C-C fragmentation: origins and recent applications

Type I [4σ+4π] versus [4σ+4π-1] Cycloaddition To Access Medium-Sized Carbocycles and Discovery of a Liver X Receptor β-Selective Ligand

Transition-metal-catalyzed [4+4] cycloaddition leading to cyclooctanoids has centered on dimerization between 1,3-diene-type substrates. Herein, we describe a [4σ+4π-1] and [4σ+4π] cycloaddition strategy to access 7/8-membered fused carbocycles through rhodium-catalyzed coupling between the 4σ-donor (benzocyclobutenones) and pendant diene (4π) motifs. The two pathways can be controlled by adjusting the solvated CO concentration. A broad range (>40 examples) of 5-6-7 and 5-6-8 polyfused carbocycles was obtained in good yields (up to 90 %). DFT calculations, kinetic monitoring and 13C-labeling experiments were carried out, suggesting a plausible mechanism. Notably, one 5-6-7 tricycle was found to be a very rare, potent, and selective ligand for the liver X receptor β (KD=0.64 μM), which is a potential therapeutic target for cholesterol-metabolism-related fatal diseases.

Electrochemical C-H/C-C Bond Oxygenation: A Potential Technology for Plastic Depolymerization

Herein, we provide eco-friendly and safely operated electrocatalytic methods for the selective oxidation directly or with water, air, light, metal catalyst or other mediators serving as the only oxygen supply. Heavy metals, stoichiometric chemical oxidants, or harsh conditions were drawbacks of earlier oxidative cleavage techniques. It has recently come to light that a crucial stage in the deconstruction of plastic waste and the utilization of biomass is the selective activation of inert C(sp3 )-C/H(sp3 ) bonds, which continues to be a significant obstacle in the chemical upcycling of resistant polyolefin waste. An appealing alternative to chemical oxidations using oxygen and catalysts is direct or indirect electrochemical conversion. An essential transition in the chemical and pharmaceutical industries is the electrochemical oxidation of C-H/C-C bonds. In this review, we discuss cutting-edge approaches to chemically recycle commercial plastics and feasible C-C/C-H bonds oxygenation routes for industrial scale-up.

Electrochemical Radical Retro-Allylation of Homoallylic Alcohols with Sulfonyl Hydrazides

We report herein the first examples of electrochemical radical retro-allylation of homoallylic alcohols via the cleavage of the C(sp3)-C(sp3) bond. In this reaction, a variety of sulfonyl hydrazides were employed as the environmentally friendly radical sources via an electrochemical dehydrazination with the release of N2 and H2 as the byproducts, leading to sulfonyl allylic compounds in moderate to good yields. The reaction features metal- and base-free reaction conditions, broad functional group tolerance, and a broad substrate scope.

Carbon-Carbon Bond Cleavage for Late-Stage Functionalization

Late-stage functionalization (LSF) introduces functional group or structural modification at the final stage of the synthesis of natural products, drugs, and complex compounds. It is anticipated that late-stage functionalization would improve drug discovery's effectiveness and efficiency and hasten the creation of various chemical libraries. Consequently, late-stage functionalization of natural products is a productive technique to produce natural product derivatives, which significantly impacts chemical biology and drug development. Carbon-carbon bonds make up the fundamental framework of organic molecules. Compared with the carbon-carbon bond construction, the carbon-carbon bond activation can directly enable molecular editing (deletion, insertion, or modification of atoms or groups of atoms) and provide a more efficient and accurate synthetic strategy. However, the efficient and selective activation of unstrained carbon-carbon bonds is still one of the most challenging projects in organic synthesis. This review encompasses the strategies employed in recent years for carbon-carbon bond cleavage by explicitly focusing on their applicability in late-stage functionalization. This review expands the current discourse on carbon-carbon bond cleavage in late-stage functionalization reactions by providing a comprehensive overview of the selective cleavage of various types of carbon-carbon bonds. This includes C-C(sp), C-C(sp2), and C-C(sp3) single bonds; carbon-carbon double bonds; and carbon-carbon triple bonds, with a focus on catalysis by transition metals or organocatalysts. Additionally, specific topics, such as ring-opening processes involving carbon-carbon bond cleavage in three-, four-, five-, and six-membered rings, are discussed, and exemplar applications of these techniques are showcased in the context of complex bioactive molecules or drug discovery. This review aims to shed light on recent advancements in the field and propose potential avenues for future research in the realm of late-stage carbon-carbon bond functionalization.

Chemospecific C3- and C2-Olefinations of Isatins by TfOH-Promoted Tandem Aldol-Grob and Semiacetalization-Grob Fragmentations

A novel method for TfOH-promoted chemospecific C3- and C2-olefinations of isatins is developed, which offers the first examples of Grob fragmentation using isatins and amides as substrates.

Photoredox Cleavage of a Csp3-Csp3 Bond in Aromatic Hydrocarbons

Functionalizing molecules through the selective cleavage of carbon-carbon bonds is an attractive approach in synthetic chemistry. Despite recent advances in both transition-metal catalysis and radical chemistry, the selective cleavage of inert C_sp3-C_sp3 bonds in hydrocarbon feedstocks remains challenging. Examples reported in the literature typically involve substrates containing redox functional groups or highly strained molecules. In this article, we present a straightforward protocol for the cleavage and functionalization of C_sp3-C_sp3 bonds in alkylbenzenes using photoredox catalysis. Our method employs two distinct bond scission pathways. For substrates with tertiary benzylic substituents, a carbocation-coupled electron transfer mechanism is prevalent. For substrates with primary or secondary benzylic substituents, a triple single-electron oxidation cascade is applicable. Our strategy offers a practical means of cleaving inert C_sp3-C_sp3 bonds in molecules without any heteroatoms, resulting in primary, secondary, tertiary, and benzylic radical species.

A cheap metal catalyzed ring expansion/cross-coupling cascade: a new route to functionalized medium-sized and macrolactones

An efficient alkoxyl radical-triggered ring expansion/cross-coupling cascade was developed under cheap metal catalysis. Through the metal-catalyzed radical relay strategy, a wide range of medium-sized lactones (9-11 membered) and macrolactones (12, 13, 15, 18, and 19-membered) were constructed in moderate to good yields, along with diverse functional groups including CN, N3, SCN, and X groups installed concurrently. Density functional theory (DFT) calculations revealed that reductive elimination of the cycloalkyl-Cu(iii) species is a more favorable reaction pathway for the cross-coupling step. Based on the results of experiments and DFT, a Cu(i)/Cu(ii)/Cu(iii) catalytic cycle is proposed for this tandem reaction.

Aerobic C–C Bond Cleavage of Allylic Alcohols via Co-Catalyzed Hydrogen Atom Transfer

A simple, efficient method has been developed for the Co^III-H-catalyzed aerobic C-C bond cleavage of tertiary allylic alcohols to access ketones. This novel approach presents excellent chemoselectivity, good functional group compatibility, and high yields. This reaction occurs through a HAT-initiated peroxide intermediate, and an adjacent glycol-type diradical fragmentation process is recommended.

Decarboxylative oxidation-enabled consecutive C-C bond cleavage

The selective cleavage of C-C bonds is of fundamental interest because it provides an alternative approach to traditional chemical synthesis, which is focused primarily on building up molecular complexity. However, current C-C cleavage methods provide only limited opportunities. For example, selective C(sp3)-C(sp3) bond cleavage generally relies on the use of transition-metal to open strained ring systems or iminyl and alkoxy radicals to induce β-fragmentation. Here we show that by merging photoredox catalysis with copper catalysis, we are able to employ α-trisubstituted carboxylic acids as substrates and achieve consecutive C-C bond cleavage, resulting in the scission of the inert β-CH2 group. The key transformation relies on the decarboxylative oxidation process, which could selectively generate in-situ formed alkoxy radicals and trigger consecutive C-C bond cleavage. This complicated yet interesting reaction might help the development of other methods for inert C(sp3)-C(sp3) bond cleavage.

Iminologous epoxide ring-closure

The discovery of new reactions enables chemists to attain a better understanding of fundamental chemical reactivity and push the boundaries of organic synthesis. Our understanding and manipulation of high-energy states such as reactive conformations, intermediates, and transition structures contribute to this field. Herein we interrogate epoxide ring-closure by inserting the C[double bond, length as m-dash]N functionality into a well-known precursor to nucleophilic epoxide ring-closure. The synthesis of tetrasubstituted, nitrile-tethered epoxides takes place via activation of iminologous diols followed by fragmentation. Mechanistic study reveals the transformation to be stereospecific, which is consistent with the concerted nature of the epoxide ring-closure.

Metal-Free Catalysis in C-C Single-Bond Cleavage: Achievements and Prospects

This review article emphasizes the C-C bond cleavage in organic synthesis via metal-free approach. Conventional organic synthesis mainly deals with the reactive π bonds and polar σ bonds. In contrast, the ubiquitous C-C single bonds are inherently stable and are less reactive, which poses a challenge to synthetic chemists. Although inert, such C-C single-bond cleavage reactions have gained attention amongst synthetic chemists, as they provide unique and more straightforward routes, with significantly fewer steps. Several review articles have been reported regarding the activation and cleavage of C-C bonds using different transition metals. However, given the high cost and toxicity of many of these metals, the development of strategies under metal-free conditions is of utmost importance. Though many research articles have been published in this area, no review article has been reported so far. Herein, we discuss the reactions in a more concise way from the year 2012 to today, with emphasis on important reactions. Mechanisms of all the reactions are also well addressed. We believe that this review will be beneficial for the readers who work in this field.

Synthesis of (2-(Quinolin-2-yl)phenyl)carbamates by a One-Pot Friedel-Crafts Reaction/Oxidative Umpolung Aza-Grob Fragmentation Sequence

Utilizing the easily available isatin-based propargyl amines prepared from isatins, terminal alkynes, and anilines, (2-(quinolin-2-yl)phenyl)carbamates were prepared by a one-pot reaction in sequence, combining the gold-catalyzed Friedel-Crafts cyclization, oxidative umpolung aza-Grob fragmentation, and nucleophilic addition. In this process, gold-catalyzed cyclization of isatin-based propargyl amines gave 1'H-spiro[indoline-3,2'-quinolin]-2-ones, which were oxidized in situ by hypervalent iodine via the aza-Grob fragmentation to afford isocyano intermediates 2-(2-isocyanatophenyl)quinolines. Followed by the nucleophilic addition with alcohol solvents, (2-(quinolin-2-yl)phenyl)carbamates were synthesized. This procedure features easy operation, a wide substrate scope, and mild conditions.

The Role of Through-Bond Stereoelectronic Effects in the Reactivity of 3-Azabicyclo[3.3.1]nonanes

Hyperconjugation/conjugation through-bond stereoelectronic effects were studied with density functional theory in the context of 3-azabicyclo[3.3.1]nonanes to unravel puzzling differences in reactivity between a vinylogous chloride (4) and a vinylogous ester (5). These compounds─whose structures differ only by one substituent─were found to display strikingly different reactivities in hydrochloric acid by Risch and co-workers ( J. Am. Chem. Soc., 1991, 113, 9411-9412). Computational analyses of substituent effects, noncovalent interactions, natural bond orbitals, isodesmic reactions, and hydration propensities lead to a model for which the role of remote, through-bond stereoelectronic effects is the key to explaining 4 and 5's diverging reactivity.

Hypervalent-iodine promoted selective cleavage of C(sp3)–C(sp3) bonds in ethers

A visible-light-promoted and radical-mediated strategy for the site-specific cleavage of C(sp3)–C(sp3) bonds in ethers is reported.

Rhodium(iii)-catalyzed successive C(sp2)–H and C(sp2)–C(sp2) bond activation of aryl oximes: synthetic and mechanistic studies

A rhodium(iii)-catalyzed redox-neutral reaction of aryl oximes and internal alkynes to generate novel N-(2-cyanoaryl) indanone imines.

Synthesis of a Bicyclo[2.2.1]heptane Skeleton with Two Oxy-Functionalized Bridgehead Carbons via the Diels-Alder Reaction

We describe a synthetic method for a bicyclo[2.2.1]heptane skeleton with two oxy-functionalized bridgehead carbons. This method involves an intermolecular Diels-Alder reaction using 5,5-disubstituted 1,4-bis(silyloxy)-1,3-cyclopentadienes, the diene structure of which has never been synthesized. Furthermore, the intramolecular Diels-Alder reaction using a diene bearing a dienophile moiety at the C-5 position can provide a tricyclic carbon framework that includes the bicyclo[2.2.1]heptane skeleton. The novel bicyclo[2.2.1]heptane derivatives could be utilized as versatile building blocks for organic synthetic chemistry.

Iron-Catalyzed C-C Single-Bond Cleavage of Alcohols

An iron-catalyzed deconstruction/hydrogenation reaction of alcohols through C-C bond cleavage is developed through photocatalysis, to produce ketones or aldehydes as the products. Tertiary, secondary, and primary alcohols bearing a wide range of substituents are suitable substrates. Complex natural alcohols can also perform the transformation selectively. A investigation of the mechanism reveals a procedure that involves chlorine radical improved O-H homolysis, with the assistance of 2,4,6-collidine.

Access to Indole-Annulated Medium-Sized Lactams through Protonation/Deuteration-Induced Ring-Opening of Spiroindolines

A protocol has been developed to access indole-annulated eight- and nine-membered lactams through protonation-induced ring-opening of spiroindolines, which are dearomative Heck products of tetrahydro-β-carbolines or hexahydroazepino[3,4-b]indoles. Brønsted acids and nucleophiles were explored and compared in the transformation. A combination of deuterated hydrochloride and deuterated methanol enables deuterative ring-opening of spiroindolines to afford medium-sized lactam diastereoisomers with a deuterium content ratio around 1:1.

Kinetic Resolution of Spiroindolines through Ir-Catalyzed Asymmetric Allylative Ring-Opening Reaction

Kinetic resolution of racemic spiroindolines with s factors of ≤15200 has been developed to access enantiomerically enriched indole-annulated medium-sized lactams and spiroindolines through Ir-catalyzed asymmetric allylative ring-opening reaction. Density functional theory calculations support the idea that the accurate discrimination of two spiroindoline enantiomers by (η³-allyl)-iridium(III) species and the perfect central-to-axial chirality conversion during C-C bond fragmentation ensure the stereoselective formation of two contiguous stereogenic centers and one axis in the medium-sized lactams.

Selective C-C Bond Cleavage of Cycloalkanones by NaNO2/HCl

A novel selective fragmentation of cycloalkanones by NaNO₂/HCl has been established. The C-C bond cleavage reaction proceeds smoothly under mild conditions, selectively affording versatile keto acids or oxime acids. The methodology can streamline the synthesis of valuable chiral molecules and isocoumarins from readily available feedstocks.

A Synthetic Route to The Core Structure of (-)-Retigeranic Acid A

Retigeranic acid A is a uniquely structured pentacyclic sesterterpene bearing eight stereogenic centers. We report a concise route to the core structure of (-)-retigeranic acid A. The stereochemistry of its six chiral centers and three quaternary carbon centers was well-controlled. This route features two intramolecular Pauson-Khand reactions (IMPKRs): the first forged the D and E rings to deliver the triquinane subunit, and the second constructed the A and B rings and diastereoselectively installed the quaternary C_6a center.

Site-Specific Oxidation of (sp3)C-C(sp3)/H Bonds by NaNO2/HCl

A site-specific oxidation of (sp³)C-C(sp³) and (sp³)C-H bonds in aryl alkanes by the use of NaNO₂/HCl was explored. The method is chemical-oxidant-free, transition-metal-free, uses water as the solvent, and proceeds under mild conditions, making it valuable and attractive to synthetic organic chemistry.

Diastereoselective Access to Tetracyclic Eight-Membered Lactams through a Dearomative Heck Reaction and an Alkylative Ring-Opening Driven by Photoexcited Spiroindolines

An external-photocatalyst-free, light-driven alkylative ring-opening of stable spiroindolines was developed to construct indolo- and benzoannulated eight-membered lactams. The spiroindolines were prepared from tetrahydro-β-carbolines by a dearomative Heck reaction. Mechanistic experimental studies on the alkylative ring opening suggested that a photoredox pathway was involved, in which the spiroindoline performed as both reagent and photosensitizer. DFT calculations showed that the radical addition toward a cyclic alkene was the key to the diastereoselective formation of tetracyclic medium-sized lactams.

Deacylative Carbon-Carbon Bond Cleavage of Ketone Equivalents: Applications to Radical Carbon-Carbon Bond Formation Reactions

This article describes the synthetic application of ketone-derived oxaziridines as alkyl radical precursors in copper-catalyzed Carbon-Carbon bond formation reactions. Experimental and computational studies indicate a free radical mechanism, where alkyl radicals are efficiently generated via cleavage of a Carbon-Carbon bond of oxaziridines. Acyclic and unstrained cyclic oxaziridines are applicable to the present radical process, allowing for the generation of various alkyl radicals with good functional group compatibility.

seco-Labdanes: A Study of Terpenoid Structural Diversity Resulting from Biosynthetic C-C Bond Cleavage

The cleavage of a C-C bond is a complexity generating process, which complements oxidation and cyclisation events in the biosynthesis of terpenoids. This process leads to increased structural diversity in a cluster of related secondary metabolites by modification of the parent carbocyclic core. In this review, we highlight the diversifying effect of C-C bond cleavage by examining the literature related to seco-labdanes-a class of diterpenoids arising from such C-C bond cleavage events.

Spirocyclic Nitroxides as Versatile Tools in Modern Natural Sciences: From Synthesis to Applications. Part I. Old and New Synthetic Approaches to Spirocyclic Nitroxyl Radicals

Spirocyclic nitroxyl radicals (SNRs) are stable paramagnetics bearing spiro-junction at a-, b-, or g-carbon atom of the nitroxide fragment, which is part of the heterocyclic system. Despite the fact that the first representatives of SNRs were obtained about 50 years ago, the methodology of their synthesis and their usage in chemistry and biochemical applications have begun to develop rapidly only in the last two decades. Due to the presence of spiro-function in the SNRs molecules, the latter have increased stability to various reducing agents (including biogenic ones), while the structures of the biradicals (SNBRs) comprises a rigid spiro-fused core that fixes mutual position and orientation of nitroxide moieties that favors their use in dynamic nuclear polarization (DNP) experiments. This first review on SNRs will give a glance at various strategies for the synthesis of spiro-substituted, mono-, and bis-nitroxides on the base of six-membered (piperidine, 1,2,3,4-tetrahydroquinoline, 9,9'(10H,10H')-spirobiacridine, piperazine, and morpholine) or five-membered (2,5-dihydro-1H-pyrrole, pyrrolidine, 2,5-dihydro-1H-imidazole, 4,5-dihydro-1H-imidazole, imidazolidine, and oxazolidine) heterocyclic cores.

Photocatalytic Aerobic Oxidative Ring Expansion of Cyclic Ketones to Macrolactones by Cerium and Cyanoanthracene Catalysis

We describe a cerium-catalyzed aerobic oxidative ring expansion for the expedient construction of synthetically challenging macrolactones under visible-light conditions. Cyanoanthracene has been employed as co-catalyst to accelerate the turnover of the cerium cycle leading to a fast conversion within 20 min of irradiation. Taking advantage of the high efficiency and operationally simple conditions, a collection of over 100 macrolactones equipped with ring systems ranging from 9- to 19-membered macrocycles have been prepared from simple building blocks. Moreover, the enabling potential of this strategy to simplify the generation of molecular complexity has been demonstrated through the concise synthesis of sonnerlactone.

Chlorocyclization/cycloreversion of allylic alcohols to vinyl chlorides

Unprecedented chlorination of allylic alcohols: a simple mix-and-go procedure for the cyclization/cycloreversion of secondary and tertiary allylic alcohols with chloronium ions under mild conditions and practical access to remote carbonyl vinyl chlorides.

Visible-Light Photoredox-Catalyzed Ring-Opening Carboxylation of Cyclic Oxime Esters with CO2

The carboxylation of cyclic oxime esters with carbon dioxide via visible-light photoredox catalysis is demonstrated for the first time. A variety of cyclic oxime esters undergo ring-opening C-C bond cleavage and carboxylation to give cyanoalkyl-containing carboxylic acids in moderate to good yields. Moreover, this methodology features mild reaction conditions (room temperature, 1 atm), wide substrate scope, good functional group tolerance as well as facile derivations of products. Mechanistic studies indicate that the benzylic radicals and anions might be the key intermediates.

Transition Metal-Mediated C-C Single Bond Cleavage: Making the Cut in Total Synthesis

Transition-metal-mediated cleavage of C-C single bonds can enable entirely new retrosynthetic disconnections in the total synthesis of natural products. Given that C-C bond cleavage inherently alters the carbon framework of a compound, and that, under transition-metal catalysis, the generated organometallic or radical intermediate is primed for further complexity-building reactivity, C-C bond-cleavage events have the potential to drastically and rapidly remodel skeletal frameworks. The recent acceleration of the use of transition-metal-mediated cleavage of C-C single bonds in total synthesis can be ascribed to a communal recognition of this fact. In this Review, we highlight ten selected total syntheses from 2014 to 2019 that illustrate how transition-metal-mediated cleavage of C-C single bonds at either the core or the periphery of synthetic intermediates can streamline synthetic efforts.

Rhodium(II)-catalyzed multicomponent assembly of α,α,α-trisubstituted esters via formal insertion of O-C(sp3)-C(sp2) into C-C bonds

The direct cleavage of C(CO)−C single bonds, delivering otherwise inaccessible compounds, is a significant challenge. Although the transition metal-catalyzed insertion of functional groups into C(CO)−C bonds has been studied, strained ketone substrates or chelating assistance were commonly required. In this article, we describe a rhodium(II)-catalyzed three-component reaction of 1,3-diones, diazoesters, and N,N-dimethylformamide (DMF), leading to an unusual formal insertion of O–C(sp³)–C(sp²) into unstrained C(CO)−C bonds. This procedure provides a rapid entry to a gamut of otherwise inaccessible α,α,α-trisubstituted esters/amide from relatively simple substrates in a straightforward manner. 55 examples of highly decorated products demonstrate the broad functional group tolerance and substrate scope. The combination of control experiments and isotope-labeling reactions support that O, C(sp³), and C(sp²) units derive from 1,3-diones, diazoesters, and DMF, respectively.

The direct cleavage of C(CO)−C single bonds is usually restricted to strained ketone substrates or to chelating assistance. Here, the authors show a rhodium(II)-catalyzed three-component reaction of 1,3-diones, diazoesters, and DMF, leading to an unusual formal insertion of O–C(sp³)–C(sp²) into unstrained C(CO)–C bonds.

Asymmetric Total Syntheses of Di- and Sesquiterpenoids by Catalytic C-C Activation of Cyclopentanones

To show the synthetic utility of the catalytic C-C activation of less strained substrates, described here are the collective and concise syntheses of the natural products (-)-microthecaline A, (-)-leubehanol, (+)-pseudopteroxazole, (+)-seco-pseudopteroxazole, pseudopterosin A-F and G-J aglycones, and (+)-heritonin. The key step in these syntheses involve a Rh-catalyzed C-C/C-H activation cascade of 3-arylcyclopentanones, which provides a rapid and enantioselective route to access the polysubstituted tetrahydronaphthalene cores presented in these natural products. Other important features include 1) the direct C-H amination of the tetralone substrate in the synthesis of (-)-microthecaline A, 2) the use of phosphoric acid to enhance efficiency and regioselectivity for problematic cyclopentanone substrates in the C-C activation reactions, and 3) the direct conversion of serrulatane into amphilectane diterpenes by an allylic cyclodehydrogenation coupling.

Recent Advances in the Total Synthesis of Natural Products Containing Eight-Membered Carbocycles (2009-2019)

Natural products containing eight-membered carbocycles constitute a class of structurally intriguing and biologically important molecules such as the famous diterpenes taxol and vinigrol. Such natural products are being increasingly investigated because of their fascinating architectural features and potent medicinal properties. However, synthesis of natural products with cyclooctane moieties has proved to be highly challenging. This review highlights the recently completed total syntheses of natural products with eight-membered carbocycles with a focus on strategic considerations. A collection of 27 representative studies from the literature covering the decade from 2009 to 2019 is described in chronological order with relevant studies grouped together, including syntheses of the same natural product by different research groups using different strategies. Finally, a summary and outlook including a discussion of the major features of each strategy used in the syntheses are presented. This review illustrates the diversity and creativity in the elegant synthetic designs of eight-membered carbocycles. We hope this review will provide timely illumination and beneficial guidance for future synthetic efforts for organic chemists who are interested in this area.

Tipping the balance: theoretical interrogation of divergent extended heterolytic fragmentations

Herein we interrogate a type of heterolytic fragmentation reaction called a 'divergent fragmentation' using density functional theory (DFT), natural bond orbital (NBO) analysis, ab initio molecular dynamics (AIMD), and external electric field (EEF) calculations. We demonstrate that substituents, electrostatic environment and non-statistical dynamic effects all influence product selectivity in reactions that involve divergent fragmentation pathways. Direct dynamics simulations reveal an unexpected post-transition state bifurcation (PTSB), and EEF calculations suggest that some transition states for divergent pathways can, in principle, be selectively stabilized if an electric field of the correct magnitude is oriented appropriately.

Ruthenium(ii)-catalyzed chemoselective deacylative annulation of 1,3-diones with sulfoxonium ylides via C-C bond activation

The first successful example of deacylative annulation of 1,3-diones with sulfoxonium ylides was achieved through Ru(ii)-catalyzed C-C bond activation. The excellent chemoselectivity and broad substrate scope render this method a practical and versatile approach for the preparation of (hetero)aryl and alkenyl substituted furans, which are valuable units in many biologically active compounds and functional materials. A preliminary mechanistic study reveals that this process involves a deacylative α-ruthenation to generate key alkyl Ru(ii) intermediates with the release of a benzoic acid fragment.

Acid-Catalyzed Air-Oxidative Fragmentation of the Carbon-Carbon Bond in 2-Aryl-1-tetralones

Catalytic auto-oxidation with air is a highly desirable method for green synthesis. Described here is a method for acid-catalyzed one step air-oxidative fragmentation of 2-aryl-1-tetralones to alkyl-2-(3-oxo-3-aryl) benzoates in the presence of alcohol. This method was then demonstrated using concise synthesis of a key intermediate of antiasthma drug Montelukast sodium. Moreover, the paradoxical nature of the reaction in which ester forms but only within a low concentration threshold of alcohol helps in understanding the mechanism of the reaction.