MRV

Abstract

In recent years, great improvements have been made on palladium‐catalyzed radical reactions. Emerging elegant methodologies of radical involved palladium‐catalyzed transformations provide more and more effective strategies for the construction of complex heterocyclic compounds and applications in drug discovery. It is universally known that Pd(0)/(II)/(IV)‐mediated reactions usually undergo two‐electron transfer processes, while the Pd(I) and Pd(III) involved reactions usually occur via single electron transfer processes. Since our review on palladium radical was published, numurous methodolgies involving palladium radical have sprung up in the past five years. This review further summarized the up‐to‐date transformations toward palladium radical from 2015. For most of these catalytic cycles strategies, plausible mechanisms are demonstrated in detail to give better insight for chemists in need.

Oxidation is a major chemical process to produce oxygenated chemicals in both nature and chemical industry. Currently, industrial deep oxidation processes from polyalkyl benzene are major routes to produce benzoic acids and benzene polycarboxylic acids (BPCAs), while to some extent suffering from the energy-intensive and potentially hazardous drawbacks and the sluggish separation issues. In this report, visible-light-induced deep aerobic oxidation of (poly)alkyl benzene to benzene (poly)carboxylic acids was developed. CeCl3 was proved to be an efficient HAT (Hydrogen Atom Transfer)catalyst in the presence of alcohol as both hydrogen and electron shuttle. Dioxygen (O2) was found as a sole terminal oxidant. In most cases, pure products were easily isolated by simple filtration, showing the advantages of for scaling up. The reaction provides an ideal way to form valuable fine chemicals from abundant petroleum feedstocks.

Arylation of carbonyls, as one of the most common synthetic approaches toward the preparation of alcohols, has received sustained attention since alcohols are important feedstock and building blocks in organic synthesis. Despite recent progress in this field, there remains a considerable challenge to develop an ideal arylation method which features: mild conditions, good functional group tolerance and readily available starting materials. Herein we show that electrochemical arylation can meet this challenge. By taking advantage of synthetic electrochemistry, commercially available aldehydes (ketones) and benzylic alcohols can be readily arylated   to provide a general and scalable access to structurally diverse alcohols (97 examples, >10 gram‐scale). More importantly, convergent paired electrolysis, an ideal but challenging electrochemical technology, has been employed for the first time to transform low value alcohols into more useful alcohols. Detailed mechanistic study suggests that two plausible pathways may be involved in the redox neutral  α ‐arylation   of benzylic alcohols.

Synthesis
DOI: 10.1055/s-0040-1706085

Traditionally, metal-catalyzed cross-coupling reactions rely on stable but expensive metals, such as palladium. However, the recent development of synthetic organic electrochemistry allows for in situ redox manipulations, expanding the use of cheaper, abundant and sustainable metals, such as nickel and copper as efficient cross-coupling catalysts. This short review covers the recent advances in metal-catalyzed electrochemical coupling reactions, with a focus on reactions of sp2 electrophiles and nucleophiles with sp3 coupling partners to form both C–C and C–heteroatom bonds.1 Introduction2 Nickel-Catalyzed C–C sp2–sp3 Coupling Reactions3 Coupling of Aryl Groups with Heteroatomic Nuclei4 Conclusion
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

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Abstract

Palladium(II) precatalysts are used extensively to facilitate cross‐coupling reactions because they are bench stable and give high activity. As a result, precatalysts such as Buchwald's palladacycles, Organ's PEPPSI species, Nolan's allyl‐based complexes, and Yale's 1‐tert‐butylindenyl containing complexes, are all commercially available. Comparing the performance of the different classes of precatalysts is challenging because they are typically used under different conditions, in part because they are reduced to the active species via different pathways. However, within a particular class of precatalyst, it is easier to compare performance because they activate via similar pathways and are used under the same conditions. Here, we evaluate the activity of different allyl‐based precatalysts, such as (η³‐allyl)PdCl(L), (η³‐crotyl)PdCl(L), (η³‐cinnamyl)PdCl(L), and (η³‐1‐tert‐butylindenyl)PdCl(L) in Suzuki‐Miyaura reactions. Specifically, we evaluate precatalyst performance as the ancillary ligand (NHC or phosphine), reaction conditions, and substrates are varied. In some cases, we connect relative activity to both the mechanism of activation and the prevalence of the formation of inactive palladium(I) dimers. Additionally, we compare the performance of in situ generated precatalysts with commonly used palladium sources such as tris(dibenzylideneacetone)dipalladium(0) (Pd₂dba₃), bis(acetonitrile)dichloropalladium(II) (Pd(CH₃CN)₂Cl₂), and palladium acetate. Our results provide information about which precatalyst to use under different conditions.

Chemodivergent cross‐couplings are those in which either one of two (or more) potentially reactive functional groups can be made to react based on choice of conditions. In particular, this review focuses on cross‐couplings involving two different (pseudo)halides that can compete for the role of the electrophilic coupling partner. The discussion is primarily organized by pairs of electrophiles including chloride vs. triflate, bromide vs. triflate, chloride vs. tosylate, and halide vs. halide. Some common themes emerge regarding the origin of selectivity control. These include catalyst ligation state and solvent polarity or coordinating ability. However, in many cases, further systematic studies will be necessary to deconvolute the influences of metal identity, ligand, solvent, additives, nucleophilic coupling partner, and other factors on chemoselectivity.

Soft templating: Nitrogen‐doped mesoporous carbon nanosphere (NMCS) with tunable sizes and uniform mesoporosity is synthesized by a facile soft‐templating method, whereby F127 (PEO–PPO–PEO triblock copolymer) can be used not only as a soft template to generate the mesostructure but also as a size‐control agent to tailor the size of NMCS ranging from 100 to 700 nm.

Abstract

Nitrogen‐doped mesoporous carbon nanosphere (NMCS) with tunable sizes and uniform mesoporosity was synthesized by a facile soft‐templating method. During the synthesis, F127 (PEO–PPO–PEO triblock copolymer) could be used not only as a soft template to generate the mesostructure but also as a size‐control agent to tailor the size of NMCS in a relatively wide range of 100 to 700 nm. In addition, the synthesis process was simple and suitable for large‐scale production. Moreover, the NMCS was used as support of ultrafine Ru nanoparticles (Ru/NMCS), which exhibited good catalytic performances for selective hydrogenation of quinolones. It is expected that the simple synthetic strategy for the NMCS can generate extensive interest in many catalysis and sorption applications.

Synthesis
DOI: 10.1055/s-0040-1705970

We herein describe the two-step synthesis of 6-adamantyl-2-pyridone from 1-acetyladamantane. The borane complex derived from 6-adamantyl-2-pyridone and the Piers borane liberates dihydrogen at 60 °C. The reverse reaction, hydrogen activation by the formed pyridonate borane is accomplished under mild conditions. The mechanism of the hydrogen activation is studied by DFT computations.
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Georg Thieme Verlag KG Rüdigerstraße 14, 70469 Stuttgart, Germany

Article in Thieme eJournals:
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