The "Cyclopropyl Fragment" is a Versatile Player that Frequently Appears in Preclinical/Clinical Drug Molecules

Rapid and Modular Access to Vinyl Cyclopropanes Enabled by Air-stable Palladium(I) Dimer Catalysis

While vinyl cyclopropanes are valuable functional groups in drugs or natural products as well as established precursors to trigger a rich variety of synthetic transformations, their reactive nature can make their installation via direct catalytic approaches challenging. We herein present a modular access to (di)vinyl cyclopropanes under very mild conditions and full conservation of stereochemistry, allowing access to the cis or trans cyclopropane- as well as E or Z vinyl-stereochemical relationships. Our protocol relies on air-stable dinuclear Pd^I catalysis, which enables rapid (<30 min) and selective access to a diverse range of vinyl cyclopropane motifs at room temperature, even on gram scale.

Organocatalyzed Visible Light-Mediated gem-Borosilylcyclopropanation

The borosilylcyclopropanation of styrene derivatives using a (diiodo(trimethylsilyl)methyl)boronic ester carbene precursor is reported herein. The key reagent was synthesized in a 4-step sequence using inexpensive and commercially available starting materials. This method enabled the preparation of novel 1,1,2-tri- and 1,1,2,2-tetrasubstituted borosilylcyclopropanes up to excellent yields and diastereoselectivity. The reaction is organocatalyzed by eosin Y in the presence of visible light. A mechanism consistent with the experimental observations was postulated based on density functional theory calculations. The versatility of these entities was highlighted through post-functionalization reactions.

Alkyne Polymers from Stable Butatriene Homologues: Controlled Radical Polymerization of Vinylidenecyclopropanes

Controlled polymerization of cumulenic monomers represents a promising yet underdeveloped strategy toward well-defined alkyne polymers. Here we report a stereoelectronic effect-inspired approach using simple vinylidenecyclopropanes (VDCPs) as butatriene homologues in controlled radical ring-opening polymerizations. While being thermally stable, VDCPs mimic butatrienes via conjugation of the cyclopropane ring. This leads to exclusive terminal-selective propagation that affords a highly structurally regular alkyne-based backbone, featuring complete ring-opening and no backbiting regardless of polymerization conditions.

Design, Synthesis and Biological Evaluation of Quinazolinamine Derivatives as Breast Cancer Resistance Protein and P-Glycoprotein Inhibitors with Improved Metabolic Stability

A series of twenty-two quinazolinamine derivatives showing potent inhibitory activities on breast cancer resistance protein (BCRP) and p-glycoprotein (P-gp) were synthesized. A cyclopropyl-containing quinazolinamine 22 was identified as a dual BCRP and P-gp inhibitor, while azide-containing quinazolinamine 33 showed BCRP inhibitory activity. These lead compounds were further investigated in a battery of mechanistic experiments. Compound 22 changed the localization of BCRP and P-gp in cells, thus inhibiting the efflux of anticancer drugs by the two ATP-binding cassette (ABC) transporters. In addition, both 22 and 33 significantly stimulated the ATP hydrolysis of the BCRP transporter, indicating that they can be competitive substrates of the BCRP transporter, and thereby increase the accumulation of mitoxantrone in BCRP-overexpressing H460/MX20 cells. Azide derivative 33, exhibited a greater inhibitory effect on BCRP after UV activation and can serve as a valuable probe for investigating the interactions of quinazolinamine derivatives with BCRP. Notably, the dual BCRP and P-gp inhibitors 4-5, 22-24, 27, and BCRP inhibitor 33 showed improved metabolic stability compared to Ko143.

Protoglobin-Catalyzed Formation of cis-Trifluoromethyl-Substituted Cyclopropanes by Carbene Transfer

Trifluoromethyl-substituted cyclopropanes (CF3 -CPAs) constitute an important class of compounds for drug discovery. While several methods have been developed for synthesis of trans-CF3 -CPAs, stereoselective production of corresponding cis-diastereomers remains a formidable challenge. We report a biocatalyst for diastereo- and enantio-selective synthesis of cis-CF3 -CPAs with activity on a variety of alkenes. We found that an engineered protoglobin from Aeropyrnum pernix (ApePgb) can catalyze this unusual reaction at preparative scale with low-to-excellent yield (6-55 %) and enantioselectivity (17-99 % ee), depending on the substrate. Computational studies revealed that the steric environment in the active site of the protoglobin forced iron-carbenoid and substrates to adopt a pro-cis near-attack conformation. This work demonstrates the capability of enzyme catalysts to tackle challenging chemistry problems and provides a powerful means to expand the structural diversity of CF3 -CPAs for drug discovery.

Synthesis of New Azetidine and Oxetane Amino Acid Derivatives through Aza-Michael Addition of NH-Heterocycles with Methyl 2-(Azetidin- or Oxetan-3-Ylidene)Acetates

In this paper, a simple and efficient synthetic route for the preparation of new heterocyclic amino acid derivatives containing azetidine and oxetane rings was described. The starting (N-Boc-azetidin-3-ylidene)acetate was obtained from (N-Boc)azetidin-3-one by the DBU-catalysed Horner-Wadsworth-Emmons reaction, followed by aza-Michael addition with NH-heterocycles to yield the target functionalised 3-substituted 3-(acetoxymethyl)azetidines. Methyl 2-(oxetan-3-ylidene)acetate was obtained in a similar manner, which was further treated with various (N-Boc-cycloaminyl)amines to yield the target 3-substituted 3-(acetoxymethyl)oxetane compounds. The synthesis and diversification of novel heterocyclic amino acid derivatives were achieved through the Suzuki-Miyaura cross-coupling from the corresponding brominated pyrazole-azetidine hybrid with boronic acids. The structures of the novel heterocyclic compounds were confirmed via ¹H-, ¹³C-, ¹⁵N-, and ¹⁹F-NMR spectroscopy, as well as HRMS investigations.

Picolinamide Ligands: Nickel-Catalyzed Reductive Cross-Coupling of Aryl Bromides with Bromocyclopropane and Beyond

The arylcyclopropane motif as the combination of aryl and cyclopropyl ring systems can be found in an increasing amount of approved and investigational drugs. Herein, we have developed a mild, efficient nickel-catalyzed reductive cross-coupling protocol, featuring a simple Ni(II) precatalyst and a novel picolinamide NN₂ pincer ligand. A variety of (hetero)aryl bromides could successfully couple with cyclopropyl bromide to furnish the valued arylcyclopropanes in good to excellent yields. This method is applicable to other alkyl bromides as well. Notably, the reaction is tolerant of a broad range of functionalities including free amines. Furthermore, the synthesis of several significant intermediates of bioactive molecules was achieved in grams, proving the practicability of this method.

Structure-guided design of novel HEPT analogs with enhanced potency and safety: From Isopropyl-HEPTs to Cyclopropyl-HEPTs

Members of the HEPT class are potential non-nucleoside inhibitors of HIV-1 reverse transcriptase. Our previously disclosed one representative HEPT analog 2 produced potent inhibitory activity against wild-type HIV-1 (EC₅₀ = 63.0 nM), but its high cytotoxicity and low selectivity index still needs to be improved (CC₅₀ = 34.0 μM, SI = 565). In this work, a series of novel cyclopropyl-substituted HEPT analogs were developed by substituting a cyclopropyl ring for the isopropyl group at the C-5 position of 2 with the purpose of improving its potency and safety. Of this series, the most potent compound 9h featuring a 2,5-fluoro substitution on the C-6 benzene ring exerted significantly increased inhibitory activity toward wild-type HIV-1 (EC₅₀ = 0.017 μM), which was 4-fold more active than the lead compound 2. The cytotoxicity of 9h was also reduced with much higher selectivity index (SI > 2328). This compound possessed good pharmacokinetics profiles and potential safety: (1) No obvious in vitro inhibition effect toward CYP enzyme and hERG was observed in 9h; (2) The single-dose acute toxicity test did not induce mice death and obvious pathological damage; (3) Excellent oral bioavailability of 9h (F= 86%) in rats was unveiled. These results provide valuable guidance for further development of HEPT anti-HIV-1 drugs.

Broad-Spectrum Cyclopropane-Based Inhibitors of Coronavirus 3C-like Proteases: Biochemical, Structural, and Virological Studies

The advent of SARS-CoV-2, the causative agent of COVID-19, and its worldwide impact on global health, have provided the impetus for the development of effective countermeasures that can be deployed against the virus, including vaccines, monoclonal antibodies, and direct-acting antivirals (DAAs). Despite these efforts, the current paucity of DAAs has created an urgent need for the creation of an enhanced and diversified portfolio of broadly acting agents with different mechanisms of action that can effectively abrogate viral infection. SARS-CoV-2 3C-like protease (3CLpro), an enzyme essential for viral replication, is a validated target for the discovery of SARS-CoV-2 therapeutics. In this report, we describe the structure-guided utilization of the cyclopropane moiety in the design of highly potent inhibitors of SARS-CoV-2 3CLpro, SARS-CoV-1 3CLpro, and MERS-CoV 3CLpro. High-resolution cocrystal structures were used to identify the structural determinants associated with the binding of the inhibitors to the active site of the enzyme and unravel the mechanism of action. Aldehydes 5c and 11c inhibited SARS-CoV-2 replication with EC50 values of 12 and 11 nM, respectively. Furthermore, the corresponding aldehyde bisulfite adducts 5d and 11d were equipotent with EC50 values of 13 and 12 nM, respectively. The safety index (SI) values for compounds 5c / 11c and 5d / 11d ranged between 7692 and 9090. Importantly, aldehydes 5c / 11c and bisulfite adducts 5d / 11d potently inhibited MERS-CoV 3CLpro with IC50 values of 80 and 120 nM, and 70 and 70 nM, respectively. Likewise, compounds 5c / 11c and 5d / 11d inhibited SARS-CoV-1 with IC50 values of 960 and 350 nM and 790 and 240 nM, respectively. Taken together, these studies suggest that the inhibitors described herein have low cytotoxicity and high potency and are promising candidates for further development as broad-spectrum direct-acting antivirals against highly pathogenic coronaviruses.

The Solubility Studies and the Complexation Mechanism Investigations of Biologically Active Spiro[cyclopropane-1,3'-oxindoles] with β-Cyclodextrins

In this work, we first improved the aqueous solubility of biologically active spiro[cyclopropane-1,3′-oxindoles] (SCOs) via their complexation with different β-cyclodextrins (β-CDs) and proposed a possible mechanism of the complex formation. β-CDs significantly increased the water solubility of SCOs (up to fourfold). Moreover, the nature of the substituents in the β-CDs influenced the solubility of the guest molecule (MβCD > SBEβCD > HPβCD). Complexation preferably occurred via the inclusion of aromatic moieties of SCOs into the hydrophobic cavity of β-CDs by the numerous van der Waals contacts and formed stable supramolecular systems. The phase solubility technique and optical microscopy were used to determine the dissociation constants of the complexes (Kc~102 M−1) and reveal a significant decrease in the size of the formed crystals. FTIR-ATR microscopy, PXRD, and 1H-1H ROESY NMR measurements, as well as molecular modeling studies, were carried out to elucidate the host−guest interaction mechanism of the complexation. Additionally, in vitro experiments were carried out and revealed enhancements in the antibacterial activity of SCOs due to their complexation with β-CDs.

Umpolung Asymmetric 1,5-Conjugate Addition via Palladium Hydride Catalysis

Electronically matched nucleophilic 1,6-conjugate addition has been well studied and widely applied in synthetic areas. In contrast, nucleophilic 1,5-conjugate addition represents an electronically forbidden process and is considered unfeasible. Here, we describe modular protocols for 1,5-conjugate addition reactions via palladium hydride catalysis. Both palladium and synergistic Pd/organocatalyst systems are developed to catalyze 1,5-conjugate reaction, followed by inter- or intramolecular [3+2] cyclization. A migratory 1,5-addition protocol is established to corroborate the feasibility of this umpolung concept. The 1,5-addition products are conveniently transformed into a series of privileged enantioenriched motifs, including polysubstituted tetrahydrofuran, dihydrofuran, cyclopropane, cyclobutane, azetidine, oxetane, thietane, spirocycle and bridged rings. Preliminary mechanistic studies corroborate the involvement of palladium hydride catalysis.

Intermolecular Organophotocatalytic Cyclopropanation of Unactivated Olefins

Intermolecular cyclopropanation of mono-, di-, and trisubstituted olefins with α-bromo-β-ketoesters and α-bromomalonates under organophotocatalysis is reported. The reaction displays broad functional group tolerance, including substrates bearing acids, alcohols, halides, ethers, ketones, nitriles, esters, amides, carbamates, silanes, stannanes, boronic esters, as well as arenes, and furnishes highly substituted cyclopropanes. The transformation may be performed in the presence of air and moisture with 0.5 mol % of a benzothiazinoquinoxaline as organophotocatalyst. Mechanistic investigations, involving Stern-Volmer quenching, quantum yield determination, and deuteration experiments, are carried out, and a catalytic cycle for the transformation is discussed.

Imine Directed Cp*RhIII -Catalyzed N-H Functionalization and Annulation with Amino Amides, Aldehydes, and Diazo Compounds

A multicomponent annulation that proceeds by imine directed Cp*RhIII -catalyzed N-H functionalization is disclosed. The transformation affords piperazinones displaying a range of functionality and is the first example of transition metal-catalyzed multicomponent N-H functionalization. A broad range of readily available α-amino amides, including those derived from glycine, α-substituted, and α,α-disubstituted amino acids, were effective inputs and enabled the incorporation of a variety of amino acid side chains with minimal racemization. Branched and unbranched alkyl aldehydes and various stabilized diazo compounds were also efficient reactants. The piperazinone products were further modified through efficient transformations. Mechanistic studies, including X-ray crystallographic characterization of a catalytically competent five-membered rhodacycle with imine and amide nitrogen chelation, provide support for the proposed mechanism.

Cyclopropylcarbinyl cation chemistry in synthetic method development and natural product synthesis: cyclopropane formation and skeletal rearrangement

In this Review, the underrecognized utilities of the cyclopropylcarbinyl cation chemistry are summarized in cyclopropane synthesis and skeletal rearrangements, and their applications in natural product total synthesis are highlighted.

Engineered Myoglobin Catalysts for Asymmetric Intermolecular Cyclopropanation Reactions

Biocatalysis has covered an increasingly important role in the synthesis and manufacturing of pharmaceuticals and other high value compounds. In the interest of expanding the range of synthetically useful reactions accessible via biocatalysts, our group has explored the potential and application of engineered myoglobins for 'abiological' carbene transfer catalysis. These transformations provide a direct route for the construction of new carbon-carbon and carbon-heteroatom bonds, including the synthesis of cyclopropane rings, which are key motifs and pharmacophores in many drugs and bioactive natural products. In this award article, we survey the progress made by our group toward the development of myoglobin-based catalysts for asymmetric intermolecular cyclopropanation reactions. The high stereoselectivity exhibited by these biocatalysts in these reactions, combined with their broad substrate scope, scalability, and robustness to high substrate loading and organic co-solvents, contribute to make these systems particularly useful for chemical synthesis and biocatalysis at the preparative scale. Extension of the scope of biocatalytic carbene transfer reactions to include different classes of carbene donor reagents has created new opportunities for the asymmetric synthesis of functionalized cyclopropanes. Furthermore, the integration of myoglobin-catalyzed stereoselective cyclopropanations with chemical diversification of the enzymatic products has furnished attractive chemoenzymatic strategies to access a diverse range of optically active cyclopropane scaffolds of high value for drug discovery, medicinal chemistry, and the synthesis of natural products.

Skeletal Ring Contractions via I(I)/I(III) Catalysis: Stereoselective Synthesis of cis-α,α-Difluorocyclopropanes

The clinical success of α,α-difluorocyclopropanes, combined with limitations in the existing synthesis portfolio, inspired the development of an operationally simple, organocatalysis-based strategy to access cis-configured derivatives with high levels of stereoselectivity (up to >20:1 cis:trans). Leveraging an I(I)/I(III)-catalysis platform in the presence of an inexpensive HF source, it has been possible to exploit disubstituted bicyclobutanes (BCBs) as masked cyclobutene equivalents for this purpose. In situ generation of this strained alkene, enabled by Brønsted acid activation, facilitates an unprecedented 4 → 3 fluorinative ring contraction, to furnish cis-α,α-difluorinated cyclopropanes in a highly stereoselective manner (up to 88% yield). Mechanistic studies are disclosed together with conformational analysis (X-ray crystallography and NMR) to validate cis-α,α-difluorocyclopropanes as isosteres of the 1,4-dicarbonyl moiety. Given the importance of this unit in biology and the foundational n_o → π* interactions that manifest themselves in this conformation (e.g., collagen), it is envisaged that the title motif will find application in focused molecular design.

2-(Cyclopropylamino)-5-(4-methoxybenzylidene)thiazol-4(5H)-one

Multicomponent reactions effectively contribute to modern organic and medicinal chemistry. 4-Thiazolidinone core and cyclopropyl moiety are important structural motifs for design of potential biologically active molecules. In the present paper, the convenient step-economy and cost-effective synthesis of 2-(cyclopropylamino)-5-(4-methoxybenzylidene)thiazol-4(5H)-one (2) is described based on the application of the MCR methodology. The proposed approach includes direct one-pot interaction of 2-thioxothiazolidin-4-one (rhodanine), 4-methoxybenzaldehyde with cyclopropylamine which was used in 10% excess compare to other reagents. The structure of synthesized compound 2 was confirmed using 1H, 13C, 2D NMR, LC-MS, IR and UV spectra. The presence of prototropic amino/imino tautomerism for synthesized compound 2 was observed based on spectral analysis data. Screening of antimicrobial activity against 12 strains of Gram-positive and Gram-negative bacteria, as well as yeasts, was performed for synthesized derivative 2.

A Computational Study on the Mechanism of Catalytic Cyclopropanation Reaction with Cobalt N-Confused Porphyrin: The Effects of Inner Carbon and Intramolecular Axial Ligand

The factors that affect acceleration and high trans/cis selectivity in the catalytic cyclopropanation reaction of styrene with ethyl diazoacetate by cobalt N-confused porphyrin (NCP) complexes were investigated using density functional theory calculations. The reaction rate was primarily related to the energy gap between the cobalt–carbene adduct intermediates, A and B, which was affected by the NCP skeletons and axial pyridine ligands more than the corresponding porphyrin complex. In addition, high trans/cis stereoselectivity was determined at the TS1 and, in part, in the isomerization process at the carbon-centered radical intermediates, Ctrans and Ccis.

Base-promoted highly efficient synthesis of nitrile-substituted cyclopropanes via Michael-initiated ring closure

A convenient and efficient annulation reaction has been developed for the general synthesis of dinitrile-substituted cyclopropanes in moderate to excellent yields. A variety of 2-arylacetonitriles and α-bromoennitriles were compatible under the standard conditions. The reaction was achieved through tandem Michael-type addition followed by intramolecular cyclization. The preliminary application of this method was confirmed by the synthesis of the 2,4-dioxo-3-azabicyclo[3.1.0]hexane scaffold.

Modular Synthesis of Cyclopropane-Fused N-Heterocycles Enabled by Underexplored Diazo Reagents

Cyclopropane-fused N-heterocycles are featured in various biologically active compounds and represent attractive scaffolds in medicinal chemistry. However, synthesis routes to access structurally and functionally diverse cyclopropane-fused N-heterocycles remain underexplored. Leveraging novel α-diazo acylating agents, we report a general approach for the direct and modular synthesis of cyclopropane-fused lactams from unsaturated amines. The operationally simple transformation, which proceeds through successive acylation, (3+2) cycloaddition and fragmentation, tolerates a broad range of functional groups and yields a wide spectrum of complex molecular scaffolds, including fused, bridged and spiro ring systems. We demonstrate the utility of this transformation in the concise syntheses of therapeutic agents milnaciprane and amitifadine.

Nickel-Catalyzed Reductive Alkylation of Heteroaryl Imines

The preparation of heterobenzylic amines by a Ni-catalyzed reductive cross-coupling between heteroaryl imines and C(sp3 ) electrophiles is reported. This umpolung-type alkylation proceeds under mild conditions, avoids the pre-generation of organometallic reagents, and exhibits good functional group tolerance. Mechanistic studies are consistent with the imine substrate acting as a redox-active ligand upon coordination to a low-valent Ni center. The resulting bis(2-imino)heterocycle⋅Ni complexes can engage in alkylation reactions with a variety of C(sp3 ) electrophiles, giving heterobenzylic amine products in good yields.

Cyclopropane-Fused N-Heterocycles via Aza-Heck-Triggered C(sp3)-H Functionalization Cascades

Unique examples of aza-Heck-based C(sp³)–H functionalization cascades are described. Under Pd(0)-catalyzed conditions, the aza-Heck-type cyclization of N-(pentafluorobenzoyloxy)carbamates generates alkyl–Pd(II) intermediates that effect C(sp³)–H palladation en route to cyclopropanes. Key factors that control the site selectivity of the cyclopropanation process have been elucidated such that selective access to a wide range of ring- or spiro-fused systems can be achieved.

Design, synthesis, and structure-activity relationship of novel RIPK2 inhibitors

The NOD1/2 (nucleotide-binding oligomerization domain-containing protein 1/2) signaling pathways are involved in innate immune control and host defense. NOD dysfunction can result in a variety of autoimmune disorders. NOD-induced generation of inflammatory cytokines is mediated by receptor-interacting protein kinase 2 (RIPK2), which has been considered as a promising therapeutic target. Herein, we disclose the design, synthesis, and SAR study of a series of RIPK2 inhibitors. The lead compound 17 displayed a high affinity for RIPK2 (K_d = 5.9 nM) and was capable of inhibiting RIPK2 kinase function in an ADP-Glo assay. In vitro DMPK studies showed that compound 17 had good metabolic stability and no CYP inhibition. Compound 17 effectively suppressed inflammatory cytokine production in both cells and animal model.

Oxidative functionalization of alkylidenecyclopropanes and alkylidenecyclobutanes: a versatile platform to access nitrated cyclopropanes and cyclobutanes

A divergent radical nitration of alkylidenecyclopropanes (ACPs) and alkylidenecyclobutanes (ACBs) with Fe(NO₃)₃·9H₂O or AgNO₂ has been achieved, affording three categories of products including β-nitro alcohol, α-nitro ketone and nitro nitratosation products with yields up to 90%. Particularly, the cyclopropyl and cyclobutyl rings were conserved in the products. The applicability of this method was demonstrated by the scale-up experiment and reduction of the nitro into an amino group. Preliminary mechanistic studies suggested that the nitro radical was involved in the reaction process.

Control of Redox‐Active Ester Reactivity Enables a General Cross‐Electrophile Approach to Access Arylated Strained Rings**

Strained rings are increasingly important for the design of pharmaceutical candidates, but cross‐coupling of strained rings remains challenging. An attractive, but underdeveloped, approach to diverse functionalized carbocyclic and heterocyclic frameworks containing all‐carbon quaternary centers is the coupling of abundant strained‐ring carboxylic acids with abundant aryl halides. Herein we disclose the development of a nickel‐catalyzed cross‐electrophile approach that couples a variety of strained ring N‐hydroxyphthalimide (NHP) esters, derived from the carboxylic acid in one step, with various aryl and heteroaryl halides under reductive conditions. The chemistry is enabled by the discovery of methods to control NHP ester reactivity, by tuning the solvent or using modified NHP esters, and the discovery that ^t‐BuBpyCam^CN, an L2X ligand, avoids problematic side reactions. This method can be run in flow and in 96‐well plates.

Enantioselective Formation of All-Carbon Quaternary Stereocenters in gem-Difluorinated Cyclopropanes via Rhodium-Catalyzed Stereoablative Kinetic Resolution

Herein, we report an effective method to offer chiral gem-difluorinated cyclopropanes containing an all-carbon quaternary stereocenter by rhodium-catalyzed stereoablative kinetic resolution. The activation of a sterically hindered all-carbon quaternary C-C bond through oxidative addition with a chiral rhodium complex is proposed as the enantiodetermining step. A wide range of gem-difluorinated cyclopropanes can be obtained with excellent ee values (ee = 87% to >99.9%), which are demonstrated to be useful chiral fluorine-containing building blocks by a series of postfunctionalizations.

Efficient Synthesis of Orphaned Cyclopropanes Using Sulfones as Carbene Equivalents

Small molecules containing 1,1-dimethylcyclopropanes are prevalent throughout nature but are difficult to synthesize using state-of-the-art metal-catalyzed carbene transfer methods without competing 1,2-hydride shifts. Herein, we introduce a mechanistically distinct platform to transfer 1,1-dialkylcarbene units to olefins using carbometalation reactions of dialkyl sulfonyl anions. In the presence of NaNH₂ or n-BuLi in ethereal solvents, dialkyl sulfones react with styrenes and arylbutadienes between 23 and 70 °C to produce the corresponding 1,1-dialkylcyclopropanes. We report 40 examples of this reactivity including 16 different styrenes (up to 89% isolated yield), 9 arylbutadienes (51-88% yield), and 13 different sulfones (46-80% yield). In addition, we report an example of a sequential cyclopropanation reaction using this method. Preliminary mechanistic studies suggest a stepwise anionic process that is initiated by the direct addition of sulfonyl anions to a carbon-carbon double bond.

Synthesis of Vicinal Carbocycles by Intramolecular Nickel-Catalyzed Conjunctive Cross-Electrophile Coupling Reaction

A nickel-catalyzed intramolecular conjunctive cross-electrophile coupling reaction has been established. This method enables the synthesis of 3,5-vicinal carbocyclic rings found in numerous biologically active compounds and natural products. We provide mechanistic experiments that indicate this reaction proceeds through alkyl iodides formed in situ, initiates at the secondary electrophilic center, and proceeds through radical intermediates.

A substrate-dependent reaction of 1-aryl-2-alkyl-1,2-diketones with 2-aroyl-1-chlorocyclopropanecarboxylates: selective access to 2',5'-dicyclopropoxy-1,1':4',1''-teraryls and pentafulvenes

An interesting substrate-controlled one-pot approach to highly substituted 2',5'-dicyclopropoxy-1,1':4',1''-teraryls and 6-hydroxypentafulvenes involving various 1,2-diketones and 2-aroyl-1-chlorocyclopropanecarboxylates as 3C Michael acceptors triggered by Cs₂CO₃ has been developed. We noticed that 1,2-diketones play a decisive role in this reaction to determine the product's selectivity. For example, aryl rings having electron-poor functionalities at the para and meta-positions of 1,2-diketones led to 2,5-diarylhydroquinones selectively via a cyclodimerization/double oxa-Michael process with highly strained cyclopropenes. However, when 1-naphthyl/electron-donating aryl/ortho-aryl-substituted 1,2-diketones were chosen, the Michael-initiated ring expansion reaction (C-C and CC bonds) took place under the same conditions that gave the corresponding pentafulvenes predominately. Moreover, this reaction has several imperative features such as good to high diastereoselectivities, wide substrate scope, good functional group tolerance, transition metal-free process, etc.

Catalytic cyclopropanation reactions with α-silyl-, germanyl- and stannyl carbenes generated from cyclopropenes

Silylcyclopropenes are employed as precursors of α-silyl vinyl carbenes and trapped with alkenes. Cyclopropylsilanes were obtained in good yields with ample scope and complete regio- and diastereoselectivity. Stereoretentive protodesilylations enabled access to cis-1,2-disubstituted cyclopropanes. Cyclopropylstannanes and -germanes can also be prepared from the corresponding cyclopropenes.

Zinc-Mediated Transformation of 1,3-Diols to Cyclopropanes for Late-Stage Modification of Natural Products and Medicinal Agents

A method for incorporating cyclopropane motifs into complex molecules has been developed. Herein we report a zinc dust-mediated cross-electrophile coupling reaction of 1,3-dimesylates to synthesize cyclopropanes. 1,3-Dimesylates can be readily accessed from 1,3-diols, a functionality prevalent in many natural products and medicinal agents. The reaction conditions are mild, such that functional groups, including amides, esters, heterocycles, and alkenes, are tolerated. Notably, we have demonstrated late-stage cyclopropanation of statin medicinal agents.

Sulfoxonium Ylides in Aminocatalysis: An Enantioselective Entry to Cyclopropane-Fused Chromanol Structures

The 1,1a,2,7b-tetrahydrocyclopropa[c]chromene, arising from fusion of chromane and cyclopropane rings is the core of medicinally relevant compounds. Engaging sulfoxonium ylides in enantioselective aminocatalytic reactions for the first time, a convenient entry to this scaffold is presented. Several ring-fused derivatives were obtained in moderate-to-good yields and enantioselectivities and with perfect diastereoselectivity at the cyclopropane, using an α,α-diphenylprolinol aminocatalyst. The versatility of the hemiacetal moiety in the products was leveraged to effect various synthetic manipulations.