Robby Vroemans

Recent advances in the carbon-nitrogen/carbon-oxygen (C−N/C−O) bond formation reactions under transition-metal-free conditions are systematically reviewed. In particular, amination, amidation, etherification and hydroxylation reactions with the aid of various promoters/catalysts (mainly including alkali-metal-based salts and organic molecules) are comprehensively described. Besides, the potential applications of these synthetic protocols in various fields are also presented.

Abstract

Carbon-heteroatom bond formation under transition-metal free conditions provides a powerful synthetic alternative for the efficient synthesis of valuable molecules. In particular, C−N and C−O bonds are two important types of carbon-heteroatom bonds. Thus, continuous efforts have been deployed to develop novel C−N/C−O bond formation methodologies involving various catalysts or promoters under TM-free conditions, which enables the synthesis of various functional molecules comprising C−N/C−O bonds in a facile and sustainable manner. Considering the significance of C−N/C−O bond construction in organic synthesis and materials science, this review aims to comprehensively present selected examples on the construction of C−N (including amination and amidation) and C−O (including etherification and hydroxylation) bonds without transition metals. Besides, the involved promoters/catalysts, substrate scope, potential application and possible reaction mechanisms are also systematically discussed.

Catalysts, Vol. 13, Pages 651: Atomically Dispersed Pd Sites on ZrO2 Hybridized N-Doped Carbon for Efficient Suzuki–Miyaura Reaction

Catalysts doi: 10.3390/catal13040651

Authors: Jiaqi Du Yidan Peng Xu Guo Guoliang Zhang Fengbao Zhang Xiaobin Fan Wenchao Peng Yang Li

Researchers studying heterogeneous catalysis are intrigued by single-atom catalysts (SACs) due to their ultrahigh atomic utilization. However, only a few reports on SAC-catalyzed classical organic transformations are available. In this work, atomically dispersed Pd sites are confined to a ZrO2 hybridized N-doped carbon skeleton with a smart design. UiO-66-NH2 is used to anchor Pd atoms by the coordination of the donor atoms including lone pairs of electrons and metal atoms. Subsequently, the in situ introduction of ZrO2 doping is achieved using pyrolysis, which helps improve the catalytic performance by modulating the electronic state. The Pd@ZrO2/N–C catalyst obtained from the unique design exhibits a high yield (99%) in eco-friendly media with an extremely low noble metal dosage (0.03 mol% Pd) for the Suzuki reaction. Moreover, Pd@ZrO2/N–C remains highly active after being reused several times and possesses versatility in a variety of substrates. This strategy offers a feasible alternative to designing SACs with atomically dispersed noble metals for heterogeneous reactions.

“This study brings C−N atroposelectivity outside of the hands of a few methodology experts, and into the hands of general organic chemists, biochemists, medicinal chemists, etc.” This and more about the story behind the front cover can be found in the article at 10.1002/chem.202300279).

Abstract

Invited for the cover of this issue is the group of Frederic W. Patureau at the RWTH Aachen University. The image depicts atropoisomerism, in particular through the helix-shaped vines in the forefront focus. This metaphorically illustrates the importance of atroposelectivity in biologically active molecules, such as in the 5-hydroxyindoles that were accessed through the first enantioselective Nenitzescu indole synthesis. Read the full text of the article at 10.1002/chem.202300279.

An atroposelective copper-catalyzed three-component coupling of cyclic diaryliodonium, cyanate and phenols is used to synthesize axially chiral carbamates. The success of this coupling is attributed to the key dual role of phenols, which are capable of activating the copper catalyst and trapping the isocyanate intermediate.

Abstract

A copper-catalyzed atroposelective ring-opening reaction of cyclic diaryliodoniums, sodium cyanate (NaOCN) and phenols is reported. The reaction chemoselectively affords axially chiral carbamates by sequential coupling of cyclic diaryliodonium and NaOCN, followed by phenol. Mechanistic investigations revealed that phenol is not only a reagent to trap highly active intermediate isocyanates, but it also activates the copper catalyst as a standby ligand. The carbamates were readily transformed into highly functionalized urea derivatives within a simple nucleophilic substitution reaction.

Single-atom catalysts, featuring atomically dispersed metals on solid carriers, offer limitless possibilities for new, sustainable transformations in the chemical sector. These materials bridge the gap between organometallic and nanoparticle catalysis and are opening exciting avenues for mimicking metalloenzymes. This Review summarizes the impressive progress and potential knowledge gaps in the use of single-atom catalysts in organic synthesis.

Abstract

Single-atom catalysts hold the potential to significantly impact the chemical sector, pushing the boundaries of catalysis in new, uncharted directions. These materials, featuring isolated metal species ligated on solid supports, can exist in many coordination environments, all of which have shown important functions in specific transformations. Their emergence has also provided exciting opportunities for mimicking metalloenzymes and bridging the gap between homogeneous and heterogeneous catalysis. This Review outlines the impressive progress made in recent years regarding the use of single-atom catalysts in organic synthesis. We also illustrate potential knowledge gaps in the search for more sustainable, earth-abundant single-atom catalysts for synthetic applications.

Isocyanides, thanks to their multiple reactivities, are the main players in multicomponent reactions. While traditional approaches exploit their two-electrons reactivity, they are currently “on stage”, shining in a new light thanks to the development of visible light photochemical reaction conditions. For more information, see the Review by Gian Cesare Tron and Mariateresa Giustiniano et al. (DOI: 10.1002/chem.202203150).

Merging transition metal catalysis with electrochemical oxidation has emerged as a potential catalyst system for C−H bond functionalization, avoiding the use of chemical-based oxidants. Electrochemically promoted electrooxidation of the metal catalyst offers a mild, efficient and atom-economical alternative to traditional chemical oxidant-based systems. This Review highlights recent advances in transition metal-electrocatalyzed C−H functionalization reactions.

Abstract

Electrochemically promoted transition metal-catalyzed C−H functionalization has emerged as a promising area of research over the last few decades. However, development in this field is still at an early stage compared to traditional functionalization reactions using chemical-based oxidizing agents. Recent reports have shown increased attention on electrochemically promoted metal-catalyzed C−H functionalization. From the standpoint of sustainability, environmental friendliness, and cost effectiveness, electrochemically promoted oxidation of a metal catalyst offers a mild, efficient, and atom-economical alternative to traditional chemical oxidants. This Review discusses advances in the field of transition metal-electrocatalyzed C−H functionalization over the past decade and describes how the unique features of electricity enable metal-catalyzed C−H functionalization in an economic and sustainable way.

Nature, Published online: 01 March 2023; doi:10.1038/d41586-023-00601-4

Synthesis
DOI: 10.1055/a-2019-1532

Under mild irradiation conditions using violet light-emitting diodes, a catalytic amount of a thiolate of N-(4-mercaptophenyl)pivalamide promotes monoselective defluoroalkylation of trifluoroacetates with a variety of aliphatic alkenes in the presence of a formate salt. The reactions allow facile and low-cost synthesis of valuable α,α-difluoro substituted aliphatic carboxylate esters under mild conditions, and demonstrate the dual-functional role of arenethiolates in photocatalysis as both a strong photoreductant in a redox cycle and a hydrogen-atom-transfer catalyst.
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Article in Thieme eJournals:
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Abstract

Iridium-catalyzed α-alkylation of methyl ketones with primary carbohydrate alcohols proceeded via borrowing hydrogen strategy. Protected sugar derivatives having one free primary hydroxyl group reacted with methyl ketones to give the α-alkylation products or alkylated 4,5-unsaturated sugars along with the elimination of an alkoxy group.

Nature Catalysis, Published online: 27 February 2023; doi:10.1038/s41929-023-00933-4