TThe polycyclic benzo-imidazo-pyrrolone system is present in chemical entities with very relevant pharmacological properties. One of the most efficient synthetic methods to access this system involve the gold(I)-catalyzed reaction of alkynes bearing tethered carboxylic groups with 1,2-diaminobenzene. However, the high cost is one of drawbacks of this method. In this context, we report here the development of a simple and efficient metal-free synthetic method to access the benzo-imidazo pyrrolone system. The methodology developed is based on the reaction of secondary β-enamino diketones with o-phenylenediamine through in situ generated of the key intermediate 4-acyl-3,5 dihydroxypyrrolone.