LAUSR

Abstract Pyridopyrimidinones are class of heterocyclic compounds which serves as important precursors in organic transformation and medicinal chemistry. In the current work three derivatives of pyrido[1,2-a]pyrimidine-3-carboxylates (1, 2 and 3) has been synthesized and characterized by NMR. The crystal structure of compound 1 (C12H12N2O3.HCl) and 2 (2(C12H12N2O3)) were solved in monoclinic system with P21/c space group and 3 (C11H9BrN2O3) shows concomitant polymorphism and solved in orthorhombic system with Pna21 and Pca21. The weak C—H⋯O and C—H…N intermolecular interactions play significant role in crystal packing of 4-Oxo-4H-pyrido[1,2-a]pyrimidine-3-carboxylates. Replacement of methyl group in compound 1 with Bromine atom resulted 3 with increased π…π stacking interactions. The unexpected concomitant polymorphic forms of compounds 3 with details of the crystal structures and supramolecular features are presented. In addition, Hirshfeld surface and 2D fingerprint plots were performed to understand the various intermolecular non-covalent interactions in pyrido[1,2-a]pyrimidine-3-carboxylates.