Search

Birch reactions employing alkali metals in ammonia have been a well‐established method for the reduction and functionalisation of aromatic compounds for nearly 100 years. Speculations regarding intermediates in the reaction pathway have been discussed since the beginning. We hereby report the isolation of NMe4(HNaph) (1), a kinetically trapped intermediate of the Birch reaction of naphthalene and sodium in liquid ammonia. 1 has been fully characterised and has been shown to continue to react to 1,2/1,4‐dihydronaphthalene – the Birch product of the reduction of naphthalene. The reactivity of 1 was investigated towards activity as an electron and hydride transfer agent with both, elements and small organic molecules. 1 demonstrates a tamed reduction potential which allows for controlled reactions such as the selective formation of hexasulphide and hexaselenide anions. [ABSTRACT FROM AUTHOR]

Birch reductions are well‐known transformations of arenes, applied for large scale synthesis of 1,4‐cyclohexadienes. Herein, we describe first reactions of benzoic acids in the presence of carbonyl compounds, affording aldol products in moderate to high yields. Alkyl aldehydes give the expected nonconjugated dienes by reaction at the α‐position. Interestingly, the intermediately formed enolate attacks aryl aldehydes and ketones from its γ‐position, which can be explained by steric hindrance. This opens the door for the one‐pot synthesis of 1,3‐cyclohexadienes, which are not accessible by classical Birch reductions. Our method is applicable to benzoic, m‐ and p‐toluic acid and various carbonyl compounds, and more than 25 new products were isolated in up to 93 % yield. Prochiral aryl aldehydes afford diastereomeric mixtures in ratios of about 4 : 1, but in the cyclohexadiene ring only trans isomers are formed with high selectivity. Finally, the 1,3‐cyclohexadienes are suitable precursors for further transformations, which we have demonstrated in first examples. Thus, aromatization affords products of a formal meta selective Friedel–Crafts alkylation, and four new stereocenters were generated by cycloaddition of singlet oxygen with excellent selectivity. [ABSTRACT FROM AUTHOR]

This document provides information on the synthesis of the dopamine agonist Rotigotine, which is used to treat Parkinson's disease and restless leg syndrome. The authors discuss different synthetic approaches and successfully synthesized Rotigotine using reductive amination with a high yield. The document also includes information on the synthesis and characterization of three compounds related to Rotigotine, along with their spectral data. Additionally, it provides details on the synthesis and chiral separation of (±)-Rotigotine, including its chemical structure, physical properties, and analytical data. The authors acknowledge Chemveda Life Sciences for their assistance in the separation process. [Extracted from the article]

α,β-Doymamış karbonil bileşikleri olan iki asit, bir ester ve bir kalkon bileşikleri farklı şartlarda Birch indirgemeleri incelendi. Ayrıca, gerilimli izole çift bağlar içeren norbornadien ve benzonorbornadien bileşiklerinin de farklı şartlarda Birch indirgemeleri incelendi.

In this contribution, we present "Birch‐type", and other reductions of simple arenes by the potassium salt of an anionic magnesium dinitrogen complex, [{K(TCHPNON)Mg}2(μ‐N2)] (TCHPNON=4,5‐bis(2,4,6‐tricyclohexylanilido)‐2,7‐diethyl‐9,9‐dimethyl‐xanthene), which acts as a masked dimagnesium(I) diradical in these reactions. This reagent is non‐hazardous, easy‐to‐handle, and in some cases provides access to 1,4‐cyclohexadiene reduction products under relatively mild reaction conditions. This system works effectively to reduce benzene, naphthalene and anthracene through magnesium‐bound "Birch‐type" reduction intermediates. Cyclohexadiene products can be subsequently released from the magnesium centres by protonolysis with methanol. In contrast, the reduction of substituted arenes is less selective and involves competing reaction pathways. For toluene and 1,3,5‐triphenylbenzene, the structural authentication of "Birch‐type" reduction intermediates is conclusive, although the formation of corresponding 1,4‐cyclohexadiene derivatives was low yielding. Reduction of anisole did not yield an isolable "Birch‐type" intermediate, but instead gave a C−O activation product. Treating triphenylphosphine with [{K(TCHPNON)Mg}2(μ‐N2)] resulted in the extrusion of both biphenyl and dinitrogen to afford a magnesium(II) phosphanide [{K(TCHPNON)Mg(μ‐PPh2)}2]. Reduction of fluorobenzene proceeded via C−F activation of the arene, and isolation of the magnesium(II) fluoride [{K(TCHPNON)Mg(μ‐F)}2]. Finally, the two‐electron reduction of 1,3,5,7‐cyclooctatetraene (COT) with [{K(TCHPNON)Mg}2(μ‐N2)] yielded a complex, [{K(TCHPNON)Mg}2(μ‐COT)], incorporating the aromatic dianion (COT2−). [ABSTRACT FROM AUTHOR]

Dearomative partial reduction is an extraordinary approach for transforming benzenoid arenes and has been well‐known for many decades, as exemplified by the dehydrogenation of Birch reduction and the hydroarylation of Crich addition. Despite its remarkable importance in synthesis, this field has experienced slow progress over the last half‐century. However, a revival has been observed with the recent introduction of electrochemical and photochemical methods. In this Minireview, we summarize the recent advancements in dearomative partial reduction of benzenoid arenes, including dihydrogenation, hydroalkylation, arylation, alkenylation, amination, borylation and others. Further, the intriguing utilization of dearomative partial reduction in the synthesis of natural products is also emphasized. It is anticipated that this Minireview will stimulate further progress in arene dearomative transformations. [ABSTRACT FROM AUTHOR]

Birch reduction and similar dissolved metal‐type transformations hold significant importance in the organic synthesis toolbox. Historically, the field has been dominated by alkali metal reductants. In this study, we report that largely neglected, low‐reactive alkaline earth metals can become powerful and affordable reductants when used in a ball mill under essentially solvent‐free conditions, in the presence of ethylenediamine and THF as liquid additives. Calcium can reduce both electron‐deficient and electron‐rich arenes, with yields of products similar to those obtained with lithium metal. Magnesium reveals enhanced reducing power, enabling the reduction of benzoic acids while keeping electron‐rich aromatic moieties intact and allows for chemoselective transformations. The developed mechanochemical approach uses readily available and safer‐to‐handle metals, operates under air and ambient temperature conditions, and can be used for gram‐scale preparations. Finally, we demonstrate that the developed conditions can be used for other dissolved metal‐type reductive transformations, including reductive amination, deoxygenation, dehalogenation, alkene and alkyne reductions. [ABSTRACT FROM AUTHOR]

In this study, we report a mechanochemical protocol for highly efficient and air-tolerant calcium-based Birch reduction. The developed mechanochemical approach allows the use of readily available calcium metal as a safer-to-handle reductant for Birch reduction of various aromatic compounds. The reaction was rapid and the desired dearomatization products were obtained in good yields within 15 min at ambient temperature. Notably, all synthetic operations can be performed under ambient conditions without a complicated reaction setup involving inert gases. The feasibility of the gram-scale synthesis was demonstrated, further highlighting the practical utility of this protocol. [ABSTRACT FROM AUTHOR]

Group 1 elements exhibit the lowest electronegativity values in the Periodic Table. The chemical reduction of Group 1 metal cations M+ to M(0) is extremely challenging. Common tetraaryl borates demonstrate limited redox properties and are prone to decomposition upon oxidation. In this study, by employing simple yet versatile bipyridines as ligands, we synthesized a series of redox-active borate anions characterized by NMR and X-ray single-crystal diffraction. Notably, the borate anion can realize the reduction of Li+, generating elemental lithium metal and boron radical, thereby demonstrating its potent reducing ability. Furthermore, it can serve as a powerful two-electron-reducing reagent and be readily applied in various reductive homo-coupling reactions and Birch reduction of acridine. Additionally, this borate anion demonstrates its catalytic ability in the selective two-electron reduction of CO2 into CO. Chemical reduction of alkali cations to their metals is extremely challenging. Here, the authors synthesized a series of redox-active borate anions stabilized by bipyridine ligands which can reduce lithium ions generating elemental lithium metal and borate radicals. [ABSTRACT FROM AUTHOR]

Cyclohexane (CHA), cyclohexene (CHE), and 1,4-cyclohexadiene (CHD) derivatives have a wide variety of applications and scope in synthetic and industrial organic chemistry. These cyclic hydrocarbons are found in a variety of natural products, including herbal plants and fruits as basic fragrance components. The extraction and isolation of these essential hydrocarbons are too complex and difficult to pursue. However, the reduction of benzene and its derivatives is an essential and effective approach for producing CHA, CHE, and CHD derivatives. To obtain CHA, CHE, and CHD derivatives, several types of reduction techniques for benzene and its derivatives have been developed over the years, including various forms of catalytic hydrogenation, Benkeser reduction, classic and many modified Birch reductions such as ammonia-free, metal-free photochemical, solvent-free, electrochemical and electride-mediated Birch reduction. In this study, the comparison of chemoselectivity, regioselectivity, reaction conditions, reduction efficiency, and environmentally acceptable approaches of these techniques used for benzene reduction are summarized. [ABSTRACT FROM AUTHOR]

Routes to the framework of perylenequinone‐derived mycotoxins of the dihydroanthracene type are described. Starting with anthracene derivatives, attachment of C3 units at positions 9 and 10 and twofold cyclization would furnish the required pentacycle. Heck‐type couplings, SN2 additions of enolates, alkynyl and allyl additions turned out to be not successful, while addition of a Grignard reagent prepared from acetal‐protected 3‐bromopropionaldehyde to anthraflavic acid methyl ester, subsequent acetal cleavage, and Birch reduction furnished octahydroperylene in only four steps. [ABSTRACT FROM AUTHOR]

An established concept to create radical intermediates is photoexcitation of a catalyst to a higher energy intermediate, subsequently leading to a photoinduced electron transfer (PET) with a reaction partner. The known concept of consecutive photoinduced electron transfer (con-PET) leads to catalytically active species even higher in energy by the uptake of two photons. Generally speaking, increased photon uptake leads to a more potent reductant. Here, we report the concept of multi-photoinduced electron transfer catalysis (>2 photons), termed multi-PET, which is enabled by photoinduced one-electron reductions of an organic dye. Further irradiation of the doubly reduced species leads to a photoexcited dianionic super-reductant, which is more potent than Li metal - one of the strongest chemical reductants known. This multi-photon process which is enabled by 390 nm LEDs allows the cleavage of strong carbon-fluorine bonds and reduction of other halides even in very electron-rich substrates. The resulting radicals are quenched by hydrogen atoms or engaged in carbon-carbon and carbon-phosphorus bond formations, highlighting the utility of multi-PET for organic chemistry. In addition, multi-PET enabled Birch-type reductions. Spectroscopic, chemical and computational investigations are presented to gain mechanistic insights., (© 2024 Wiley‐VCH GmbH.)

This article discusses the advances in electrosynthesis for a greener chemical industry. It highlights the potential of renewable electricity in powering chemical plants and driving thermocatalytic processes, as well as its role in reducing the environmental footprint of the chemical industry. Electrosynthesis, which uses electrons as an energy source and green reagent, offers opportunities for increased selectivity, green reaction pathways, and reduced chemical waste. The article also explores the modular nature of electrochemical reactors and their suitability for distributed chemical manufacturing. Various studies on electrosynthesis and electrochemical manufacturing are presented, including their applications in the production of green hydrogen, ammonia, hydrogen peroxide, and commodity chemicals. The article concludes by discussing the importance of electrosynthesis in environmental remediation, waste treatment, and computational methods for chemical transformation. [Extracted from the article]