Robby Vroemans

Nature Chemistry, Published online: 07 April 2021; doi:10.1038/s41557-021-00664-8

The formation of all-carbon quaternary centres is a challenging problem in organic chemistry, with far-reaching implications for functional molecule discovery. Now an inventive solution has been developed, using sulfinamides as traceless linkers for an asymmetric radical Truce–Smiles rearrangement.

Gamma (γ)-valerolactone (GVL) is a promising liquid for energy and carbon-based chemicals. Although many researches regarding the GVL synthesis from carbohydrate biomass, most of them involve the use of noble metals accompanying with the high-purity and high-pressure gaseous hydrogen, existing high cost in large-scale application and safety risk during the transportation and operation process. In this paper, the cheap metal Fe was employed as a reductant for splitting water to produce hydrogen under mild hydrothermal conditions, and commercial Raney Ni was used as a catalyst for in situ hydrogenation of biomass-derived levulinic acid (LA). More than 95% yield of GVL can be attained at 150 oC for 2 h and ~ 90% yield of GVL was also achieved at 100 oC by increasing the reaction time to 5 h. Furthermore, Raney Ni remains the stable catalytic activity after being recycled for 4 times at 150 oC. This work provides a safe and facile process for highly efficient hydrogenation of biomass-derived LA to GVL without precious metals.

Abstract

A palladium-catalysed tandem cyclisation reaction of amidoximes, isocyanides and amines to produce 5-aminoimidazoles was developed. Various 5-aminoimidazoles were prepared in good to excellent yields under mild conditions. This elegant domino process involves the effective cleavage of the N−O bond and the formation of new C−C and C−N bonds in a single operation.

Prospective energy scenarios usually rely on Carbon Dioxide Removal (CDR) technologies to achieve the climate goals of the Paris Agreement. CDR technologies aim at removing CO2 from the atmosphere in a permanent way. However, the implementation of CDR technologies typically comes along with unintended environmental side-effects such as land transformation or water consumption. These need to be quantified before large-scale implementation of any CDR option by means of Life Cycle Assessment (LCA). Direct Air Carbon Capture and Storage (DACCS) is considered to be among the CDR technologies closest to large-scale implementation, since first pilot and demonstration units have been installed and interactions with the environment are less complex than for biomass related CDR options. However, only very few LCA studies - with limited scope - have been conducted so far to determine the overall life-cycle environmental performance of DACCS. We provide a comprehensive LCA of different low temperature DACCS configurations - pertaining to solid sorbent-based technology - including a global and prospective analysis.

Nature Reviews Drug Discovery, Published online: 31 March 2021; doi:10.1038/d41573-021-00063-1

FDA approves first BCMA-targeted CAR-T cell therapy

The hydrodeoxygenation of guaiacol is modelled over a (100) β-Mo2C surface using density functional theory and microkinetic simulations. The thermochemistry of the process shows that the demethoxylation of the guaiacol, to form phenol, will be the initial steps, with a reaction energy of 29 kJ/mol (i.e. endothermic) and a highest activation barrier of 112 kJ/mol. Subsequently, the dehydroxylation of the phenol, which has a rate-determining activation barrier of 145 kJ/mol, will lead to the formation of benzene, with an overall reaction energy for conversion from guaiacol of -91 kJ/mol (i.e. exothermic). The sp2 and sp hybridized carbon atoms of the molecular functional groups are found to dissociate on the surface with minimum energy barriers, while the hydrogenation of the adsorbed molecules requires higher energy. The microkinetic modelling, which is performed considering typical reaction conditions of 500 to 700 K, and a partial pressure ratio H2:guaiacol of 1, shows quick formation and accumulation of phenol on the surface with increasing temperature, although high temperatures mitigate the guaiacol adsorption step. Based on simulated temperature programmed desorption (TPD), maximum conversion of guaiacol can be expected at 70% surface coverage of this species.

Biologically accessible hydroxylation in nature often proceeds through a radical rebound process. However, such a radical rebound usually leads to non-stereoselectivity. Rendering the radical rebound enantioselective is quite challenging. Herein, the first radical asymmetric aminoazidation and diazidation on acyclic systems via radical rebound is reported.

Abstract

Asymmetric aminoazidation and diazidation of alkenes are straightforward strategies to build value-added chiral nitrogen-containing compounds from feedstock chemicals. They provide direct access to chiral organoazides and complement enantioselective diamination. Despite the advances in non-asymmetric reactions, asymmetric aminoazidation or diazidation based on acyclic systems has not been previously reported. Here we describe the iron-catalyzed intermolecular asymmetric aminoazidation and diazidation of styrenes. The method is practically useful and requires relatively low loading of catalyst and chiral ligand. With mild reaction conditions, the reaction can be completed on a 20 mmol scale. Studies of the mechanism suggest that the reaction proceeds via a radical pathway and involves stereocontrol of an acyclic free radical which probably takes place through a group transfer mechanism.

Nature Chemistry, Published online: 22 March 2021; doi:10.1038/s41557-021-00650-0

Although many natural products and drug molecules contain N–N linkages, the chemistry of N–N coupling is somewhat underdeveloped. Now, a nitrene-mediated intermolecular N–N coupling of dioxazolones and arylamines that relies on iridium or iron catalysis has been developed. These reactions offer a simple and efficient method for the synthesis of hydrazides from readily available precursors.

A brominated supported Ru catalyst was developed for the cleavage of C−O linkages in aryl ethers (reaching yield 90.3 % to monoaromatics from diphenyl ether) in lignin compounds without hydrogenation of the aromatic rings. Both selective poisoning of terrace sites and electronic promotion of defect sites contribute to the catalytic performance.

Abstract

The cleavage of C−O linkages in aryl ethers in biomass-derived lignin compounds without hydrogenation of the aromatic rings is a major challenge for the production of sustainable mono-aromatics. Conventional strategies over the heterogeneous metal catalysts require the addition of homogeneous base additives causing environmental problems. Herein, we propose a heterogeneous Ru/C catalyst modified by Br atoms for the selective direct cleavage of C−O bonds in diphenyl ether without hydrogenation of aromatic rings reaching the yield of benzene and phenol as high as 90.3 % and increased selectivity to mono-aromatics (97.3 vs. 46.2 % for initial Ru) during depolymerization of lignin. Characterization of the catalyst indicates selective poisoning by Br of terrace sites over Ru nanoparticles, which are active in the hydrogenation of aromatic rings, while the defect sites on the edges and corners remain available and provide higher intrinsic activity in the C−O bond cleavage.

A recent report in Nature Catalysis detailed the potentially paradigm-shifting organocatalysis of Suzuki cross-coupling of aryl halides with aryl boronic acids, catalysed by simple amine species. We have conducted a reinvestigation of key claims in this paper across multiple academic and industrial laboratories that shows that the observed catalytic activity cannot be due to the amine, but rather is due to tricyclohexylphosphine palladium complexes that are readily entrained during the purification of the amine.

Not just Hünig's base! Siegfried Hünig's 100th birthday is a good time to recall the fundamental work of this versatile chemist. His group studied reactive intermediates, synthetic methods, and unique target compounds. The central leitmotif of his research was the synthesis and behavior of dyes, redox systems, and organic metals. Hünig started his career during World War II and for 65 years he was a distinguished scientist and teacher.

Abstract

Examples from different research areas of Siegfried Hünig are displayed to remind us that organic chemistry owes much more than Hünig's base to this exceptionally versatile and creative chemist. The main research lines dealing with the synthesis and physical characterization of new dyes, multistage redox systems, and organic metals will be presented as well as his contributions to enamine chemistry, the discovery of diimine as a hydrogenation agent, and nucleophilic acylation with trimethylsilyl cyanide, which are less well‐known nowadays. In addition, exotic compounds with parallel C=C and N=N bonds were systematically studied in Hünig's group. Reflecting on the development of his research demonstrates both the importance of a systematic approach and how fruitful entirely unexpected results are if they meet a “well‐prepared mind”. During Hünig's academic career, teaching played an indisputable role. His efforts in modernizing the chemistry institute at Würzburg and his support of young researchers in the academic system in Germany are also highlighted.

Publication date: 15 June 2021

Source: Coordination Chemistry Reviews, Volume 437

Author(s): Rui-Han Gao, Ying Huang, Kai Chen, Zhu Tao

An approach to selectively transform C_γ−H bonds of alicyclic amines to C_γ(sp³)−halogen, oxygen, nitrogen, boron, and sulfur bonds is described. This method is enabled via the pre‐complexation of the amine substrate with palladium followed by the addition of oxidant to yield bioactive motifs functionalized at the γ‐position.

Abstract

This paper describes a new method for the transannular functionalization of the γ‐C−H bonds in alicyclic amines to install C(sp³)−halogen, oxygen, nitrogen, boron, and sulfur bonds. The key challenge for this transformation is controlling the relative rate of C_γ−H versus C_α−H functionalization. We demonstrate that this selectivity can be achieved by pre‐complexation of the substrate with Pd prior to the addition of oxidant. This approach enables the use of diverse oxidants that ultimately install various heteroatom functional groups at the γ‐position with high site‐ and diastereoselectivity.