Lanthanide One-Dimensional Coordination Polymer Catalyzed [3+2] Annulation Reaction: Synthesis of N,N’-Bicyclic Pyrazolidine Scaffolds

Abstract

Self-assembly of the multidendate ligand (H₂L) with lanthanide metal salts leads to the formation of one-dimensional coordination polymers (CP). The structural analysis of the molecule suggests the formation of CP with ladder-type arrangements of ligands with metal centers. The polymers CP-1 and CP-2 with europium and terbium were found to be anionic and coordinatively unsaturated with the existence of solvent molecules in the vacant sites. The CPs were found to be suitable catalysts for the regioselective annulation of aza-MBH adducts with N,N, cyclic azomethine imines that lead to the formation of N,N’-bicyclic pyrazolidine scaffolds via [3+2] cycloaddition. The protocol tolerates a wide substrate scope with different functionalities by producing the bicyclic scaffold with better yield and excellent diastereoselectivity. The X-ray and NMR analysis suggests the formation of cis diastereomer which is stabilized by N−H—O interaction. The synthetic utility of the pyrazolidine scaffolds is attempted for various functional group interconversions.