Ewoud

A novel flow electrochemical reactor that accomplishes electrolysis within a few seconds was developed, enabling flash generation of short-lived carbocations and trapping reaction with nucleophiles before they decompose. The present methodology was applied to highly reactive oxocarbenium ions, N-acyliminium ions, glycosyl cations, and the Ferrier cations. Moreover, continuous and flash synthesis of a pharmaceutical precursor using the flow reactor system was successfully demonstrated.

Abstract

A novel flow electrochemical reactor that accomplishes electrolysis within a few seconds in a single passage was developed. By using the flow reactor system, the flash electrochemical generation of short-lived carbocations, including oxocarbenium ions, N-acyliminium ions, glycosyl cations, and Ferrier cations was achieved within a few seconds, enabling the subsequent reaction with nucleophiles before their decomposition. Moreover, continuous operation based on the present system enabled the rapid synthesis of pharmaceutical precursors on demand.

Heterogeneous catalysts were successfully prepared by encapsulating palladium diphosphine complexes into TPB-DMTP-COF by a one-pot self-assembly method. The resulting [Pd]@COF hybrids with highly dispersed Pd−P,P sites performed well in the catalytic methoxycarbonylation of both aliphatic and aromatic olefins.

Abstract

In this study, palladium-based heterogeneous catalysts were successfully prepared by encapsulating the palladium diphosphine complexes into an imine-linked 2D-COF (TPB-DMTP-COF) through a one pot self-assembly approach. It not only prevents the oxidation of phosphine-based ligand during the stepwise impregnation but also suppresses the coordination of imine linkers at the COF host to the palladium guest, thus enabling highly efficient encapsulation of the active bidentate phosphine chelated palladium complex by the widely explored imine-linked COF. Besides, the dosage of diphosphine ligand (Xantphos-SO₃H, L) and the ratio of palladium to L in the preparation of [Pd]@COF hybrids can be readily adjusted under such one pot procedure to satisfy the requirement of crystallinity, porosity, active sites, and CO adsorption capacity for the catalytic performance in the methoxycarbonylation of olefins. The resultant [Pd]@COF-A-0.25-0.5 provides satisfied catalytic performance for both aliphatic and aromatic olefins with total esters up to 92.1 % under optimized conditions. These findings provide the basis for a novel design concept to design heterogeneous catalysts with high efficiency for reaction processes comprising the alkoxycarbonylation of olefins.

A metal-free DDQ catalyzed depolymerization strategy was developed to transform lignin models or natural lignin into various benzimidazole containing compounds (up to 94 % yield). Both β-C and γ-C atoms of lignin can be also utilized to produce desirable products. More importantly, this method can realize the oxidation, degradation and valorization of natural lignin in an one-pot manner.

Abstract

It is a challenging task to simultaneously achieve selective depolymerization and valorization of lignin due to their complex structure and relatively stable bonds. We herein report an efficient depolymerization strategy that employs 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as oxidant/catalyst to selectively convert different oxidized lignin models to a wide variety of 2-phenylbenzimidazole-based compounds in up to 94 % yields, by reacting with o-phenylenediamines with varied substituents. This method could take full advantage of both C_β and/or C_γ atom in lignin structure to furnish the desirable products instead of forming byproducts, thus exhibiting high atom economy. Furthermore, this strategy can effectively transform both the oxidized hardwood (birch) and softwood (pine) lignin into the corresponding degradation products in up to 45 wt% and 30 wt%, respectively. Through a “one-pot” process, we have successfully realized the oxidation/depolymerization/valorization of natural birch lignin at the same time and produced the benzimidazole derivatives in up to 67 wt% total yields.

Going to plan: Olefins have been hydroxymethylated by using an iridium catalyst and the synergy of two ligands. DFT calculations provided a chance to develop new catalytic systems before empirical studies were undertaken. Then the iridium-catalyzed domino hydroformylation/reduction of olefins to alcohols under water–gas shift reaction conditions was studied as an example. Two different ligands (L1 and L10) applied at the same time improved alcohol yields and verified the computational model.

Abstract

A novel one-pot iridium-catalyzed domino hydroxymethylation of olefins, which relies on using two different ligands at the same time, is reported. DFT computation reveals different activities for the individual hydroformylation and hydrogenation steps in the presence of mono- and bidentate ligands. Whereas bidentate ligands have higher hydrogenation activity, monodentate ligands show higher hydroformylation activity. Accordingly, a catalyst system is introduced that uses dual ligands in the whole domino process. Control experiments show that the overall selectivity is kinetically controlled. Both computation and experiment explain the function of the two optimized ligands during the domino process.

Nature Catalysis, Published online: 08 December 2021; doi:10.1038/s41929-021-00726-7

Nature Reviews Chemistry, Published online: 03 December 2021; doi:10.1038/s41570-021-00346-6

The Front Cover illustrates a concept to switch the raw material basis for plasticizer production from fossil to bio-based feedstocks. The bicyclic plasticizers, which were synthesized as target molecules, are accessible from bio-based 2-methylfuran, maleic anhydride and 2-ethylhexanol. Evaluating the performance of this new bio-based plasticizer generation revealed promising plasticizing properties. More information can be found in the Full Paper by R. Otter, A. Liese, H. Gröger et al.

An alternative route is developed to prepare PCTA monomer with plant-based acrylate and acetaldehyde as the feedstocks. The features include catalytic MBH reaction, one-step dehydration/Diels–Alder reaction over H₂SO₄/SiO₂ catalyst, and Pd/C-catalyzed dehydrogenation. In addition, commonly used plasticizer di(2-ethylhexyl) benzenedicarboxylate and monomer UNOXOL™ diol can also be manufactured.

Abstract

PCTA is an important copolyester that has been widely used in our daily necessities. Currently, its monomers are industrially produced from petroleum-derived xylene. To reduce the reliance on fossil energy, we herein disclose an alternative route to access PCTA monomer (terephthalate/isophthalate=2.4/1) in 61 % overall yield using plant-based acrylate and acetaldehyde as the feedstocks. The process includes Morita–Baylis–Hillman (MBH) reaction of acetaldehyde with acrylate, subsequent one-step dehydration/Diels–Alder reaction with acrylate over H₂SO₄/SiO₂ catalyst, and final Pd/C-catalyzed dehydrogenation. Besides, when varying the final step to hydrogenation, another important monomer UNOXOL™ diol (1,4-trans/1,4-cis/1,3-trans/1,3-cis=5.2/2/2.5/1) can be produced in 67 % overall yield.

Boc-kle up: An atom-economic synthesis of N-tert-butoxycarbonyl (N-Boc) amines from amines, t-butanol, and CO is reported at room temperature with commercially available AuCl₃/CuI as catalysts. Gram-scale preparation of medicinally important N-Boc amine intermediates is achieved, which demonstrates a potential application prospect in industrial syntheses.

Abstract

N-tert-butoxycarbonyl (N-Boc) amines are useful intermediates in synthetic/medicinal chemistry. Traditionally, they are prepared via an indirect phosgene route with poor atom economy. Herein, a step- and atom-economic synthesis of N-Boc amines from amines, t-butanol, and CO was reported at room temperature. Notably, this N-tert-butyloxycarbonylation procedure utilized ready-made substrates, commercially available AuCl₃/CuI as catalysts, and O₂ from air as the sole oxidant. This catalytic system provided unique selectivity for N-Boc amines in good yields. More significantly, gram-scale preparation of medicinally important N-Boc amine intermediates was successfully implement, which demonstrated a potential application prospect in industrial syntheses. Furthermore, this approach also showed good compatibility with tertiary and other useful alcohols. Investigations of the mechanisms revealed that gold catalyzed the reaction and copper acted as electron transfer mediator in the catalytic cycle.

Nature Communications, Published online: 16 November 2021; doi:10.1038/s41467-021-26960-y

A general and selective synthesis of amines via hydroaminomethylation of olefins in the presence of the specific Co-tert-BuPy-Xantphos catalyst is presented. This novel system is complementary to previously known noble metal catalysts and constitutes one of the most general catalysts for HAM.

Abstract

A new cobalt catalyst is presented for the domino hydroformylation-reductive amination reaction of olefins. The optimal Co-tert-BuPy-Xantphos catalyst shows good to excellent linear-to-branched (n/iso) regioselectivity for the reactions of aliphatic alkenes with aromatic amines under mild conditions. This system is far more selective than traditional cobalt(I) catalysts and even better than most known rhodium catalysts.