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Aldehyde unaffected: Selective carbonylative esterification of 5-HMF was achieved on a polystyrene-supported palladium (Pd@PS) catalyst with aryl halides as coupling partner. Using oxalic acid as a solid and environmentally benign CO source avoided the need for highly sophisticated equipment to trap CO gas. A series of aryl esters of 5-HMF were synthesized in good-to-moderate yield by overcoming the issue of decarbonylation.

Abstract

A decarbonylation free, polystyrene-supported, Pd (Pd@PS)-catalysed carbonylative esterification of the hydroxy group of 5-hydroxymethyl furfural (5-HMF) to its corresponding aryl esters has been developed. The use of Pd@PS, oxalic acid as CO source, and aryl halides was first explored for the aryl ester of 5-HMF synthesis. Here, we investigated the vital role of a polystyrene support to avoid the commonly known decarbonylation of 5-HMF. The reaction exhibits vast substrate scope with comparably good yield and catalyst recyclability.

Nature, Published online: 06 July 2021; doi:10.1038/d41586-021-01846-7

Green amination: Sodium butylated hydroxytoluene (NaBHT) has been shown to be a highly efficient base for the solvent-free (melt) amination of a wide variety of substrates, including those containing base-sensitive and redox-active functional groups.

Abstract

NaBHT (sodium 2,6-di-tert-butyl-4-methylphenolate), a strong, but hindered and lipophilic base, has been effectively paired with similarly lipophilic, high-reactivity Pd-NHC (N-heterocyclic carbene) catalysts to produce an ideal combination for performing solvent-free (melt) cross-coupling amination. The mild nucleophilicity of NaBHT, coupled with the anti-oxidant properties of its conjugate acid byproduct, BHT means the process seems to have no functional group incompatibilities. Highly effective coupling of base-sensitive and redox-active functional groups was observed in all cases with only 0.1–0.2 mol percent catalyst. Comparisons using the standard base for this reaction, KOtBu, led to poor couplings or complete degradation in most applications – only NaBHT works.

Nature, Published online: 29 June 2021; doi:10.1038/d41586-021-01724-2

Nature Reviews Chemistry, Published online: 22 June 2021; doi:10.1038/s41570-021-00288-z

Bridged bicyclic nitrogen scaffolds are conformationally restricted analogues of important aminocarbo- and aminoheterocycles. Fixation of functional groups in a biologically active conformation provides efficient and selective ligands for various targets, featuring improved ADME parameters. Long synthetic sequences relying on traditional organic chemistry currently limit the drug discovery process. New step-economic synthetic procedures are therefore highly sought after.

Abstract

Bridged nitrogen bicyclic skeletons have been accessed via unprecedented site- and diastereoselective orthogonal tandem catalysis from readily accessible reactants in a step economic manner. Directed Pd-catalyzed γ-C(sp³)-H olefination of aminocyclohexane with gem-dibromoalkenes, followed by a consecutive intramolecular Cu-catalyzed amidation of the 1-bromo-1-alkenylated product delivers the interesting normorphan skeleton. The tandem protocol can be applied on substituted aminocyclohexanes and aminoheterocycles, easily providing access to the corresponding substituted, aza- and oxa-analogues. The Cu catalyst of the Ullmann-Goldberg reaction additionally avoids off-cycle Pd catalyst scavenging by alkenylated reaction product. The picolinamide directing group stabilizes the enamine of the 7-alkylidenenormorphan, allowing further product post functionalizations. Without Cu catalyst, regio- and diastereoselective Pd-catalyzed γ-C(sp³)-H olefination is achieved.

The by-product (called humins) is accompanied by a one-pot catalytic conversion reaction of furfural (FAL) to isopropyl levulinate (PL), which is carbonized (Humins-700) and applied to a new experiment of electromagnetic wave absorption, showing superior electromagnetic wave absorption performance. The minimum reflection loss (RLmin) value is −47.3 dB at 13.0 GHz with a thickness of 2.0 mm. This provides inspiration that humins can be applied to electromagnetic wave absorption.

Abstract

Both one-pot catalytic conversion of furfural (FAL) to isopropyl levulinate (PL) and carbonization of by-product (humins) for electromagnetic wave absorption are discussed, which provides inspiration that humins can be applied to electromagnetic wave absorption. In the former, phosphotungstic acid (PW) is employed as a homogeneous catalyst to convert FAL to PL via a tandem reaction in one pot, with the formation of a vast amount of humins. With FAL and various intermediates as substrates, it was found that humins was a polymerization product of FAL, furfuryl alcohol (FOL) and furfuryl ester (FE) with furan rings. In addition, the in situ attenuated total reflection infrared (ATR-IR) spectra also provided a basis for the proposed reaction route. In the latter, with the humins as raw material, P species and WO₃ doped nano-porous carbon (Humins-700) platform formed after high-temperature annealing is used for electromagnetic wave absorption and manifests desirable absorption performance. The minimum reflection loss (RL_min) value is −47.3 dB at 13.0 GHz with a thickness of 2.0 mm and the effective absorption bandwidth reaches 4.5 GHz (11.2–5.7 GHz).