazepines in excellent yields with high selectivity. This method works well for both electron-rich as well as electron-deficient o-phenylenediamines.