A two-step method was adopted to produce furfural from the selective dissolution and conversion of hemicellulose in pubescens. First, in GVL­(γ-valerolactone)-H2O co-solvent at 160 °C, H2O promoted the cleavage of chemical bonds linking hemicellulose, lignin, and cellulose, and GVL further helped the co-dissolution of hemicellulose (93.6 wt %) and lignin derivatives (80.2 wt %), leaving a high purity cellulose (83.3 wt %). Heating to 200 °C, the liquid system obtained with NaCl and THF added, achieved the maximum yield of 76.9 mol % with 82.2% selectivity to furfural based on the moles of converted hemicellulose using a 5 wt % pubescens to solvent ratio. It was demonstrated that NaCl with GVL promoted the depolymerization of oligomers to small molecular products (Mw < 150 Da), while the co-contribution of NaCl and co-solvent improved the selectivity to furfural. Cl– could interact strongly with C-OH-2,3,4 of the xylose unit, and the dehydration of xylose to form furfural might first occur on C-OH-4 of xylose, then on C-OH-2,3 of xylose, which enhanced the dehydration and ring open reaction via the cleavage of C1–O6 bonds, then promoted the formation of furfural by inhibiting the retro-aldol reaction to form lactic acid. The co-contribution of NaCl and co-solvent was benefical not only for the selective conversion of the mixture containing hemicellulose-derived monomers and oligomers to furfural but also for obtaining a lower molecular weight lignin derivatives (150–500 Da) that could be further used.

Solvent-thermal conversion of biomass was promising for obtaining value-added chemicals. However, little was known about the interactions between solvents and biomass in the process, which hindered the effective utilization of biomass. The effects of γ-valerolactone (GVL) and HO on enhancing pubescens degradation via the cleavage of inter- and intramolecular linkages were studied. At 160 °C, HO selectively promoted the cleavage of the intermolecular linkages by forming hydrogen bonds, making mainly contributions to hemicellulose dissolution, while GVL and HO promoted lignin dissolution by forming hydrogen bonds with -OCH group of lignin. HO promoted the cleavage of β-(1,4)-glycosidic bonds in hemicellulose derived oligomers to xylose, while the oxygen in the ring of GVL might interact with hydroxyl groups of xylose unit to enhance the dehydration of xylose to furfural, whereas GVL with HO promoted the depolymerization of lignin to oligomers mainly including β-O-4' and β-β' linkages connecting to G and S units.

The mechanism and selectivity of the asymmetric Friedel-Crafts (F-C) alkylation reaction between indole and chalcone catalyzed by chiral N, N'-dioxide-Sc(III) complexes were investigated at the M06/6-311+G(d,p)//M06/[LANL2DZ,6-31G(d)](SMD,CHCl) level. The reaction occurred via a three-step mechanism: (i) the C-C bond formation by interacting the most mucleophilic C center of indole with the most electrophilic C center of chalcone; (ii) the abstraction of the proton at the C atom of indole by counterion OTf; (iii) proton transfer from HOTf to the C atom of chalcone, generating the F-C alkylation product. The reaction preferred to occur along the favorable re-face attack pathway, producing the dominant R-product. The turnover frequency (TOF) of catalysis was predicted to be 1.59 × 10 s, with a rate constant of K( T) = 1.58 × 10 exp(-29057/ RT) dm·mol·s over the temperature range of 248-368 K. Activation strain model (ASM) and energy decomposition analysis (EDA), as well as noncovalent interaction (NCI) analysis, for the stereocontrolling transition state revealed that the substituent attached to the N atom of the amide subunits as well as the amino acid backbone of ligand played important roles in chiral inductivity. The benzyl group with structural flexibility tended to form strong π-π stacking with substrate as well as the terminal phenyl group of chalcone, stabilizing re-face attack transition state.

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Variation of the linkage or chiral backbone of an N,N′-dioxide ligand adjusts the blocking effect of ortho-iPr on the reaction site, affecting the enantiodifferentiation of two competing pathways.