Cascade Reactions Involving Aromatic N-Heterocycles: C-N Bond Formation as Key-step Towards the Synthesis of N-fused Polycyclic Heterocycles

Background: Polyheterocyclic compounds have numerous applications in different fields ranging from medicinal chemistry to material science. Cascade reactions represent the most direct and efficient method to obtain polyheterocyclic molecules with functional diversity and increased complexity. Moreover, novel polycyclic systems can be generated which can possess interesting properties such as biological activity or luminescence. The number of polyheterocyclic compounds obtained through cascade reactions, including multi-component reactions, is wide and this review will be limited to polyheterocycles obtained from aromatic N-heterocycles: pyrrole, pyrazole, triazole, pyridine, pyrimidine, indole, benzimidazole, quinoline and other mono- or bicyclic compounds. Objective: The review will cover the period ranging from 2006 to 2015 and will focus on processes involving the formation of C-N bonds with the heterocyclic nitrogen.