Phosphazene superbase mediated cyclization and annulation reactions of functionalized alkynes for the synthesis of heterocyclic compounds

Base-mediated cyclization and annulation reactions are very useful methods in the heterocyclic synthesis. Different types of conventional bases, i.e . , inorganic bases or organometallic bases have been traditionally used for carrying out these reactions in the past. Over the years, the phosphazene organic superbases have emerged as effective alternatives to inorganic and organometallic bases. The phosphazene superbase was first used for alkyne cyclization in 2008, and its use has become quite popular over the last decade. This review is aimed to provide an analysis of the use of phosphazene superbase, especially P 4 – t -Bu as a robust and highly efficient catalyst/reagent in various intra- or intermolecular reactions of substituted alkynes for the synthesis of O,N-heterocycles such as isoindolin-1-ones, benzofurans, isobenzofurans, proline derivatives, pyrroles, etc.