DFT study on the CuBr-catalyzed synthesis of highly substituted furans: effects of solvent DMF, substrate MeOH, trace H2O and the metallic valence state of Cu

Abstract

The CuBr-catalyzed 2-(1-alkynyl)-2-alken-1-ones are selected as a research system to explore the effects of solvent DMF, substrate MeOH, trace H₂O and the valence state of Cu on the synthesis of highly substituted furans using the BHandHLYP density functional. Our calculations suggest that DMF, MeOH and H₂O can be used as hydrogen-bond acceptors to accelerate intermolecular nucleophilic addition. More importantly, they play the role of proton shuttles to assist H migration significantly by reducing the free energy barrier of the H-transfer process. Due to the participation of DMF, MeOH or H₂O, the rate-determining step is changed from the H-transfer process (96.0 kJ mol⁻¹) to the intramolecular cyclization step (57.6 kJ mol⁻¹). In addition, calculated results also show that the yield can be further improved when CuBr is replaced by CuBr₂. In short, the present study can provide insight into the metal-catalyzed reactions involving H-transfer processes and can act as a guideline for the design of new catalysts for metal-catalyzed reaction applications.