Triethylammonium Hydrogen Sulfate [Et₃NH][HSO₄]-Catalyzed Rapid and Efficient Multicomponent Synthesis of Pyrido[2,3-<i>d</i>]pyrimidine and Pyrazolo[3,4-<i>b</i>]pyridine Hybrids

Abstract

An operationally simple, one-pot multicomponent reaction has been developed for the assembly of pyrido[2,3-<i>d</i>]pyrimidine and pyrazolo[3,4-<i>b</i>]pyridine derivatives (<b>4a</b>-<b>4am</b>) in excellent yields (92-94%) with high purity. The reactions were easy to perform simply by mixing of electron-rich amino heterocycles (including aminouracils and aminopyrazoles), aldehyde, and acyl acetonitrile in the presence of [Et₃NH][HSO₄] under solvent-free conditions. The remarkable feature of the present approach is that the ionic liquid possesses dual solvent-catalytic engineering capability. Results of this study revealed that 1 mmol of the ionic liquid catalyst under solvent-free conditions at 60 °C is the best reaction parameter for the construction of fused pyridine and pyrimidine derivatives in excellent yields. The present methodology showed good results under gram-scale conditions, thereby indicating its applicability in industrial as well as academic settings in the near future.