Synthesis of novel Biginelli and Hantzsch products from biorenewable furfurals using 1,4‐diazabicyclo[2.2.2]octanium diacetate as a Brønsted acidic ionic liquid catalyst

Abstract

Abstract3,4‐Dihydropyrimidin‐2(1H)‐ones (DHPMs) and 1,4‐dihydropyridines (DHPs) are well‐established classes of heterocyclic compounds with remarkable biological properties. Various protonated organic amines were screened as Brønsted acidic ionic liquid catalysts under the Biginelli and Hantzsch reaction conditions for synthesizing novel DHPMs and DHPs, respectively, starting from biorenewable furfurals. 1,4‐Diazabicyclo[2.2.2]octanium diacetate (DABCO‐DA) was found as an efficient catalyst for the organic solvent‐free synthesis of novel DHPMs and DHPs in excellent (>85 %) isolated yields. The process parameters (e. g., temperature, molar ratio of reagents, duration, and loading of acid catalyst) were optimized, and a general synthetic protocol for synthesizing DHPMs and DHPs from 5‐substituted‐2‐furaldehydes has been developed. The DABCO‐DA catalyst was successfully recovered from the reaction mixture and reused for four consecutive cycles.