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.

The counterion and substituent on amide of the N,N′-dioxide ligand could affect electrostatic energy (ΔVelstat) as well as orbital energy (ΔEorb) between CH2O and Sc(iii)-based catalyst, adjusting the Lewis acidity of the metal centre.

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The reaction mechanism and enantioselectivity of the asymmetric [2 + 2] cycloaddition between an alkynone (R1) and a cyclic enol silyl ether (R2) were studied theoretically by the DFT method at the B3LYP-D3­(BJ)/6-311G**­(CH2Cl2,SMD)//B3LYP-D3­(BJ)/def2-SVP­(CH2Cl2,SMD) theoretical level. The noncatalytic reaction occurred via a stepwise mechanism. The first C–C bond was constructed by coupling two pseudo radical centers generated at the most nucleophilic C2 atom in the cyclic enol silyl ether and the most electrophilic terminal Cβ atom in the alkynone, which was responsible for the regioselectivity of the reaction. The counterion NTf2 – could stabilize the Zn­(II) complex by coordinating to the center metal, forming a high-reactivity hexacoordinate Zn­(II)-complex intermediate. The bulky CF3 group in the NTf2 – ion adjusted the blocking effect of o-iPr in aniline of the ligand toward the reactive site (that is, the Cβ atom in the alkynone) and induced the si face of the cyclic enol silyl ether to approach the alkynone from its less hindered re face, achieving a high enanotioselectivity of products. The Pauli repulsion between the Zn­(II)-associated moiety and cyclic enol silyl ether fragment was the main contributor to the stereodifference of the two competing pathways in chiral N,N′-dioxide-Zn­(II)-catalyzed [2 + 2] cycloaddition. The unfavorable steric repulsion between the o-iPr group of aniline in the ligand and tert-butyldimethylsilyl (TBS) in the cyclic enol silyl ether along the re face path translated into a more destabilizing ΔE Pauli value, leading to the predominant cycloaddition product (P-RR) observed in experiments. Variation of the linkage and chiral backbone could affect the repulsion among the o-iPr in the ligand, the counterion NTf2 –, and substrates, leading to different stereochemical outcomes. These results are in good agreement with experimental observations.