Search

A catalytic asymmetric vinylogous aldol reaction between β,γ-unsaturated amides and isatins has been developed. In the presence of 10 mol% of tertiary amine-thiourea C7, the vinylogous reaction has been achieved in up to 98% yield and up to 99% ee (26 examples). This methodology provides an efficient approach to construct chiral multifunctional 3-hydroxy-2-oxindoles. Moreover, the transformations of the chiral products, including the esterification of amides, the hydrogenation of the C–C double bond and further conversion to spirolactones, have been investigated. [ABSTRACT FROM AUTHOR]

As a potential substitute for petroleum-based terephthalic acid (TPA) in the manufacture of polyesters, 2,5-furandicarboxylic acid has been obtained through several feasible routes. Herein, a new chemo-enzymatic strategy for generating furan-2,5-dicarboxylic acid (FDCA) precursors from sodium gluconate via bio-oxidation and dehydration is presented. By coupling the bio-oxidation of gluconate 5-dehydrogenase with carbonyl reductase PsCR for cofactor regeneration, 5-keto- D -gluconic acid (5KGA), a specific product of D -gluconic acid bio-oxidation and a stable intermediate, was obtained in 99% yield. The statin intermediate ethyl (S)-4-chloro-3-hydroxybutanoate was simultaneously generated as a co-product via cycling cascade catalysis. Subsequently, the yield of the FDCA precursor n-butyl-5-formyl-2-furancarboxylate (nBu-FFCA) generated via 5KGA dehydration and esterification reached 77.9%. Key intermediate characterization and theoretical calculations revealed that the decarboxylation and dehydration of cyclic 5KGA to furfural was the main side-reaction that prevented a better yield of dehydrated 5KGA. This route demonstrates good sustainability and market competitiveness compared to the existing FDCA synthesis methods. [ABSTRACT FROM AUTHOR]

We developed a novel pathway for preparing the high-value pharmaceutical intermediate 2-furylglyoxylic acid (2FGA) from 2-keto- L -gulonic acid (2KGA), a bio-based sugar-acid monomer and precursor of vitamin C, via dehydration. 100 g L−1 methyl 2-keto- L -gulonicate (Me-2KGA) was transformed into methyl 2-furylglyoxylicate (Me-2FGA) with a maximum yield of 79.4%, competing with the yields obtained via traditional commercial synthesis methods. Subsequently, characterisation methods and theoretical calculations were employed; it was confirmed that natural 2KGA, with a 2,5-cyclic configuration, was esterified initially, it then underwent a transformation to an opened intermediate which further recyclized in a 3,6-cyclic configuration via removing one molecule of water, and this was finally dehydrated to Me-2FGA. This study offers novel insight into the flexibility and versatility of furan-based compounds. [ABSTRACT FROM AUTHOR]

A copper-catalyzed enantioselective alkynylation between terminal alkynes and pyrazole-4,5-diones has been developed. With 2.5 mol% CuI and 3 mol% chiral ligand L15, chiral propargylic alcohols bearing a pyrazolone motif were produced in 82–99% yield and up to 98% ee. Moreover, both enantiomers of the chiral propargylic alcohols were obtained with ligands L12 and L15, respectively. [ABSTRACT FROM AUTHOR]

In this study, the bio-oxidation of galactitol to the valuable d-tagatose is presented. This proposed strategy could start with the refined by-product of waste xylose mother liquor formed by chemical hydrogenation. Through a computationally guided enzyme screening approach, a robust polyol dehydrogenase (PdPDH) was rapidly identified from a massive number of candidates. When coupled with a water-forming NADH oxidase (StNOX) for environmentally benign cofactor regeneration, subsequent reaction optimization facilitated the complete transformation of 100 g L−1 galactitol into the desired product within 15 h, with a yield of 91% in a 2 L scale preparative reaction. Compared to the current enzymatic isomerization system, our approach avoids low conversion, high operative temperatures and by-product formation, while enabling simplified product isolation. [ABSTRACT FROM AUTHOR]

A simple and novel SO2 release method for the synthesis of controllable nanostructured BaSO4 and BaSO3 crystals was developed based on the oxidation of HSO3− to SO42− by dimethyl sulfoxide (DMSO) in a binary system of triethylene glycol (TEG) + DMSO. The binary system was successfully re-used for SO2 absorption and production of BaSO3 crystals at least three times. Aggregation and self-assembly mechanisms for the preparation of BaSO4 and BaSO3 crystals were proposed. This controllable synthesis strategy for BaSO4 and BaSO3 crystals has offered an alternative way for the comprehensive utilization of SO2, and provided a scientific foundation for the development of DMSO oxidation chemistry. [ABSTRACT FROM AUTHOR]

In this study, novel rod-like and block-like CaO crystals were prepared after calcinating three types of CaCO3 precursors containing dumbbell-like, wheat spike-like and microsphere-like morphologies at 1000 °C for 3 h. The CaCO3 precursors were synthesized via the hydrothermal reaction of a CO2 storage-material (CO2SM) with Ca(OH)2 without additional additives. In the preparation process, CO2SM was not only used as a raw material but it also played the role of a directing agent. Moreover, as the major influence factors, CO2SM dosage, reaction temperature, reaction time and Ca2+ concentration were systemically investigated. Subsequently, the possible formation mechanism of the CaCO3 precursors was proposed. Finally, the as-obtained CaO crystals exhibit the adsorption amounts of 14.67, 16.32 and 7.50 mg g−1 for an 8% CO2/N2 mixture at 25 °C. [ABSTRACT FROM AUTHOR]

Different morphologies of CaCO3 micro-particles through a hydrothermal reaction between Ca(OH)2 saturated limpid solution and a new CO2-storage material (CO2SM), which was obtained from an equimolar system 1,2-ethylenediamine (EDA) + 1,2-ethylene glycol (EG) uptaking CO2, were presented without any additives. It's worth noting that the morphologies of the CaCO3 precipitates could be controlled as uniform sheaf-like (pure calcite) at the lower CO2SM concentration (0.6 g L−1) and homogeneous spherical-like (pure vaterite) at the higher CO2SM concentration (40 g L−1) for 1 h at 100 °C, in which the released EDA and/or EG from CO2SM had unexpected functions as surfactants. After the precipitation of CaCO3 crystals in 40 g L−1 CO2SM solution, the filtered solution could not only be reused to absorb CO2, but also to prepare the same crystal phase CaCO3 micro-particles repeatedly with the addition of Ca(OH)2. As a result, this novel synthesis process of CaCO3 micro-particles with CO2SM offers an alternative way for the comprehensive utilization of CO2. [ABSTRACT FROM AUTHOR]

1,2-Diketones are employed, for the first time, as electrophiles in the vinylogous aldol reaction. With 5 mol% of chiral tertiary amine-thiourea , a direct vinylogous aldol-cyclization cascade reaction between β,γ-unsaturated amides and o-quinones has been achieved to produce spirocyclic dihydropyranones in 76-99% yield and 82-95% ee.

The first enantioselective vinylogous aldol-cyclization cascade reaction of allyl pyrazoleamides with isatins is reported. With 1 mol% of Takemoto catalyst, optically active spirocyclic oxindole-dihydropyranones were obtained in excellent yields (93-99%) and good-to-excellent enantioselectivities (82-97% ee).