Robby Vroemans

Metal-catalyzed C−H functionalization of aldehydes and ketones has recently significantly grown thanks to a concept of transient directing group. In this strategy, the directing group is generated in situ which limits the functional group manipulation as well as allows new reactivities. This review presents the latest research works carried out in this area over the period 2020–2023.

Abstract

In order to directly functionalize C−H bonds of complex molecules and, in particular, to control the regioselectivity of the reaction, a wide range of directing groups has been used. However, these directing groups need to be installed and removed for further applications, which may limit the use of C−H activation in synthesis. Concerning aldehydes and ketones, a transient directing group strategy has recently emerged to overcome this drawback. The addition of an additive, in general an amine, allowed the in situ formation of the real directing group to achieve C−H activation. This review presents the latest developments in the field over the period 2020–2023.

Abstract

A step-economical and operationally simple nickel-catalyzed cross-electrophile coupling of aryl phosphates with aryl bromides through C−O bond cleavage, which precluded the employment of relatively moisture-labile and unreadily available organometallics, was developed. The reaction proceeded smoothly in the presence of magnesium turnings and lithium chloride in THF to afford the corresponding biaryls in moderate to good yields with reasonable functionality tolerance.

Nature Methods, Published online: 03 July 2023; doi:10.1038/s41592-023-01920-0

Publication date: 28 July 2023

Source: Tetrahedron Letters, Volume 125

Author(s): Ramteke Prachi, Manjinder Singh Gill

Use of mechanochemistry enabled the rapid in situ generation of Grignard reagents, thereby overcoming the longstanding limitations of the Magnesium-mediated Barbier reaction in solution.

Abstract

Organomagnesium halides (Grignard reagents) are essential carbanionic building blocks widely used in carbon-carbon and carbon-heteroatom bond-forming reactions with various electrophiles. In the Barbier variant of the Grignard synthesis, the generation of air- and moisture-sensitive Grignard reagents occurs concurrently with their reaction with an electrophile. Although operationally simpler, the classic Barbier approach suffers from low yields due to multiple side reactions, thereby limiting the scope of its application. Here, we report a mechanochemical adaptation of the Mg-mediated Barbier reaction, which overcomes these limitations and facilitates the coupling of versatile organic halides (e.g., allylic, vinylic, aromatic, aliphatic) with a diverse range of electrophilic substrates (e.g., aromatic aldehydes, ketones, esters, amides, O-benzoyl hydroxylamine, chlorosilane, borate ester) to assemble C−C, C−N, C−Si, and C−B bonds. The mechanochemical approach has the advantage of being essentially solvent-free, operationally simple, immune to air, and surprisingly tolerant to water and some weak Brønsted acids. Notably, solid ammonium chloride was found to improve yields in the reactions of ketones. Mechanistic studies have clarified the role of mechanochemistry in the process, indicating the generation of transient organometallics facilitated by improved mass transfer and activation of the surface of magnesium metal.

An updated bioeconomy perspective on biobased green chemistry routes to high-purity silicon and silica in the context of societal, economic and environmental trends reshaping chemical productions is presented.

Abstract

This study offers an updated bioeconomy perspective on biobased routes to high-purity silicon and silica in the context of the societal, economic and environmental trends reshaping chemical processes. We summarize the main aspects of the green chemistry technologies capable of transforming current production methods. Coincidentally, we discuss selected industrial and economic aspects. Finally, we offer perspectives of how said technologies could/will reshape current chemical and energy production.

Synthesis
DOI: 10.1055/a-2096-6841

We have developed a new method for the synthesis of carbamates from amine and hydrazine formate. The reaction occurs in the presence of iodine and tert-butyl hydroperoxide, in which carbazates are produced via alkoxycarbonyl radical formation for cross-coupling reaction. The method exhibits broad functional group tolerance and affords a series of N-phenylcarbamates in moderate to good yields. Remarkably, our approach is metal free and utilizes cheap, readily available raw materials and relatively universal substrates.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
Table of contents  |  Abstract  |  Full text

Publication date: August 2023

Source: Molecular Catalysis, Volume 547

Author(s): Zong-Pin Fu, Yun-Peng Zhao, Fa-Peng Wu, Jin-Xuan Xie, Le-Le Qiu, Jian Xiao, Jing Liang, Yong-Hui Bai, Fang-Jing Liu, Jing-Pei Cao

The catalytic carbonylation of acrylic acid is achieved, enabling the synthesis of succinic anhydride from renewable resources. This high-yield and selective method can be scaled-up, and alternative sources of CO or green solvents can be used.

Abstract

Alternative sources for polymeric materials have been sought in the past few years to reduce our dependence on fossil feedstock. We report the catalytic carbonylation of acrylic acid, a platform chemical that can be bio-sourced, as a new pathway toward the formation of a useful monomer to polyesters, namely succinic anhydride. The novel system reported herein tackles the difficult carbonylation of unsaturated carboxylic acids through the utilization of an Earth-abundant metal catalyst, [Co₂(CO)₈], in presence of a bidentate ligand, 1,2-bis(dicyclohexylphosphino)ethane (dcpe), and H₂. We investigated the influence of the reaction conditions through the variations of metal, ligand, temperature, pressure, and gas composition. The carbonylative ring-closure of acrylic acid was successfully obtained in high yield and selectivity toward the formation of succinic anhydride using mild conditions (90 °C and 16 bar of CO/H₂ 95 : 5).

A novel NBS-mediated direct thiol-disulfide exchange reaction has been described for the construction of various unsymmetrical disulfides at room temperature under metal-free conditions. More than 30 examples of unsymmetrical disulfides were isolated in good yields (up to 93 %). Captopril, an angiotensin-converting enzyme inhibitor, was able to form the corresponding unsymmetrical disulfide in 61 % yield.

Abstract

A metal-free and N-Bromosuccinimide (NBS)-mediated direct thiol-disulfide exchange reaction at room temperature is developed. A variety of unsymmetrical disulfides have been prepared with good to excellent yields. Efficient late-stage modification of amino acids and drugs demonstrates the utility of this strategy. In addition, easy to operate, broad substrate scope and good functional group tolerance further demonstrate that this reaction provides an essential complementary route to access unsymmetrical disulfides.

The Cover Feature illustrates the photochemical conversion of carboxylic acids to Weinreb and morpholine amides. Sunlight or LED 370 nm irradiation mediates the direct coupling of carboxylic acids to N,O-dimethylhydroxylamine or morpholine in the presence of 4-dimethylaminopyridine and bromotrichloromethane, providing the corresponding amides in satisfactory to high yields. More information can be found in the Research Article by C. G. Kokotos, G. Kokotos et al.