Aminoalcohol derivatives by nickel-catalyzed enantioselective coupling of imines and dienol ethers

The reductive coupling of dienol ethers with N-tosylimines catalyzed by Ni(0) in the presence of a VAPOL-derived phosphoramidite ligand follows an unprecedented regiochemical course; it furnishes syn-configured 1,2-aminoalcohol derivatives in good chemical yields with up to 94% ee.

Homogeneous Catalyzed Valorization of Furanics: A Sustainable Bridge to Fuels and Chemicals

The development of efficient biomass valorization is imperative for the future sustainable production of chemicals and fuels. Particularly, the last decade has witnessed the development of a plethora of effective and selective transformations of bio-based furanics using homogeneous organometallic catalysis under mild conditions. In this review, we describe some of the advances regarding the conversion of target furanics into value chemicals, monomers for high-performance polymers and materials, and pharmaceutical key intermediates using homogeneous catalysis. Finally, the incorporation of furanic skeletons into complex chemical architectures by multifunctionalization routes is also described.

Hydroxymethylation of Furfural to HMF with Aqueous Formaldehyde over Zeolite Beta Catalyst

Hydroxymethylation of 2-furaldehyde (furfural) toward 5-hydroxymethyl-2-furaldehyde (HMF) was examined in this work among various zeolites with an aqueous formaldehyde as a reagent in a batch and a flow reactor system. It was found that the zeolite beta gave high activity and good reusability with calcination treatment before each run for the target reaction in the batch system. The unique stability of the HMF yield in the liquid-flow system was also observed only in the case of zeolite beta. The effect of the SiO2/Al2O3 ratio in the zeolite beta suggested that hydrophobicity would be an important factor in faster hydroxymethylation with an aqueous formaldehyde reagent. The highest turnover frequency (TOF) for HMF production was found to be 2.4 h−1 in the case of zeolite beta with SiO2/Al2O3 = 440 in the batch reactor system. An approximately 30% yield for HMF was achieved under optimum conditions for zeolite beta catalysts.

Iridium-Catalyzed Highly Regioselective and Diastereoselective Allylic Etherification To Access cis-2,6-Disubstituted Dihydropyridinones

A highly regio- and diastereoselective method to access cis-2,6-disubstituted dihydropyridinones under mild conditions by an iridium-catalyzed allylic etherification is reported. cis-2,6-Disubstituted dihydropyridinones are important precursors for the de novo synthesis of the corresponding piperidine alkaloids and iminosugars. This strategy features a broad substrate scope, high yields, and excellent regio- and diastereoselectivities. A π-allyl-Ir intermediate is involved in the mechanism. The strong A^1,3-strain from the tosyl group may also favor the formation of cis-products in this transformation.

Catalytic production of levulinic acid and ethyl levulinate from uniconazole-induced duckweed (Lemna minor)

Duckweed (Lemna minor) with a high starch content of 50.4% was cultivated by uniconazole-induction method. The cultivated duckweed was used to produce value-added chemicals such as glucose, levulinic acid and formic acid in diluted HCl aqueous solution. A high glucose yield of 93.4% (471 g/kg based on loading duckweed mass) could be achieved at 180 °C in short reaction time, and the generated glucose was converted into levulinic acid and formic acid with yields of 52.0% and 34.1%, respectively, for 150 min, corresponding to 262 g/kg levulinic acid yield and 171 g/kg formic acid yield based on the mass of loading duckweed, respectively. Moreover, the duckweed was efficiently converted to ethyl levulinate with 55.2% yield (400.6 g/kg) at 200 °C in ethanol. This work provides a promising strategy for the production of value-added chemicals from phytoplankton that is able to purify the wastewater containing high content of P and N.

Synthesis of 6-Substituted Piperidin-3-ones via Rh(II)-Catalyzed Transannulation of N-Sulfonyl-1,2,3-triazoles with Electron-Rich Aromatic Nucleophiles

A highly diastereoselective rhodium(II)-catalyzed transannulation of aldehyde-tethered N-sulfonyl triazoles with electron-rich aromatic nucleophiles is reported for the first time to afford functionalized 6-substituted piperidin-3-ones. The reaction has a broad substrate scope including both aliphatic and aromatic N-sulfonyl-1,2,3-triazoles together with various aromatic nucleophiles. The addition of a catalytic amount of Lewis acid has proven to be crucial for the yield improvement. By employing this methodology, hardly accessible piperidin-3-ones bearing quaternary carbons could be obtained.

Sustainable Synthesis of Chiral Tetrahydrofurans through the Selective Dehydration of Pentoses

L-Arabinose is an abundant resource available as a waste product of the sugar beet industry. Through use of a hydrazone-based strategy, L-arabinose was selectively dehydrated to form a chiral tetrahydrofuran on a multi-gram scale without the need for protecting groups. This approach was extended to other biomass-derived reducing sugars and the mechanism of the key cyclization investigated. This methodology was applied to the synthesis of a range of functionalized chiral tetrahydrofurans, as well as a formal synthesis of 3R-3-hydroxymuscarine.

Synthesis of Enantiopure 3-Hydroxypiperidines from Sulfinyl Dienyl Amines by Diastereoselective Intramolecular Cyclization and [2,3]-Sigmatropic Rearrangement

The highly diastereoselective base-promoted intramolecular cyclization of a variety of enantiopure sulfinyl dienyl amines provides novel sulfinyl tetrahydropyridines that are readily converted to 3-hydroxy tetrahydropyridines via sigmatropic rearrangement. The influence of N- and C- substituents on the process has been studied. Procedures to shorten the sequence such as the tandem cyclization followed by [2,3]-sigmatropic rearrangement, as well as cyclization of the free amine, under Boc- or ArSO- deprotection conditions have been examined. Good to excellent levels of selectivity are generally observed for the reported transformations (dr: 75/25 to >98/2). A novel protocol to access substituted amino dienyl sulfoxides is also reported.