Electrocatalytic synthesis of heterocycles from biomass-derived furfuryl alcohols

Abstract

It is very attractive yet underexplored to synthesize heterocyclic moieties pertaining to biologically active molecules from biomass-based starting compounds. Herein, we report an electrocatalytic Achmatowicz reaction for the synthesis of hydropyranones from furfuryl alcohols, which can be readily produced from biomass-derived and industrially available furfural. Taking advantage of photo-induced polymerization of a bipyridyl ligand, we demonstrate the facile preparation of a heterogenized nickel electrocatalyst, which effectively drives the Achmatowicz reaction electrochemically. A suite of characterization techniques and density functional theory computations were performed to aid the understanding of the reaction mechanism. It is rationalized that the unsaturated coordination sphere of nickel sites in our electrocatalyst plays an important role at low applied potential, not only allowing the intimate interaction between the nickel center and furfuryl alcohol but also enabling the transfer of hydroxide from nickel to the bound furfuryl alcohol.

Fig. 1. Application and synthesis development of hydropyranones.

a Representative compounds containing hydropyranone units used in the syntheses of biologically active compounds. b Reported chemical and c electricity-assisted oxidation strategies for the Achmatowicz reaction. d Our proposed electrocatalytic Achmatowicz reaction operating in water.

Fig. 2. Illustration of catalyst preparation.

Photo-induced polymerization of dvbpy followed by metal cation incorporation to prepare M-DVBP electrocatalysts.

Fig. 3. Catalyst characterization.

a FT-IR spectra of dvbpy and DVBP. b Raman spectra of DVBP and Ni-DVBP. c, d SEM images of Ni-DVBP at different magnifications. High-resolution XPS spectra of Ni 2p e and N 1 s f.

Fig. 4. Electrochemistry study of Ni-DVBP.

a CV curve of Ni-DVBP collected in acetonitrile at a scan rate of 100 mV/s. b Scatter plot of anodic and cathodic peak currents of Ni-DVBP versus scan rate, together with linear fitting lines. c CV comparison of carbon paper, DVBP, and Ni-DVBP collected in 0.1 M KPi at pH 7.0. d CV curves of Ni-DVBP with and without 10 mM furfuryl alcohol in 0.1 M KPi at pH 7.

Fig. 5. Quantification of the electrocatalytic Achmatowicz reaction.

a Conversion of furfuryl alcohol and yields of its oxidation products over passed charge during electrolysis at 1.4 V vs Ag/AgCl in 0.1 M phosphate buffer using Ni-DVBP as the working electrode. b Conversion of furfuryl alcohol and yield of hydropyranone for four consecutive electrolysis cycles at 1.4 V vs Ag/AgCl in 0.1 M phosphate buffer utilizing the same Ni-DVBP as the working electrode.

Fig. 6. Substrate scope.

The Achmatowicz reaction yields of furfuryl alcohol derivatives obtained on Ni-DVBP at 1.4 V vs Ag/AgCl in 0.1 M phosphate buffer of pH 7. The corresponding product yields obtained from chemical oxidation using m-CPBA as the oxidant are also included for comparison. ^*Electrolysis at 1.8 V vs Ag/AgCl.

Fig. 7. Plausible reaction mechanisms.

a Mechanism 1: DFT calculated energy profile of catalytic intermediates using [(bpy)Ni(H₂O)₂]²⁺ as a catalyst model. The optimized chemical structure of each intermediate is also included. b Mechanism 2: The chemical structure of each intermediate using the same catalyst model but following the oxygen-atom transfer pathway.