Metal-Free Assemblage of Four C-N and Two C-C Bonds via a Cascade Five Component Diastereoselective Synthesis of Pyrido[1,2-a]Pyrimidines

An efficient heteroannulation synthesis of N-fused, pyrido[1,2-a]pyrimidines was successfully achieved via a sequential, one-pot five-component reaction, involving primary amines, diketene (DK), differently substituted aromatic aldehydes, nitro ketene dithioacetal and propanediamine in ethanol at 70 degrees C. This new protocol constructs two rings through the formation of four C-N and two C-C bonds via a one pot sequential reaction involving ring-opening/ Knoevenagel condensation, /nucleophilic substitution (SN)/ Michael addition followed by imine-enamine tautomerization and final N-heterocyclization. The method is particularly attractive due to the advantages such as: atom economy, optimum convergence, commercially available or readily accessible starting materials, high bond-forming efficiency, free metal-catalyst and mild reaction conditions. The products were isolated by just decantation of the solvent and purification without using column chromatography method.