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

3,4-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 Bronsted 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.

Automated summary

Various protonated organic amines were screened as catalysts for the synthesis of DHPMs and DHPs starting from furfurals. 1,4-Diazabicyclo[2.2.2]octanium diacetate (DABCO-DA) was found to be an efficient catalyst, leading to high yields (>85%) in an organic solvent-free reaction. The process parameters were optimized, and a general synthetic protocol was developed. The DABCO-DA catalyst could be recovered and reused for multiple cycles.