Ligand-Promoted Iridium-Catalyzed Transfer Hydrogenation of Terminal Alkynes with Ethanol and Its Application

Tetraethylammonium Salts as Solid, Easy to Handle Ethylene Precursors and Their Application in Mizoroki-Heck Coupling

In this study, we introduce a convenient Heck vinylation protocol that eliminates the requirement for ethylene gas as a coupling partner. In contrast to traditional methodologies, quaternary ammonium salts can serve as solid olefin precursors under ambient atmosphere conditions. The practicality of this method, distinguished by its convenience and safety in a one-pot reaction, renders it appealing for applications in research and discovery context.

Design, synthesis and biological evaluation of Nrf2 modulators for the treatment of glioblastoma multiforme

Glioblastoma multiforme (GBM) is a prevalent primary brain tumor. However, no specific therapeutic drug has been developed for it. Nuclear factor erythroid 2-related factor 2 (Nrf2) is a crucial transcription factor involved in the cellular response to oxidative stress. Numerous studies have demonstrated that Nrf2 plays a pivotal role in GBM angiogenesis, and inhibiting Nrf2 can significantly enhance patient prognosis. Using virtual screening technology, we examined our in-house library and identified pinosylvin as a potential compound with high activity. Pinosylvin exhibited robust hydrogen bond and Π-Π interaction with Nrf2. Cell experiments revealed that pinosylvin effectively reduced the proliferation of U87 tumor cells by regulating Nrf2 and demonstrated greater inhibitory activity than temozolomide. Consequently, we believe that this study will offer valuable guidance for the future development of highly efficient therapeutic drugs for GBM.

Classics in Chemical Neuroscience: Selegiline, Isocarboxazid, Phenelzine, and Tranylcypromine

The discovery of monoamine oxidase inhibitors (MAOIs) in the 1950s marked a significant breakthrough in medicine, creating a powerful new category of drug: the antidepressant. In the years and decades that followed, MAOIs have been used in the treatment of several pathologies including Parkinson's disease, Alzheimer's disease, and various cancers and as anti-inflammatory agents. Despite once enjoying widespread use, MAOIs have dwindled in popularity due to side effects, food-drug interactions, and the introduction of other antidepressant drug classes such as tricyclic antidepressants (TCAs) and selective serotonin reuptake inhibitors (SSRIs). The recently published prescriber's guide for the use of MAOIs in treating depression has kindled a resurgence of their use in the clinical space. It is therefore timely to review key aspects of the four "classic" MAOIs: high-dose selegiline, isocarboxazid, phenelzine, and tranylcypromine. This review discusses their chemical synthesis, metabolism, pharmacology, adverse effects, and the history and importance of these drugs within the broader field of chemical neuroscience.

Structural snapshots of an Al-Cu bond-mediated transformation of terminal acetylenes

The copper(i) alumanyl derivative, [{SiN^Dipp}Al-Cu(NHC^iPr)] (SiN^Dipp = {CH₂SiMe₂NDipp}₂; Dipp = 2,6-di-isopropylphenyl; NHC^iPr = N,N'-di-isopropyl-4,5-dimethyl-2-ylidene), reacts in a stepwise fashion with up to three equivalents of various terminal alkynes. This reactivity results in the sequential formation of cuprous (hydrido)(alkynyl)aluminate, (alkenyl)(alkynyl)aluminate and bis(alkynyl)aluminate derivatives, examples of which have been fully characterised. The process of alkene liberation resulting from the latter reaction step constitutes a unique case of alkyne transfer semi-hydrogenation in which the C-H acidic alkyne itself acts as a source of proton, with the Cu-Al bond providing the requisite electrons to effect reduction. This reaction sequence is validated by DFT calculations, which rationalise the variable stability of the initially formed heterobimetallic hydrides.

Palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor

A ligand-promoted, palladium-catalyzed transfer hydrogenation of terminal alkynes using ethanol as the hydrogen donor is developed. The chemical selectivity control is achieved based on ligand regulation. The use of triethanolamine and tetrahydrofuran at 80 °C under N2 is found to be critical for the transfer hydrogenation of terminal alkynes. The general applicability of this procedure is highlighted by the synthesis of 27 terminal alkenes in moderate to good yields.

E-Selective Manganese-Catalyzed Semihydrogenation of Alkynes with H2 Directly Employed or In Situ-Generated

Selective semihydrogenation of alkynes with the Mn(I) alkyl catalyst fac-[Mn(dippe)(CO)₃(CH₂CH₂CH₃)] (dippe = 1,2-bis(di-iso-propylphosphino)ethane) as a precatalyst is described. The required hydrogen gas is either directly employed or in situ-generated upon alcoholysis of KBH₄ with methanol. A series of aryl-aryl, aryl-alkyl, alkyl-alkyl, and terminal alkynes was readily hydrogenated to yield E-alkenes in good to excellent isolated yields. The reaction proceeds at 60 °C for directly employed hydrogen or at 60-90 °C with in situ-generated hydrogen and catalyst loadings of 0.5-2 mol %. The implemented protocol tolerates a variety of electron-donating and electron-withdrawing functional groups, including halides, phenols, nitriles, unprotected amines, and heterocycles. The reaction can be upscaled to the gram scale. Mechanistic investigations, including deuterium-labeling studies and density functional theory (DFT) calculations, were undertaken to provide a reasonable reaction mechanism, showing that initially formed Z-isomer undergoes fast isomerization to afford the thermodynamically more stable E-isomer.

Palladium-Catalyzed Semihydrogenation of Alkynes with EtOH: Highly Stereoselective Synthesis of E- and Z-Alkenes

A palladium-catalyzed semihydrogenation of alkynes to E- and Z-alkenes employing EtOH as the hydrogenating agent is reported. The selectivity of the reaction system was effectively controlled by ­ligand/additive and solvent regulation. The use of sodium acetate/­triethanolamine (NaOAc/TEOA), THF, and (1R,2R)-bis[(2-­methoxyphenyl)phenylphosphino]ethane [(R,R)-DIPAMP] in CH3CN was critical for the stereoselective semihydrogenation of alkynes. The general applicability of this procedure was highlighted by the synthesis of more than 36 alkenes, in good yields with high stereoselectivities.

Transfer hydrogenation of pyridinium and quinolinium species using ethanol as a hydrogen source to access saturated N-heterocycles

Catalytic transfer hydrogenation (TH) for the reduction of heterocycles is an emerging strategy for accessing biologically active saturated N-heterocycles. Herein, we report a TH protocol that utilizes ethanol as a...

Manganese-catalyzed transfer semihydrogenation of internal alkynes to E-alkenes with iPrOH as hydrogen source

The Mn-catalyzed transfer semihydrogenation of internal alkynes to E-alkenes is reported herein, along with Mn-catalyzed hydration of α-keto alkynes. Mechanistic studies displayed an asymmetrical Mn-hydride species performing the catalytic turnover.

Donor-Acceptor Bicyclopropyls as 1,6-Zwitterionic Intermediates: Synthesis and Reactions with 4-Phenyl-1,2,4-triazoline-3,5-dione and Terminal Acetylenes

The bicyclopropyl system activated by incorporation of donor and acceptor groups in the presence of Lewis acids was used as a synthetic equivalent of 1,6-zwitterions. Opening of both cyclopropane rings in 2'-aryl-1,1'-bicyclopropyl-2,2-dicarboxylates (D-A bicyclopropyl, ABCDs) in the presence of GaI₃ + Bu₄N⁺GaI₄^- results in 5-iodo-5-arylpent-2-enylmalonates as products of HI formal 1,6-addition to the bicyclopropyl system. The use of GaCl₃ or GaBr₃ as a Lewis acid and terminal aryl or alkyl acetylenes as 1,6-zwitterion interceptors allows the alkyl substituent to be grown to give the corresponding acyclic 7-chloro(bromo)-hepta-2,6-dienylmalonates. The reaction of ABCDs with 4-phenyl-1,2,4-triazoline-3,5-dione (PTAD) catalyzed by Yb(OTf)₃ also results in the opening of both cyclopropane rings. The reaction products are tetrahydropyridazine derivatives - (7,9-dioxo-1,6,8-triazabicyclo[4.3.0]non-3-en-2-ylmethyl)malonates - containing one more PTAD moiety in the malonyl group.

Homogeneous catalytic transfer semihydrogenation of alkynes – an overview of hydrogen sources, catalysts and reaction mechanisms

Chemoselective semihydrogenation of alkynes to alkenes with E- or Z-stereoselectivity is among the most important transformations in the synthesis of highly functional organic building blocks.