Access to a Novel Class of Tetracyclic 1,4-Benzodiazepin-5-ones Starting from a-Amino Acids by Pd-Catalyzed Amination/1,3-Dipolar Cycloaddition as the Key Steps

A convenient procedure for the preparation of the novel class of tetracyclic imidazo[2,1-c]pyrazolo[1,5-α][1,4]benzodiazepine-5,8-diones is reported. The protocol uses cheap and easily accessible α-amino acids as chiral-pool starting materials and leads to products in an enantiopure form. An intramolecular palladium-catalyzed amination process to form the imidazole nucleus and an intramolecular 1,3-dipolar cycloaddition reaction to simultaneously achieve the pyrazole and 1,4-diazepine rings are the key steps.