A new one-pot Bischler–Napeiralski type cyclization reaction between pyridine-1,2-diamines and various carboxylic acids with PPA as catalyst to prepare pyridobenzodiazepines is proposed. In the new synthetic route, the reaction time is only one-third of the methods reported. The synthetic strategy provides an efficient way to prepare novel structurally diversified heterocyclic compounds of pyridobenzodiazepine family with potential pharmaceutical or biological activities.