Reformatsky Reaction Research Articles

Chromium Catalyzed Asymmetric Reformatsky Reaction

AbstractThis study describes an unprecedented chromium‐catalyzed asymmetric Reformatsky reaction, enabling the synthesis of chiral β‐hydroxy carbonyl compounds from α‐chlorinated or α‐brominated esters and amides. By employing a chiral chromium/diarylamine bis(oxazoline) catalyst, we achieved relatively broad functional group tolerance. Distinct from known reports, the protocol operates under both classical and photoredox conditions, facilitated by the in situ formation of a nucleophilic chiral chromium intermediate through a radical‐polar crossover mechanism. Preliminary mechanistic insights, supported by DFT calculations, identify the nucleophilic aldehyde addition as the key stereo‐determining step. This approach not only overcomes the limitations of existing Reformatsky reactions but also provides a versatile strategy for accessing complex chiral molecules.

Chromium Catalyzed Asymmetric Reformatsky Reaction.

This study describes an unprecedented chromium-catalyzed asymmetric Reformatsky reaction, enabling the synthesis of chiral β-hydroxy carbonyl compounds from α-chlorinated or α-brominated esters and amides. By employing a chiral chromium/diarylamine bis(oxazoline) catalyst, we achieved relatively broad functional group tolerance. Distinct from known reports, the protocol operates under both classical and photoredox conditions, facilitated by the in situ formation of a nucleophilic chiral chromium intermediate through a radical-polar crossover mechanism. Preliminary mechanistic insights, supported by DFT calculations, identify the nucleophilic aldehyde addition as the key stereo-determining step. This approach not only overcomes the limitations of existing Reformatsky reactions but also provides a versatile strategy for accessing complex chiral molecules.

High Degree of Chemoselectivities Recorded during the Reformatsky Reaction on Coumarinyl phenyl ketones and Formyl Coumarins

High Degree of Chemoselectivities Recorded during the Reformatsky Reaction on Coumarinyl phenyl ketones and Formyl Coumarins

An Update on Recent Green Synthetic Approaches to Coumarins

Abstract: Coumarin and its derivatives are privileged heterocyclic motifs and important building blocks for developing the biologically active compound due to its significant role in the development of new drugs. As a result, many methodologies have been developed to synthesize this important class of compounds. However, some methods are associated with toxic and corrosive catalysts, longer reaction time, poor yield, less purity, and by-products along with the desired product. In order to minimize the utilization and generation of toxic organic substances, green synthetic methods are applied in this manner. Green chemistry methods cover a wide range of methods, including the application of ultrasound and microwaves, ionic liquids and deep eutectic solvents, solvent-free and catalyst-free synthesis, and mechanosynthesis. These green synthetic methods have successfully performed all typical condensation reactions for coumarin synthesis like Knoevenagel, Perkin, Kostanecki-Robinson, Pechmann, and Reformatsky reactions. Compared to conventional methods, these methods not only minimize the use and generation of harmful chemicals but also improve reaction efficiency in terms of product yields, purity, energy consumption, and post-synthetic procedures. Due to the implication of coumarin (2-oxo-2H-1-benzopyran) backbone as a biologically active ubiquitous fragment and the recent demands of reducing toxic solvents, catalysts, and energy consumption, this review summarized various green synthetic methods for coumarin synthesis. Moreover, researchers working on this coumarin scaffold synthesis can find handy information from this review on the green synthetic approaches to their synthesis.

The Tungsten-Promoted Synthesis of Piperidyl-Modified erythro-Methylphenidate Derivatives.

Due to its efficacy as a dopamine receptor agonist, methylphenidate (MPH) is of interest as a potential therapeutic for cocaine addiction. While numerous derivatives of MPH have been investigated for their potential medicinal value, functionalization of the piperidine ring has not been explored. The pyridine borane ligand in WTp(NO)(PMe3)(η2-pyBH3) is dearomatized by the metal and can be elaborated to the analogous η2-mesylpyridinium complex. Installing a methyl phenylacetate moiety at the C2' position via a Reformatsky reaction followed by a tandem protonation/nucleophilic addition sequence results in a library of erythro MPH analogues functionalized at the piperidyl C5' position. The functional group is added chemoselectively to C5', cis to the methyl phenylacetate. Repeating this procedure with an enantioenriched source of the tungsten reagent results in enantioenriched MPH derivatives. All identities of the newly reported compounds are supported by comprehensive 2D NMR and HRMS data or crystallographic data.

Asymmetric Total Syntheses of Macroline-Type Alkaloids Alstomicine and Alstofolinine A

AbstractMacroline-type monoterpenoid indole alkaloids represent a fascinating class of natural products with polycyclic structures, diverse biological and pharmacological activities. Herein the asymmetric total syntheses of two of this type alkaloids, (–)-Alstomicine and (–)-Alstofolinine A are reported. Notably, these two alkaloids are divergently synthesized from a common indole-fused azabicyclo[3.3.1]nonane intermediate, which was easily obtained via a Mannich-type cyclization. An SmI2-mediated Reformatsky reaction and a Pd-catalyzed carbonylative lactonization are employed to construct the lactone moieties presented in Alstomicine and Alstofolinine A, respectively.

Iron-mediated Reformatsky reaction of iododifluoromethyl ketones with aldehydes: Preparation of α,α-difluoro-β-hydroxyketone derivatives

The α,α-difluoro-β-hydroxyketone skeleton is an important pharmacodynamic structure in the synthesis study of pharmaceuticals. Herein, we describe a novel iron mediated Reformatsky reaction of iododifluoroacetophenones with aldehydes, which offers a relatively more economical and environment friendly route for the construction of α,α-difluoro-β‑hydroxyl ketone with good yield. In addition, iron shows wider applicability compared with other metals. It can mediate the reaction between iodifluorophenone and α,β-unsaturated ketones or sulfonimides, obtaining 1,2-addition products and α,α-difluoro-β-aminone compounds, respectively.

Photoinduced reductive Reformatsky reaction of α-haloesters and aldehydes or ketones by cooperative dual-metal catalysis.

A photoinduced reductive Reformatsky reaction by cooperative dual-metal catalysis is described. This methodology enables the implementation of this venerable reaction in environmentally friendly conditions, obviating the need for a stoichiometric amount of metals. A broad range of synthetically useful β-hydroxy esters can be efficiently prepared in moderate to high yields using this protocol.

Synthesis, Characterisation and Mechanism of Action of Anticancer 3-Fluoroazetidin-2-ones.

The stilbene combretastatin A-4 (CA-4) is a potent microtubule-disrupting agent interacting at the colchicine-binding site of tubulin. In the present work, the synthesis, characterisation and mechanism of action of a series of 3-fluoro and 3,3-difluoro substituted β-lactams as analogues of the tubulin-targeting agent CA-4 are described. The synthesis was achieved by a convenient microwave-assisted Reformatsky reaction and is the first report of 3-fluoro and 3,3-difluoro β-lactams as CA-4 analogues. The β-lactam compounds 3-fluoro-4-(3-hydroxy-4-methoxyphenyl)-1-(3,4,5-trimethoxy phenyl)azetidin-2-one 32 and 3-fluoro-4-(3-fluoro-4-methoxyphenyl)-1-(3,4,5-trimethoxyphenyl)azetidin-2-one) 33 exhibited potent activity in MCF-7 human breast cancer cells with IC50 values of 0.075 µM and 0.095 µM, respectively, and demonstrated low toxicity in non-cancerous cells. Compound 32 also demonstrated significant antiproliferative activity at nanomolar concentrations in the triple-negative breast cancer cell line Hs578T (IC50 0.033 μM), together with potency in the invasive isogenic subclone Hs578Ts(i)8 (IC50 = 0.065 μM), while 33 was also effective in MDA-MB-231 cells (IC50 0.620 μM). Mechanistic studies demonstrated that 33 inhibited tubulin polymerisation, induced apoptosis in MCF-7 cells, and induced a downregulation in the expression of anti-apoptotic Bcl2 and survivin with corresponding upregulation in the expression of pro-apoptotic Bax. In silico studies indicated the interaction of the compounds with the colchicine-binding site, demonstrating the potential for further developing novel cancer therapeutics as microtubule-targeting agents.

Difluoroalkylation of Tertiary Amides and Lactams by an Iridium-Catalyzed Reductive Reformatsky Reaction.

An iridium-catalyzed, reductive alkylation of abundant tertiary lactams and amides using 1–2 mol % of Vaska’s complex (IrCl(CO)(PPh3)2), tetramethyldisiloxane (TMDS), and difluoro-Reformatsky reagents (BrZnCF2R) for the general synthesis of medicinally relevant α-difluoroalkylated tertiary amines is described. A broad scope (46 examples), including N-aryl- and N-heteroaryl-substituted lactams, demonstrated an excellent functional group tolerance. Furthermore, late-stage drug functionalizations, a gram-scale synthesis, and common downstream transformations proved the potential synthetic relevance of this new methodology.

Exploration of Oxidative Ritter-Type Reaction of α-Arylketones and Its Application for the Collective Total Syntheses of Erythrina Alkaloids

Exploration of Oxidative Ritter-Type Reaction of α-Arylketones and Its Application for the Collective Total Syntheses of <i>Erythrina</i> Alkaloids

Indium-Mediated Reformatsky Reaction of Iododifluoro Ketones with Aldehydes: Preparation of α,α-Difluoro-β-hydroxyketone Derivatives in Water

AbstractIndium can efficiently mediate the Reformatsky reaction of iododifluoroacetylketones with aldehydes to afford the corresponding α,α-difluoro-β-hydroxyketones in high yield in pure water This reaction has excellent substrate suitability and functional group selectivity and provides an efficient approach for the synthesis of bioactive molecules containing the α,α-difluoro-β-hydroxyketone pharmacophore.

Stereoselective Synthesis of β-C-Glycosides of 3-Deoxy-d-manno-oct-2-ulosonic Acid (Kdo) via SmI2-Mediated Reformatsky Reactions.

An efficient and simple approach for stereoselective synthesis of β-Kdo C-glycosides was described, which relies on easily available peracetylated anomeric acetate or anomeric 2-pyridyl sulfide to couple with carbonyl compounds via SmI2-mediated Reformatsky reactions. The utility of this methodology is exemplified by the streamlined synthesis of a practical β-Kdo C-glycoside with an anomeric aminopropyl linker to conjugate with other biomolecules for further biological studies.

Manganese-Mediated Reformatsky Reaction: Highly Divergent Synthesis ofβ-Hydroxyalkanoates

Manganese-Mediated Reformatsky Reaction: Highly Divergent Synthesis of<i>β</i>-Hydroxyalkanoates

Strategies for the Photocatalytic Generation of Carbanion Equivalents for Reductant-Free C-C Bond Formations.

ConspectusThe use of photocatalysis in organic chemistry has encountered a surge of novel transformations since the start of the 21st century. The majority of these transformations are driven by the generation and subsequent reaction of radicals, owing to the intrinsic property of common photocatalysts to transfer single electrons from their excited state. While this is a powerful and elegant method to develop novel transformations, several research groups recently sought to further extend the toolbox of photocatalysis into the realm of polar ionic reactivity by the formation of cationic as well as anionic key reaction intermediates to furnish a desired product.Our group became especially interested in the photocatalytic formation of anionic carbon nucleophiles, as the overall transformation resembles classical organometallic reactions like Grignard, Barbier, and Reformatsky reactions, which are ubiquitous in organic synthesis with broad applications especially in the formation of valuable C–C bonds. Although these classical reactions are frequently applied, their use still bears certain disadvantages; one is the necessity of an (over)stoichiometric amount of a reducing metal. The reducing, low-valent, metal is solely applied to activate the starting material to form the organometallic carbanion synthon, while the final reaction product does generally not contain a metal species. Hence, a stoichiometric amount of metal salt is bound to be generated at the end of each reaction, diminishing the atom economy. The use of visible light as mild and traceless activation agent to drive chemical reactions can be a means to arrive at a more atom economic transformation, as a reducing metal source is avoided. Beyond this, the vast pool of photocatalytic activation methods offers the potential to employ easily available starting materials, as simple as unfunctionalized alkanes, to open novel and more facile retrosynthetic pathways. However, as mentioned above, photocatalysis is dominated by open-shell radical reactivity. With neutral radicals showing an intrinsically different reactivity than ionic species, novel strategies to form intermediates expressing a polar behavior need to be developed in order to achieve this goal.In the last couple of years, several methods toward this aim have been reported by our group and others. This Account aims to give an overview of the different existing strategies to photocatalytically form carbon centered anions or equivalents of those in order to form C–C bonds. As the main concept is to omit a stoichiometric reductant source (like a low-valent metal in classical organometallic reactions), only redox-neutral and reductant-free transformations were taken into closer consideration. We present selected examples of important strategies and try to illustrate the intentions and concepts behind the methods developed by our group and others.

Synthetic, Mechanistic, and Biological Interrogation of Ginkgo biloba Chemical Space En Route to (-)-Bilobalide.

Here we interrogate the structurally dense (1.64 mcbits/Å3) GABAA receptor antagonist bilobalide, intermediates en route to its synthesis, and related mechanistic questions. 13C isotope labeling identifies an unexpected bromine migration en route to an α-selective, catalytic asymmetric Reformatsky reaction, ruling out an asymmetric allylation pathway. Experiment and computation converge on the driving forces behind two surprising observations. First, an oxetane acetal persists in concentrated mineral acid (1.5 M DCl in THF-d8/D2O); its longevity is correlated to destabilizing steric clash between substituents upon ring-opening. Second, a regioselective oxidation of des-hydroxybilobalide is found to rely on lactone acidification through lone-pair delocalization, which leads to extremely rapid intermolecular enolate equilibration. We also establish equivalent effects of (-)-bilobalide and the nonconvulsive sesquiterpene (-)-jiadifenolide on action potential-independent inhibitory currents at GABAergic synapses, using (+)-bilobalide as a negative control. The high information density of bilobalide distinguishes it from other scaffolds and may characterize natural product (NP) space more generally. Therefore, we also include a Python script to quickly (ca. 132 000 molecules/min) calculate information content (Böttcher scores), which may prove helpful to identify important features of NP space.

Natural and Synthetic Spirobutenolides and Spirobutyrolactones

AbstractSpirobutenolides and spirobutyrolactones structural motifs are widespread in various natural products that exhibit a broad array of biological activities. Additionally, their synthetic analogues also serve as biologically active compounds and building blocks of complex molecules. Owing to the wide range of pharmacological activities and structural diversity of the spirobutenolides and spirobutyrolactones, various efficient synthetic methodologies have been established to construct such interesting scaffolds. In the past decades, numerous total syntheses of spirobutenolides and spirobutyrolactones containing natural products have been reported. Structurally diverse spirobutenolides and spirobutyrolactones have been synthesized by using singlet oxygen, Mannich reaction, aldol condensation, rearrangement reaction, Reformatsky reaction, Michael‐addition cyclization, Diels‐Alder reaction, photocyclization reaction, and pericyclic reactions. Recently, metal‐catalyzed cyclization, photocatalyzed radical cyclization, Baylis‐Hillman reaction, asymmetric organocatalysis, NHC catalysis, ring contraction reactions, and hypervalent iodine catalysis have emerged as powerful tools to architect these nuclei. This review gives an overview of advancements in chemically and biologically relevant spirobutenolides and spirobutyrolactones of natural and synthetic origin. It also covers the newer methodologies for the construction of natural as well as synthetic spirobutenolides and spirobutyrolactones along with their potential applications.

Enantioselective Reformatsky Reaction of Ketones Catalyzed by Chiral Indolinylmethanol

A reliable and practical Reformatsky reaction of ethyl iodide acetate with ketones for the synthesis of chiral β‐hydroxyl carbonyl compounds in good yields and excellent enantioselectivities is presented. A readily available dihydroindole derivative was used as chiral catalyst, ethyl iodide acetate was the nucleophile, and Me2Zn was the zinc source. The presence of air was found to be essential for the efficient construction of new carbon–carbon bonds through a radical pathway.

Highly Catalytic Enantioselective Reformatsky Reaction with Aldehydes and Ketones Using an Available Prolinol Ligand.

A highly Me2Zn-mediated catalytic enantioselective Reformatsky reaction of aldehydes and ketones with ethyl iodoacetate using a readily available prolinol ligand is reported. This reaction provides an efficient method for the construction of β-hydroxy esters in up to 98% yield and 95% enantiomeric excess (ee) value. A wide range of functional groups are tolerated and the practicality of this protocol is demonstrated by performing the reaction on a gram scale.

Reformatsky Reaction of Methyl 1-Bromocyclohexanecarboxylate with N,N′-(1,4-Phenylene)bis(1-arylmethanimines)

Reformatsky reagent prepared from methyl 1-bromocyclohexanecarboxylate reacted with N,N′-(1,4-phenylene)bis(1-arylmethanimines) to produce 2,2′-(1,4-phenylene)bis[3-aryl-2-azaspiro[3.5]nonan-1-ones] as a result of successive nucleophilic additions to the C=N double bonds of the substrate and intramolecular cyclization of the corresponding intermediates. The stepwise reaction mechanism was proved by the isolation of 2-[4-(arylmethylideneamino)phenyl]-3-aryl-2-azaspiro[3.5]nonan-1-ones in the reactions with equimolar amounts of the Schiff base and Reformatsky reagent.