Cyclopropane Derivatives and their Diverse Biological Activities

Dynamic stereomutation of vinylcyclopropanes with metalloradicals

The ever increasing demands for greater sustainability and lower energy usage in chemical processes call for fundamentally new approaches and reactivity principles. In this context, the pronounced prevalence of odd-oxidation states in less precious metals bears untapped potential for fundamentally distinct reactivity modes via metalloradical catalysis1-3. Contrary to the well-established reactivity paradigm that organic free radicals, upon addition to a vinylcyclopropane, lead to rapid ring opening under strain release-a transformation that serves widely as a mechanistic probe (radical clock)4 for the intermediacy of radicals5-we herein show that a metal-based radical, that is, a Ni(I) metalloradical, triggers reversible cis/trans isomerization instead of opening. The isomerization proceeds under chiral inversion and, depending on the substitution pattern, occurs at room temperature in less than 5 min, requiring solely the addition of the non-precious catalyst. Our combined computational and experimental mechanistic studies support metalloradical catalysis as origin of this profound reactivity, rationalize the observed stereoinversion and reveal key reactivity features of the process, including its reversibility. These insights enabled the iterative thermodynamic enrichment of enantiopure cis/trans mixtures towards a single diastereomer through multiple Ni(I) catalysis rounds and also extensions to divinylcyclopropanes, which constitute strategic motifs in natural product- and total syntheses6. While the trans-isomer usually requires heating at approximately 200 °C to trigger thermal isomerization under racemization to cis-divinylcyclopropane, which then undergoes facile Cope-type rearrangement, the analogous contra-thermodynamic process is herein shown to proceed under Ni(I) metalloradical catalysis under mild conditions without any loss of stereochemical integrity, enabling a mild and stereochemically pure access to seven-membered rings, fused ring systems and spirocycles.

In vitro cytotoxic activity on KATO-III cancer cell lines of mangiferolic acid purified from Thai Tetragonula laeviceps propolis

Gastric cancer is a global health concern, but current treatment with chemotherapy and surgery is often inadequate, prompting the exploration of alternative treatments. Propolis is a natural substance collected by bees known for its diverse properties linked to floral sources. The Dichloromethane Partitioned Extract (DPE) from Tetragonula laeviceps propolis, in Bankha district, Thailand was previously shown to possess significant cytotoxicity against KATO-III gastric cancer cells, while showing lower cytotoxicity toward WI-38 normal fibroblast cells. Here, the DPE was further fractionated by column chromatography, identified active fractions, and subjected to structural analysis using nuclear magnetic resonance spectroscopy. Cytotoxicity against KATO-III cells was reevaluated, and programmed cell death was analyzed using flow cytometry. Expression levels of cancer-related genes were measured using quantitative real-time reverse transcriptase PCR. Cardol C15:2 (compound 1) and mangiferolic acid (MF; compound 2) were discovered in the most active fractions following structural analysis. MF exhibited strong cytotoxicity against KATO-III cells (IC50 of 4.78-16.02 μg/mL), although this was less effective than doxorubicin (IC50 of 0.56-1.55 μg/mL). Morphological changes, including decreased cell density and increased debris, were observed in KATO-III cells treated with 30 μg/mL of MF. Significant induction of late-stage apoptosis and necrosis, particularly at 48 and 72 h, suggested potential DNA damage and cell cycle arrest, evidenced by an increased proportion of sub-G1 and S-phase cells. Doxorubicin, the positive control, triggered late apoptosis but caused more necrosis after 72 h. Furthermore, MF at 30 μg/mL significantly increased the expression level of COX2 and NFκB genes linked to inflammation and cell death pathways. This upregulation was consistent at later time points (48 and 72 h) and was accompanied by increased expression of CASP3 and CASP7 genes. These findings suggest MF effectively induces cell death in KATO-III cells through late apoptosis and necrosis, potentially mediated by upregulated inflammation-related genes.

Enantioselective α-Boryl Carbene Transformations

Carbenes, recognized as potent intermediates, enable unique chemical transformations, and organoborons are pivotal in diverse chemical applications. As a hybrid of carbene and the boryl group, α-boryl carbenes are promising intermediates for the construction of organoborons; unfortunately, such carbenes are hard to access and have low structural diversity with their asymmetric transformations largely uncharted. In this research, we utilized boryl cyclopropenes as precursors for the swift synthesis of α-boryl metal carbenes, a powerful category of intermediates for chiral organoboron synthesis. These α-boryl carbenes undergo a series of highly enantioselective transfer reactions, including B-H and Si-H insertion, cyclopropanation, and cyclopropanation/Cope rearrangement, catalyzed by a singular chiral copper complex. This approach opens paths to previously unattainable but easily transformable chiral organoborons, expanding both carbene and organoboron chemistry.

Alkene carboamination/oxidative denitrogenation of 3-allyl-3-hydrazinylindolin-2-ones: one-pot entry to spirocyclopropyloxindoles

A one-pot protocol, consisting of a Pd-catalysed carboamination reaction, followed by N-deprotection and oxidative denitrogenation, has been developed for the synthesis of diversely substituted spirocyclopropyloxindoles, in yields up to 73% and with diastereoselectivity close to 1 : 1. Readily accessible starting materials, mild reaction conditions, an easy to operate one-pot procedure and good functional group tolerance make this transformation a versatile tool for the synthesis of substituted spirocyclopropyloxindoles. This protocol successfully works on the gram-scale and allows access to both diastereoisomers separately. A plausible mechanism was proposed, and a series of post-transformations were performed on the obtained products, showing their remarkable synthetic versatility.

Amberlyst-A26-Mediated Corey-Chaykovsky Cyclopropanation of 9-Alkylidene-9H-fluorene under Continuous Process

Herein, we have developed a continuous-process for the direct cyclopropanation of various alkenes nonconjugated with carbonyl using trimethylsulfoxonium iodide as a methylene source via the Corey-Chaykovsky cyclopropanation reaction in the presence of Amberlyst-A26 as a heterogeneous base. Several 9-alkylidene-9H-fluorene derivatives successfully undergo Corey-Chaykovsky cyclopropanation to afford spiro[cyclopropane-1,9'-fluorene] in excellent yields under the continuous-process module. Furthermore, continuous process for the cyclopropanation of 3-benzylideneindolin-2-one derivatives using Amberlyst-A26 as a heterogeneous base has been described, which afford spiro[cyclopropane-1,3'-indolin]-2'-one derivatives.

Photocatalyzed Borylcyclopropanation of Alkenes with a (Diborylmethyl)iodide Reagent

Cyclopropane skeletons play a prominent role in the development of organic synthesis and pharmaceutical chemistry. Herein, we report the design and synthesis of a stable, multifunctional (diborylmethyl)iodide reagent (CHI(Bpin)2 ) for the photoinduced cyclopropanation of alkenes, providing an array of 1,2-substituted cyclopropylboronates in good yields. This α-haloboronic ester can be readily synthesized on a multigram scale from commercially available starting materials. Furthermore, the protocol displays high chemo- and diastereoselectivity, excellent functional-group tolerance, and allows for late-stage borylcyclopropanation of complex molecules. Mechanistic studies reveal that the borylcyclopropanation proceeds through a radical addition/polar cyclization pathway mediated by the photocatalyst fac-Ir(ppy)3 and visible light.

Photosensitized O2 enables intermolecular alkene cyclopropanation by active methylene compounds

Cyclopropanes are key features in many preclinical, clinical, and commercial drugs, as well as natural products. The most prolific technique for their synthesis is the metal-catalyzed reaction of an alkene with a diazoalkane, a highly energetic reagent requiring stringent safety precautions. Discovery of alternative innocuous reagents remains an ongoing challenge. Herein, we report a simple photoredox-catalyzed intermolecular cyclopropanation of unactivated alkenes with active methylene compounds. The reaction proceeds in neutral solvent under air or dioxygen (O2) with a photoredox catalyst excited by blue light-emitting diode light and an iodine co-catalyst that is either added as molecular iodine or generated in situ from alkyl iodides. Mechanistic investigations indicate that photosensitized O2 plays a vital role in the generation of carbon-centered radicals for both the addition of active methylene compounds to alkenes and the ring closure.

Base-promoted cyclization of ortho-hydroxyacetophenones with in situ generated cyclopropenes: diastereoselective access to spirobenzo[b]oxepines and related precursors

An unprecedented [5 + 2] spirocyclization route to obtain a vital class of functionalized spirobenzo[b]oxepine-cyclopropanes in good to high yields with excellent diastereoselectivities is reported. This domino reaction proceeds through a regioselective oxa-Michael addition of ortho-hydroxyacetophenones as 1,5-binucleophiles to in situ produced highly reactive cyclopropenes from 2-aroyl-1-chlorocyclopropanecarboxylates triggered by Cs₂CO₃ and the subsequent intramolecular aldol reaction under heating conditions, enabling the formation of new C-O and C-C bonds for benzo[b]oxepine ring synthesis. Moreover, at ambient temperature, the above C-O/C-C bond-forming event takes place preferentially via a [4 + 2] annulation path over a spirocyclization route, leading to substituted fused-cyclopropanes with good diastereoselectivities. Gratifyingly, further alterations of the obtained spirobenzo[b]oxepines and tetrahydrocyclopropa[b]chromenes afford fascinating classes of 4H-chromen-4-ones and cyclopenta[c]chromenes, respectively, under metal-free conditions.

Asymmetric C(sp3)-H borylation: an update

Chiral organoboronates have emerged as a key intermediate in the development of pharmaceuticals and materials science. Therefore, several attempts have been made to design various synthetic methods to easily furnish these compounds during the past few decades. Inter alia, asymmetric catalysis has been increasing rapidly as a viable, practical and beneficial strategy for their preparation. In this respect, recent years have witnessed significant progress in aliphatic C-H borylation as the generated carbon-boron bonds are largely utilized to produce other carbon-carbon, carbon-nitrogen and carbon-oxygen bonds. This review presents a detailed overview and analysis of transition metal-catalyzed asymmetric C(sp³)-H borylation strategies. Overall, it assembles all the recent developments in this particular synthetic avenue up to March 2022.

Asymmetric Synthesis of Tertiary and Secondary Cyclopropyl Boronates via Cyclopropanation of Enantioenriched Alkenyl Boronic Esters

The cyclopropanation of alkenyl boronates and subsequent derivatization of the boronate handle are a convenient strategy to quickly build molecular complexity and access diverse compounds with a high sp³ fraction. Herein, we describe the asymmetric cyclopropanation of enantioenriched hydrobenzoin-derived alkenyl boronic esters toward the synthesis of tertiary and secondary cyclopropyl boronates.

Synthesis of New Spiro-Cyclopropanes Prepared by Non-Stabilized Diazoalkane Exhibiting an Extremely High Insecticidal Activity

The synthesis of new insecticidal gem-dimethyspiro-cyclopropanes derived from pyrrolidine-2,3-dione have been described, and their biological effect against different insect species has been evaluated. The presented results demonstrate the excellent insecticidal activity of cyclopropane 5c against Aedes aegypti and Musca domestica. Cyclopropane 5c showed the quickest knockdown and the best killing against Aedes aegypti and Musca domestica compared to trans-chrysanthemic acid and pyrethrin. The biological results of the high insecticidal activity were confirmed by the results of docking. This is evident in the binding affinity obtained for cyclopropane 5c, indicating good binding with an important active amino acid residue of the 5FT3 protein.

Reductive Ring Opening of Arylcyclopropanecarboxamides Accompanied by Borylation and Enolate Formation

Treatment of arylcyclopropanecarboxamides with a sodium dispersion in the presence of methoxypinacolborane as a reduction-resistant electrophile leads to reductive cleavage of the cyclopropane ring followed by instant trapping with the boron electrophile to yield the enolates of γ-aryl-γ-borylalkanamides. The enolates react further with a different electrophile to yield the corresponding α-substituted amides with anti selectivity.

Discovery of a Cryptic Nitro Intermediate in the Biosynthesis of the 3-(trans-2'-Aminocyclopropyl)alanine Moiety of Belactosin A

Belactosin A, a β-lactone proteasome inhibitor, contains a unique 3-(trans-2'-aminocyclopropyl)alanine moiety. We recently identified the biosynthetic gene cluster of the belactosin series from Streptomyces sp. UCK14. To shed light on the formation of the aminocyclopropylalanine, we established a heterologous pathway expression, constructed a set of gene deletion mutants, and performed feeding studies for a chemical complementation that include the incorporation of stable isotope-labeled precursors. We thereby show that, in the biosynthesis of this building block, a cryptic nitrocyclopropylalanine intermediate is generated from l-lysine. The subsequent reduction of the N-oxygenated precursor to the corresponding amine is mediated by the molybdopterin-dependent enzyme BelN.

Insights into gold-catalyzed formation of aza-heterocycles using benzofuroxans as nitrene transfer reagents: mechanism and origins of chemoselectivity

Density functional theory (DFT) calculations have been performed to reveal the mechanism of gold(i)-catalyzed annulation of N-allylynamides and benzofuroxans as nitrene transfer reagents to construct azaheterocyclic compounds. The calculated results revealed that the reaction mechanism mainly undergoes eight processes. Among the reaction steps, intramolecular nucleophilic attack of the imino N atom on the α-position of activated gold keteniminium is a rate-determining process, which is different from that proposed previously by experiment. The chemoselectivity of the products is controlled by competition between the cyclopropanation of α-imino gold carbenes and intramolecular nucleophilic attack of the phenyl ring on α-imino gold carbenes, and could be explained by NPA charge. The different yields of cyclopropanated product in different solvents are dictated by the relative polarity leading to the different energy barriers of the rate-determining steps. The present work expounds the experimental observation at the molecular level and is informative for exploring efficient syntheses of 3-azabicyclo[3.1.0]hexanes.

DFT calculations were employed to study the mechanism and origin of chemoselectivity of gold-catalyzed annulation of N-allylynamides and benzofuroxans as nitrene transfer reagents.

Intramolecular Photochemical [2+1]-Cycloadditions of Nucleophilic Siloxy Carbenes

Visible light induced singlet nucleophilic carbenes undergo rapid [2 + 1]-cycloaddition with tethered olefins to afford unique bicyclo[3.1.0]hexane and bicyclo[4.1.0]heptane scaffolds. This cyclopropanation process requires only visible light irradiation to proceed, circumventing the use of exogenous (photo)catalysts, sensitisers or additives and showcases a vastly underexplored mode of reactivity for nucleophilic carbenes in chemical synthesis. The discovery of additional transformations including a cyclopropanation/retro-Michael/Michael cascade process to afford chromanones and a photochemical C–H insertion reaction are also described.

Visible light induced singlet nucleophilic carbenes undergo rapid [2 + 1]-cycloaddition with tethered olefins to afford unique bicyclo[3.1.0]hexane and bicyclo[4.1.0]heptane scaffolds.

Engineering Pyrrolysyl-tRNA Synthetase for the Incorporation of Non-Canonical Amino Acids with Smaller Side Chains

Site-specific incorporation of non-canonical amino acids (ncAAs) into proteins has emerged as a universal tool for systems bioengineering at the interface of chemistry, biology, and technology. The diversification of the repertoire of the genetic code has been achieved for amino acids with long and/or bulky side chains equipped with various bioorthogonal tags and useful spectral probes. Although ncAAs with relatively small side chains and similar properties are of great interest to biophysics, cell biology, and biomaterial science, they can rarely be incorporated into proteins. To address this gap, we report the engineering of PylRS variants capable of incorporating an entire library of aliphatic "small-tag" ncAAs. In particular, we performed mutational studies of a specific PylRS, designed to incorporate the shortest non-bulky ncAA (S-allyl-l-cysteine) possible to date and based on this knowledge incorporated aliphatic ncAA derivatives. In this way, we have not only increased the number of translationally active "small-tag" ncAAs, but also determined key residues responsible for maintaining orthogonality, while engineering the PylRS for these interesting substrates. Based on the known plasticity of PylRS toward different substrates, our approach further expands the reassignment capacities of this enzyme toward aliphatic amino acids with smaller side chains endowed with valuable functionalities.

Enantioselective Catalytic Cyclopropanation-Rearrangement Approach to Chiral Spiroketals

A highly enantioselective synthesis of chiral heterobicyclic spiroketals is reported via a "one-pot" cyclopropanation-rearrangement (CP-RA) cascade reaction that is sequentially catalyzed by a chiral Rh(II) catalyst and tetrabutylammonium fluoride (TBAF). Exocyclic vinyl substrates form spirocyclopropanes with tert-butyldimethylsilyl-protected enoldiazoacetates in excellent yields and with excellent enantioselectivities when catalyzed by chiral dirhodium(II) carboxylates, and following desilylation with simultaneous rearrangement in the presence of TBAF, they give (S)-spiroketals in high yields with excellent chirality retention (>95% ee).

Synthesis of β-Lactams and β-Homoprolines by Fragmentative Rearrangement of 5-Spirocyclopropaneisoxazolidines Mediated by Acids

Azetidinones and β-amino acids serve as useful building blocks in synthetic organic chemistry and their structural motifs are often found in biologically active compounds. Due to the importance of these compounds, several synthetic strategies have been developed and availability of new synthetic approaches is highly desirable. In this account, we describe the development of an original method that allows the preparation of β-lactam and β-homoproline derivatives not easily accessible through traditional processes. The serendipitous discovery made in our lab in 2000 involved the formation of a β-lactam by heating a mixture of an alkylidenecyclopropane tethered to a formyl group with N-methylhydroxylamine hydrochloride. Investigation of the process resulted in disclosing an alternative synthetic method of azetidinones based on an acid induced fragmentative rearrangement of cycloadducts of nitrones with suitable methylenecyclopropane derivatives. Herein, the scope of this process is reviewed. In addition, both experimental and computational studies of the mechanism for this peculiar fragmentative rearrangement are presented.

Antibacterial Activity of Synthesized Derivatives of Purpurin Containing Cyсlopropane and Cyclobutane Fragment

The present study is a continuation of the scientific research works for the synthesis of anthraquinonе-containing derivatives with cyclic ring systems by the interaction of 1,2,4-trihydroxyanthraquinone (purpurin) with cyclopropanecarboxylic acid chloride and cyclobutanecarboxylic acid chloride by using the ultrasonic treatment. Esters of purpurin, studied for antibacterial activity in museum test strains of microorganisms (Staphylococcus aureus ATCC 6538-P, Bacillus subtilis ATCC 6633, Escherichia coli ATCC 25922, Pseudomonas aeruginosa АТСС 27853, Сandida albicans АТСС 10231) in vitro with the determination of the minimum inhibitory concentration (MIC) value. The study revealed that the cyclopropane substituent exhibits moderate antibacterial activity against Bacillus subtilis ATCC 6633. While with the cyclobutane moiety it had a weak effect with respect to Pseudomonas aeruginosa ATCC strain. It has been found that the compounds with the cyclopropane and cyclobutane fragment have possessed antimicrobial activity in relation to strains of microorganisms Staphylococcus aureus АТСС 6538 for which the MIC value was 62.5 μg/ml.

Ring-Opening/Recyclization Cascades of Monoactivated Cyclopropanes

A variety of cyclopropyl aryl ketones undergo uncatalyzed cascade ring-opening/recyclization reactions to generate indenones and fluorenones. In addition, a new strategy to access 3-hydroxyindanones possessing two contiguous stereogenic centers, one of them being an all-carbon quaternary center, was also established. During the course of the investigation, pronounced solvent, temperature, and substituent effects on the product distribution were discovered.

A highly efficient method for the construction of cyclopropane-containing dihydroindole derivatives from indolemethylenecyclopropanes with DIAD and DEAD

A highly efficient method for the construction of cyclopropane-containing dihydroindole derivatives from indolemethylenecyclopropanes with DIAD and DEAD has been disclosed. The transformation could occur under catalyst-free conditions at ambient temperature to afford dihyroindole derivatives in good yields. It has been proved that the strained moiety of methylenecyclopropane in the substrate of indolemethylenecyclopropane is critical and DFT calculations reveal that the reaction proceeds through a two-step pathway.

Gold(iii)-catalyzed chemoselective annulations of anthranils with N-allylynamides for the synthesis of 3-azabicyclo[3.1.0]hexan-2-imines

We herein report the gold(iii)-catalyzed selective annulation of anthranils with N-allylynamides under mild conditions. By trapping the in situ-generated α-imino gold carbenes, 3-azabicyclo[3.1.0]hexan-2-imines were obtained in high synthetic efficiency. The reaction, which can be conducted in the gram scale, tolerates electron-rich and electron-deficient anthranils as well as a diverse set of functionalized ynamides (aryl- and alkyl-substituted terminal).

The Search for Biologically Active Compounds in the Series of N-ethoxyethylpiperidine Derivatives

With the aim to introduce fragment of cyclopropane and fragments of p-, m-, o-fluorophenyls into the structures of N-ethoxyethylpiperidines, acylation of oxime and phenylacetylenic alcohol of 1-(2-ethoxyethyl)-4-ketopiperidine by cyclopropanecarbonylchloride was carried out; on the basis of 1-(2-ethoxyethyl)-4-ethynyl-4-hydroxypiperidine (cascaine alcohol), acylation by 4-fluoro-, 3-fluoro-, 2-fluorobenzoylchlorides was carried out with formation of the corresponding piperidine containing hydrochlorides of cyclopropanecarboxylic acid esters and para-, meta-, ortho-fluorobenzoic esters. Acylation reaction on the hydroxyl group of compounds is carried out in absolute dioxane, the acylating agents are cyclopropanecarbonylchloride, p-, m-, o-fluorobenzoyl chlorides taken in excess. The obtained esters of cyclopropanecarboxylic and para-, meta-, ortho-fluorobenzoic acids are crystalline substances with a clear melting point, well soluble in water, ethanol, acetone. P-fluorobenzoates are obtained with better yields, m-fluorobenzoates occupy an intermediate position, and o-fluorobenzoates are formed with the lowest yields. The best yields of fluorobenzoates are obtained using dioxane as a solvent. Para-, meta-, ortho-fluorobenzoic esters of 1-(2-ethoxyethyl)-4-ethynyl-4-hydroxypiperidine coded A-4 – A-6 were studied for the presence of antimicrobial activity, the actions of these preparations were evaluated in vitro in relation to strains of gram-positive bacteria Staphylococcus aureus, Bacillus subtilis, gram-negative strains of Escheriсhia coli, Pseudomonas aeruginosa and to yeast fungus Сandida albicans by the diffusion method into agar (holes). Introduction of fluorine atom into the structure of cascaine lead to manifestation of antimicrobial activity.

Chemoselective syntheses of spirodihydrofuryl and spirocyclopropyl barbiturates via cascade reactions of barbiturate-based olefins and acetylacetone

The Michael addition initiated ring closure reaction of barbiturate-based olefins and acetylacetone with NBS has been explored. The efficient and chemoselective approach for the synthesis of barbiturate-fused spirocycles was established. Spirodihydrofuryl barbiturates and spirocyclopropyl barbiturates were synthesized selectively via cascade reactions under different basic conditions in moderate to excellent yields. The structure of 2-(4-chlorophenyl)-1,1-diacetyl-5,7-dimethyl-5,7-diazaspiro[2,5]octane-4,6,8-trione was confirmed by single crystal X-ray diffraction analysis.

Synthesis and Photolysis of Hexahydropyrrolo[3,4-c]pyrazole derivatives

The 1,3-dipolar cycloaddition of 2-diazopropane 1 with N-arylcitraconimides and N-arylmaleimides 2, at −78°C, has led to monoadducts 3. The same addition of 2-diazopropane with maleimide 4, has led to a new and unexpected Δ3-1,3,4-oxadiazoline 5. Irradiation of the pyrazolines 3 led to clean extruction of nitrogen to give the cyclopropanes 6.

Sigmatropic rearrangements of cyclopropenylcarbinol derivatives. Access to diversely substituted alkylidenecyclopropanes

Cyclopropenes constitute useful precursors of other classes of compounds incorporating a three-membered ring. Although the transformation of substituted cyclopropenes into alkylidenecyclopropanes can be accomplished through different strategies, this review is focusing specifically on the use of [2,3]- and [3,3]-sigmatropic rearrangements involving cyclopropenylcarbinol derivatives as substrates. These sigmatropic rearrangements, which have been developed in recent years, allow a remarkably efficient and stereoselective access to a wide variety of heterosubstituted and/or functionalized alkylidenecyclopropanes which would not be readily accessible by other strategies. The different [2,3]- and [3,3]-sigmatropic rearrangements of cyclopropenylcarbinol derivatives disclosed to date, as well as the analysis of their substrate scope and some applications of the products arising from those reactions, are presented in this review.

Regio- and Stereoselective Synthesis of Functionalized Dihydropyridines, Pyridines, and 2H-Pyrans: Heck Coupling of Monocyclopropanated Heterocycles

A palladium-catalyzed coupling between aryl halides and monocyclopropanated pyrroles or furans has been developed, leading to valuable six-membered N- and O-heterocycles. As the key step, a selective cleavage of the non-activated endocyclic C-C bond of the 2-heterobicyclo-[3.1.0]hexane framework is achieved. The developed method offers access to highly functionalized piperidines, pyridines, and pyrans that are challenging to access by traditional methods.

Synthesis of Cyclopropanoids via Substrate-Based Cyclization Pathways

A series of unexpected reactions triggered by the dimethyloxosulfonium methylide led to the discovery of unconventional approaches for the synthesis of cyclopropa-fused tetralones and indeno-spirocyclopropanes. These highly functionalized structures were further elaborated in one step to privileged scaffolds such as tetralones, indenones, and fluorenones. As a whole, the results presented herein establish new diversity-oriented folding pathways.

Rhodium catalysed enantioselective synthesis of mono-(halo)-methyl-cyclopropanes

The catalytic asymmetric synthesis of mono-fluoro-, -chloro- and -bromomethyl-1,2-diaryl ester cyclopropanes is described.

Copper-catalyzed cyclopropanation reaction of but-2-ene

The mechanism of the copper(I)-catalyzed cyclopropanation reaction for methyl diazoacetate with both (Z)- and (E)-but-2-ene stereoisomers has been studied using the 6-311++G(d,p) basis set by means of M06-2X and O3LYP functionals. According to both methods, the rate-limiting step is the formation of a copper-carbene intermediate, formed by association between methyl diazoacetate and bis(acetonitrile)-copper(I) ion with the concomitant extrusion of dinitrogen. Cis/trans diastereoselectivity for the cyclopropanation reaction of a 1,2-disubstituted alkene ((Z)-but-2-ene) has been theoretically studied for the first time through the proper location of transition states on the potential-energy surface with the O3LYP method, since no transition structures could be found with the M06-2X functional due to the extreme flatness of the potential-energy surface. The calculated stereoselectivities involving two acetonitrile ligands or one dichloromethane molecule show qualitative agreement with experimental data. This study allows attributing the origin of the selectivity to steric interactions between the ligands of the catalyst system and the olefin substituents. The comparison between the corresponding activation barriers for the direct insertion step shows a higher reactivity for the Z stereoisomer of but-2-ene, consistently with the larger reactant destabilization through steric interactions.