LongLarf

Two for one: A straightforward chemoenzymatic synthesis pathway towards valuable chiral alcohols with α-fluorination in close proximity to the chiral center and a pyridine ring is presented. High conversions with excellent enantioselectivities were found, showing its high synthetic potential.

Abstract

Fluoro-substituted and heteroaromatic compounds are valuable intermediates for a variety of applications in pharma- and agrochemistry and synthetic chemistry. This study investigates the chemoenzymatic preparation of chiral alcohols bearing a heteroaromatic ring with an increasing degree of fluorination in α-position. Starting from readily available picoline derivatives prochiral α-halogenated acyl moieties were introduced with excellent selectivity and 64–95 % yield. The formed carbonyl group was subsequently reduced to the corresponding alcohols using the alcohol dehydrogenase from Lactobacillus kefir, yielding an enantiomeric excess of 95–>99 % and up to 98 % yield.

Nature, Published online: 13 September 2021; doi:10.1038/s41586-021-03980-8

The missing part: It is well known that hydrothermal processes can be used to convert biomass into solid, liquid, or even gaseous fuels. There are also innumerable scientific reports about the degradation of carbohydrates under hydrothermal conditions yielding especially furanic compounds. Fatty acids, in turn, can be expected to be rather inert during hydrothermal treatment. But what happens to another integral component of biomass: amino acids?

Abstract

Within the past years, hydrothermal processes have gathered much attention as promising conversion technologies for especially wet biomass. Amino acids are an integral component of biomass, zoo biomass in particular. However, what happens to them during hydrothermal treatment? Reviewing the available literature going back to the mid of the 20th century revealed an astonishing, but still fragmentary view. In fact, two universal degradation reactions could be identified (i. e., deamination and decarboxylation), competing with each other. Thereby, small structural differences may obviously have huge impacts on the fate of individual amino acids. Nevertheless, the amount of available experimental data is relatively scarce in many cases. In this work, the available knowledge about the degradation of 20 proteinogenic amino acids under hydrothermal conditions was presented and discussed critically. The hydrothermal conversion of proteinaceus biomass as well as the Maillard reaction, both extensively reviewed elsewhere, were only touched on.

Plastics degradation: An iron photocatalysis system improves the multiple C−H and C−C bond oxidative cleavage of substituted benzenes, applying oxygen as the terminal oxidant to produce benzoic acid selectively. The system is used to degrade styrene-related plastics successfully, even under natural conditions without solvent.

Abstract

Efficient degradation of plastics, the vital challenge for a sustainable future, stands in need of better chemical recycling procedures that help produce commercially valuable small molecules and redefine plastic waste as a rich source of chemical feedstock. However, the corresponding chemical recycling methods, while being generally restricted to polar polymers, need improvement. Particularly, degradation of chemically inert nonpolar polymers, the major constitutes of plastics, suffers from low selectivity and very harsh transformation conditions. Herein, an efficient method was developed for selective degradation of styrene-related plastics under gentle conditions through multiple oxidation of sp³ C−H bonds and sp³ C−C bonds. The procedure was catalyzed with inexpensive iron salts under visible light, using oxygen as green oxidant. Furthermore, simple iron salts could be used to degrade plastics in the absence of solvent under natural conditions, highlighting the potential application of iron salts as additives for degradable plastics.

Palladium-catalyzed remote arylative substitution was achieved for the reaction of arylboronic acids with alkenes possessing a distant acetoxy group via nondissociative chain walking and β-acetoxy elimination.

Abstract

Palladium-catalyzed remote arylative substitution was achieved for the reaction of arylboronic acids with alkenes possessing a distant acetoxy group to provide arylation products having an alkene moiety at the remote position. The use of β-acetoxy elimination as a key step in the catalytic cycle allowed for regioselective formation of unstabilized alkenes after chain walking. This reaction was applicable to various arylboronic acids as well as alkene substrates.

Abstract

The organocatalytic synthesis of substituted vinylene carbonates from benzoins and acyloins was studied using diphenyl carbonate as a carbonyl source. A range of N-Heterocyclic Carbene (NHC) precursors were screened and it was found that imidazolium salts were the most active for this transformation. The reaction occurs at 90 °C under solvent-free conditions. A wide range of substituted vinylene carbonates (symmetrical and unsymmetrical, aromatic or aliphatic), including some derived from natural products, were prepared with 20–99% isolated yields (24 examples). The reaction was also developed using thermomorphic polyethylene-supported organocatalysts as recoverable and recyclable species. The use of such species facilitates the workup and allows the synthesis of vinylene carbonates on the preparative scale (>30 g after 5 runs).

Nature Reviews Chemistry, Published online: 03 September 2021; doi:10.1038/s41570-021-00321-1

Abstract

A three-component thioamination reaction has been developed in the presence of phenyliodonium(III) diacetate (PIDA) leading to the formation of a thioaminated products. This catalytic approach represents a method for the metal-free thioamination of 1,4-naphthoquinone. It was observed that maleimides also work smoothly under this metal-free reaction condition. This present method implies the oxidative coupling reaction through a one-step process with the generation of C−N and C−S bonds. Various aromatic and aliphatic thiols and amines provided the corresponding thioaminated compounds in 62–88% yields. A plausible reaction pathway has been predicted according to few control experiments.

Publication date: 11 November 2021

Source: Chem, Volume 7, Issue 11

Author(s): Si-Shun Yan, Shi-Han Liu, Lin Chen, Zhi-Yu Bo, Ke Jing, Tian-Yu Gao, Bo Yu, Yu Lan, Shu-Ping Luo, Da-Gang Yu

Publication date: 8 October 2021

Source: Tetrahedron, Volume 98

Author(s): Satavisha Kayal, Jun Kikuchi, Naoya Shinagawa, Shigenobu Umemiya, Masahiro Terada

Synlett 2021;
DOI: 10.1055/s-0040-1720393

Ruben Martin is a professor at the Institute of Chemical Research of Catalonia (ICIQ), Tarragona, Spain. He received his Ph.D. in 2003 from the University of Barcelona under the guidance of Prof. Antoni Riera. In 2004, he moved to the Max-Planck Institut für Kohlenforschung as a Humboldt postdoctoral fellow with Prof. Alois Fürstner. In 2005, he undertook further postdoctoral studies at MIT with Prof. Stephen L. Buchwald as a MEC-Fulbright fellow. In 2008, he began his independent career as an assistant professor at the ICIQ (Tarragona). In 2013, he was promoted to associate professor and shortly after to ICREA Research Professor. Ruben Martin has focused his career on designing synthetically useful Ni-catalyzed methodologies for streamlining the preparation of added-value chemicals from simple precursors without losing sight of mechanistic considerations, when appropriate. Gary A. Molander is a professor at the University of Pennsylvania, Philadelphia, United States. He completed his undergraduate studies in chemistry at Iowa State University under the tutelage of Prof. Richard C. Larock. He earned his Ph.D. at Purdue University under the direction of Prof. Herbert Brown and undertook postdoctoral training with Prof. Barry Trost at the University of Wisconsin, Madison. He began his academic career at the University of Colorado, Boulder, moving to the University of Pennsylvania in 1999, where he is currently Professor of Chemistry. His research interests have focused on the utilization of organolanthanides, Pd-catalyzed cross-coupling reactions with trifluoro­borate salts, and the merger of photoredox catalysis and Ni catalysis for tackling a priori uphill transformations under visible-light irradiation for accessing valuable scaffolds in both academic and pharmaceutical laboratories.
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Abstract

In this short essay, I re-emphasize the inter-relationship between mentoring doctoral students or postdocs and the never ending problem of assessing the quality of scientific outputs. It includes the plea to mentees and mentors not to employ an overblown language in papers, posters and lectures, which constitute a gross exaggeration of the true state of affairs. Doubt is also cast on the present use of Hirsch-factors and other bibliometric data as well as certain social media claiming to be effective in assessing scientific quality.

Nature, Published online: 31 August 2021; doi:10.1038/s41586-021-03920-6

Nature, Published online: 01 September 2021; doi:10.1038/s41586-021-03735-5

Indeed interesting and important: Recently published contributions of unusual unsaturated ring strained Group 4 metallocene metallacycles show new aspects of these compounds. Several new investigations of 7- and 5-membered metalla-cyclocumulenes, 5- and 4-membered metalla-cycloallenes as well as metalla-cyclopentynes, complete the understanding of these compounds. From the theoretical point of view and the reactivity they have a great potential for important synthetic applications.

Abstract

Recently published syntheses, reactions and characterizations of unusual unsaturated ring strained Group 4 metallocene metallacycles like metalla-cyclocumulenes, -cycloallenes and -cycloalkynes with different ring size are updated for the last three years. There exist for some of these metallacycles, depending on the ring size, 7-, 5- and 4-membered compounds. The new results for these metallacycles are summarized here and considered in addition to the former published results. Additionally, several compounds of this type were now characterized by new reactions. For a better understanding of these compounds, some spectroscopical methods as well as theoretical calculations were published. Despite of these all-C-metallacycles, only in some cases the syntheses and reactions for the corresponding hetero-metallacycles were published too. Examples for these metallaheterocyclic compounds will not be considered in this article. All these unusual ring strained compounds have a great potential for a lot of interesting synthetic applications in the future. Additionally, they are very interesting from the theoretical point of view.