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
Graphical Abstract
In present work, a new class of pyrido[1,2-a]pyrimidines is easily prepared by one-pot five-component approach incorporating a domino ring-opening/ Knoevenagel condensation, /nucleophilic substitution (SN)/ Michael addition followed by imine−enamine tautomerization and final N-cyclization reaction sequence. The merit of this sequential reaction is highlighted by its high atom-economy, excellent yields, unusually high multiple bond-forming efficiency, excellent functionality tolerance, use of readily available commercial reagents and operationally simple synthetic protocols.
Abstract
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 °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.
Conflict of interest
The authors declare no conflict of interest.