Enantioselective Cyclopropanation of a Wide Variety of Olefins Catalyzed by Ru(II)-Pheox Complexes

Enantioselective One-Pot Synthesis of Cyclopropane-Fused Tetrahydroquinolines via a Ru-Catalyzed Intramolecular Cyclopropanation

A highly enantioselective one-pot synthesis of cyclopropane-fused tetrahydroquinolines bearing carbonyl functionalities, which are difficult to synthesize using conventional methods, is reported. Employing readily accessible alkene-tethered anthranilaldehydes, hydrazone formation and subsequent Ru-catalyzed intramolecular cyclopropanation furnish the desired products in ≤87% yield and ≤95% ee under mild conditions. Various anthranilaldehydes, functionalized alkenes, and N-aryl sulfonyl groups are tolerated, and a series of synthetic transformations were conducted to demonstrate the practical utility.

Desymmetrization-Addition Reaction of Cyclopropenes to Imines via Synergistic Photoredox and Cobalt Catalysis

Herein, we designed a reaction for the desymmetrization-addition of cyclopropenes to imines by leveraging the synergy between photoredox and asymmetric cobalt catalysis. This protocol facilitated the synthesis of a series of chiral functionalized cyclopropanes with high yield, enantioselectivity, and diastereoselectivity (44 examples, up to 93% yield and >99% ee). A possible reaction mechanism involving cyclopropene desymmetrization by Co-H species and imine addition by Co-alkyl species was proposed. This study provides a novel route to important chiral cyclopropanes and extends the frontier of asymmetric metallaphotoredox catalysis.

Copper(I)-Catalyzed Indolyl Ynamide Oxidation/Dearomatization: Divergent and Regioselective Synthesis of Valuable Indoline Scaffolds

A highly convenient copper(I)-catalyzed oxidation-initiated cyclopropanation of indolyl ynamide for the rapid construction of indole-fused cyclopropane-lactams is described, which represents, to the best of our knowledge, the first non-noble-metal-catalyzed indolyl ynamide oxidation/dearomatization by the in situ generated α-oxo copper carbenes. Compared to hydrazone and diazo, the use of alkynes as carbene precursors allows cyclopropanation to occur under a safe and convenient pathway. Moreover, this transformation can lead to the divergent synthesis of pentacyclic spiroindolines involving the reversal of ynamide regioselectivity by engineering substrate structures.

Experimental and Computational Studies for the Synthesis of Functionalized Cyclopropanes from 2-Substituted Allylic Derivatives with Ethyl Diazoacetate

The catalytic asymmetric synthesis of highly functionalized cyclopropanes from 2-substituted allylic derivatives is reported. Using ethyl diazo acetate, the reaction, catalyzed by a chiral ruthenium complex (Ru(II)-Pheox), furnished the corresponding easily separable cis and trans cyclopropanes in moderate to high yields (32-97 %) and excellent ee (86-99 %). This approach significantly extends the portfolio of accessible enantioenriched cyclopropanes from an underexplored class of olefins. DFT calculations suggest that an outer-sphere mechanism is operative in this system.

Recent Synthetic Advances on the Use of Diazo Compounds Catalyzed by Metalloporphyrins

Diazo compounds are organic substances that are often used as precursors in organic synthesis like cyclization reactions, olefinations, cyclopropanations, cyclopropenations, rearrangements, and carbene or metallocarbene insertions into C-H, N-H, O-H, S-H, and Si-H bonds. Typically, reactions from diazo compounds are catalyzed by transition metals with various ligands that modulate the capacity and selectivity of the catalyst. These ligands can modify and enhance chemoselectivity in the substrate, regioselectivity and enantioselectivity by reflecting these preferences in the products. Porphyrins have been used as catalysts in several important reactions for organic synthesis and also in several medicinal applications. In the chemistry of diazo compounds, porphyrins are very efficient as catalysts when complexed with low-cost metals (e.g., Fe and Co) and, therefore, in recent years, this has been the subject of significant research. This review will summarize the advances in the studies involving the field of diazo compounds catalyzed by metalloporphyrins (M-Porph, M = Fe, Ru, Os, Co, Rh, Ir) in the last five years to provide a clear overview and possible opportunities for future applications. Also, at the end of this review, the properties of artificial metalloenzymes and hemoproteins as biocatalysts for a broad range of applications, namely those concerning carbene-transfer reactions, will be considered.

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.

Ruthenium complexes of 1,4-diazabutadiene ligands with a cis-RuCl2 moiety for catalytic acceptorless dehydrogenation of alcohols: DFT evidence of chemically non-innocent ligand participation

The acceptorless dehydrogenative coupling (ADC) of primary alcohols to esters by diazabutadiene-coordinated ruthenium compounds is reported. Treatment of cis-Ru(dmso)4Cl2 in acetone at 56 °C with different 1,4-diazabutadienes [p-XC6H4N[double bond, length as m-dash]C(H)(H)C[double bond, length as m-dash]NC6H4X-p; X = H, CH3, OCH3, and Cl; abbreviated as DAB-X], gives trans-Ru[κ2-N,N-DAB-X]2Cl2 as the kinetic product of substitution. Heating these products in o-xylene at 144 °C gives the thermodynamically favored cis-Ru[κ2-N,N-DAB-X]2Cl2 isomers. Electronic structure calculations confirm the greater stability of the cis diastereomer. The molecular structures for each pair of geometric isomers have been determined by X-ray diffraction analyses. Cyclic voltammetry experiments on the complexes show an oxidative response and a reductive response within 0.50 to 0.93 V and -0.76 to -1.24 V vs. SCE respectively. The cis-Ru[κ2-N,N-DAB-X]2Cl2 complexes function as catalyst precursors for the acceptorless dehydrogenative coupling of primary alcohols to H2 and homo- and cross-coupled esters. When 1,4-butanediol and 1,5-pentanediol are employed as substrates, lactones and hydroxyaldehydes are produced as the major dehydrogenation products, while secondary alcohols afforded ketones in excellent yields. The mechanism for the dehydrogenation of benzyl alcohol to benzyl benzoate and H2 using cis-Ru[κ2-N,N-DAB-H]2Cl2 (cis-1) as a catalyst precursor was investigated by DFT calculations. The data support a catalytic cycle that involves the four-coordinate species Ru[κ2-N,N-DAB-H][κ1-N-DAB-H](κ1-OCH2Ph) whose protonated κ1-diazabutadiene moiety functions as a chemically non-innocent ligand that facilitates a β-hydrogen elimination from the κ1-O-benzoxide ligand to give the corresponding hydride HRu[κ2-N,N-DAB-H][κ1-N-DAB-H](κ2-O,C-benzaldehyde). H2 production follows a Noyori-type elimination to give (H2)Ru[κ2-N,N-DAB-H][κ1-N-DAB-H](κ1-O-benzaldehyde) as an intermediate in the catalytic cycle.

An Intramolecular Umpolung Cascade Kukhtin-Ramirez Reaction/Michael Addition-Initiated Cyclization: Stereoselective Synthesis of Tetrasubstituted Cyclopropane Fused 1-Indanones

Herein, we disclose a fascinating highly stereoselective P(NMe₂)₃ mediated intramolecular deoxygenative umpolung cascade Michael addition-initiated cyclopropanation with a diverse substrate adaptability. This methodology creates a new horizon for expedient access to valuable 6,5,3-fused scaffolds having an all-carbon quaternary stereocenter via Kukhtin-Ramirez (K-R) adduct formation, with excellent diastereoselectivity and yields under metal-free ambient conditions. A few functional group transformations have also been performed successfully. Additionally, an asymmetric catalytic attempt using (R)-(+)-H8-BINOL has delivered good enantioselectivity.

Low Coordination State RhI -Complex as High Performance Catalyst for Asymmetric Intramolecular Cyclopropanation: Construction of penta-Substituted Cyclopropanes

A simple, broad-scope rhodium(I)/chiral diene catalytic system for challenging asymmetric intramolecular cyclopropanation of various tri-substituted allylic diazoacetates was successfully developed. The low coordination state Rh^I -complex exhibits an extraordinarily high degree of tolerance to the variation in the extent of substitution of the allyl double bond, thus allowing the efficient construction of a wide range of penta-substituted, fused-ring cyclopropanes bearing three contiguous stereogenic centers, including two quaternary carbon stereocenters, in a highly enantioselective manner with ease at catalyst loading as low as 0.1 mol %. The stereoinduction mode of this Rh^I -carbene-directed asymmetric intramolecular cyclopropanation was investigated by DFT calculations, indicating that π-π stacking interactions between the aromatic rings of chiral diene ligand and diazo substrate play a key role in the control of the reaction enantioselectivity.

Asymmetric Synthesis of Chiral Cyclopropanes from Sulfoxonium Ylides Catalyzed by a Chiral-at-Metal Rh(III) Complex

An enantioselective cyclopropanation reaction of sulfoxonium ylides with β,γ-unsaturated ketoesters catalyzed by a chiral rhodium catalyst has been realized. A variety of optically pure 1,2,3-trisubstituted cyclopropanes was synthesized in 48-89% yields, with up to 99% ee, and with dr >20:1. Furthermore, research shows that a weak coordination between the chiral rhodium catalyst and β,γ-unsaturated ketoesters was responsible for the high diastereoselectivity and enantioselectivity of the corresponding products.

Base-Catalyzed Traceless Silylation and Deoxygenative Cyclization of Chalcones to Cyclopropanes

Development of simple synthetic methods from readily available compounds to complex products is of utmost interest in modern synthesis. Catalytic synthesis of cyclopropanes is important for diverse chemical applications. We present a method for the transformation of readily accessible α,β-unsaturated ketones (chalcones) to cyclopropanes. A simple base, KOH, catalyzed the selective reduction of the enone carbonyl functionality, dehydrogenative silylation, and deoxygenative cyclization of chalcones to provide the cyclopropane products. Chalcones with extended conjugation and 4-chromanone-based substrates also provided the corresponding cyclopropanes. One-pot synthesis of cyclopropanes directly from industrial feedstock compounds such as ketones and aldehydes is also demonstrated using catalytic KOH for both intermolecular condensation and dehydrogenative silylation-deoxygenative intramolecular cyclization cascade.

DFT Mechanistic Study of the Cyclopropanation of Styrene and Aryldiazodiacetate Catalyzed by Tris(pentafluorophenyl)borane

Metal-free boron Lewis acids, tris(pentafluorophenyl)borane B(C₆F₅)₃, have the advantages of low toxicity and low cost and are a promising catalyst. A density functional theory (DFT) calculation was used to clarify the mechanism and the origin of the diastereoselective cyclopropanation of aryldiazodiacetate and styrene derivatives catalyzed by B(C₆F₅)₃. Four pathways were calculated: B(C₆F₅)₃-catalyzed N-, C-, and O-bound boron-activated aryldiazodiacetate and without B(C₆F₅)₃ catalysis. By calculating and comparing the energy barriers, the most possible reaction mechanism was proposed, that is, first, B(C₆F₅)₃ catalyzed O-bound boron to activate aryldiazodiacetate, followed by the removal of a N₂ molecule, and finally, styrene nucleophilic attack occurred to produce [2+1] cyclopropane products. N₂ removal is the rate-limiting step, and this step determines the preference of a given mechanism. The calculated results are in agreement with experimental observations. The origin of diastereoselectivity is further explained on the basis of the favorable mechanism. The steric hindrance interference between the styrene aryl group and the large tri(pentafluorophenyl)borane B(C₆F₅)₃ and the favorable π-π stacking interaction between the benzene rings combined to cause the high diastereoselectivity, which resulted in lower energy of the transition state (TS) corresponding to the reaction mechanism. The calculated results not only provide a more detailed explanation of the mechanism for the experimental study but also have certain reference and guiding significance for other catalytic cyclopropanation reactions.

From Serendipity to Rational Design: Heteroleptic Dirhodium Amidate Complexes for Diastereodivergent Asymmetric Cyclopropanation

A heteroleptic dirhodium paddlewheel complex comprising three chiral carboxylate ligands and one achiral acetamidate ligand has recently been found to be uniquely effective in catalyzing the asymmetric cyclopropanation of olefins with α-stannylated (silylated and germylated) α-diazoacetate derivatives. A number of control experiments in combination with detailed computational studies provide compelling evidence that an interligand hydrogen bond between the −NH group of the amidate and the ester carbonyl group of the reactive rhodium carbene intermediate plays a quintessential role in the stereodetermining transition state. The penalty for distorting this array outweighs steric arguments and renders two of the four conceivable transitions states unviable. Based on this mechanistic insight, the design of the parent catalyst is revisited herein: placement of appropriate peripheral substituents allows high levels of diastereocontrol to be imposed upon cyclopropanation, which the original catalyst lacks. Because the new complexes allow either trans- or cis-configured stannylated cyclopropanes to be made selectively and in excellent optical purity, this transformation also marks a rare case of diastereodivergent asymmetric catalysis. The products are amenable to stereospecific cross coupling with aryl halides or alkenyl triflates; these transformations appear to be the first examples of the formation of stereogenic quaternary carbon centers by the Stille reaction; carbonylative coupling is also achieved. Moreover, tin/lithium exchange affords chiral lithium enolates, which can be intercepted with a variety of electrophilic partners. The virtues and inherent flexibility of this new methodology are illustrated by an efficient synthesis of two salinilactones, extremely scarce bacterial metabolites with signaling function involved in the self-regulatory growth inhibition of the producing strain.

Catalysis with cycloruthenated complexes

Cycloruthenated complexes have been studied extensively over the last few decades. Many accounts of their synthesis, characterisation, and catalytic activity in a wide variety of transformations have been reported to date. Compared with their non-cyclometallated analogues, cycloruthenated complexes may display enhanced catalytic activities in known transformations or possess entirely new reactivity. In other instances, these complexes can be chiral, and capable of catalysing stereoselective reactions. In this review, we aim to highlight the catalytic applications of cycloruthenated complexes in organic synthesis, emphasising the recent advancements in this field.

We discuss recent advances in the applications of cycloruthenated complexes in organic synthesis, comprising C–H activation, chiral-at-metal catalysis, Z-selective olefin metathesis, transfer hydrogenation, enantioselective cyclopropanations and cycloadditions.

Fluorocyclopropane-Containing Proline Analogue: Synthesis and Conformation of an Item in the Peptide Chemist's Toolbox

Over the years, numerous modifications to the structure of proline have been made in order to tune its effects on bioactive compounds. Notably, the introduction of a cyclopropane ring or a fluorine atom has produced interesting results. Herein, we describe the synthesis of a proline containing fluorocyclopropane. This modified amino acid was inserted into a tripeptide, whose conformation was studied by nuclear magnetic resonance and density functional theory calculations.

Enantioselective Synthesis of α-Aryl-β-Aminocyclopropane Carboxylic Acid Derivatives via Rh(II)-Catalyzed Cyclopropanation of Vinylsulfonamides with α-Aryldiazoesters

The reaction of vinylsulfonamides with donor-acceptor carbenes derived from α-aryldiazoesters, catalyzed by the tert-butyl glycine-derived dirhodium complex Rh₂(S-4-Br-NTTL)₄, has been reported. This method provides a variety of α-aryl-β-aminocyclopropane carboxylic acid derivatives bearing one quaternary carbon stereogenic center vicinal to the amino-substituted carbon in high yields with excellent diastereo- and enantioselectivities. Vinylsulfonamides showed complementary advantages over the well-developed vinylamides or vinylcarbamates for this Rh(II)-catalyzed cyclopropanation strategy. Moreover, these conformationally restricted α-aryl-β-aminocyclopropyl carboxylic acid derivatives can be readily incorporated into dipeptides.

Visible Light Induced Brønsted Acid Assisted Pd-Catalyzed Alkyl Heck Reaction of Diazo Compounds and N-Tosylhydrazones

A mild visible light-induced palladium-catalyzed alkyl Heck reaction of diazo compounds and N-tosylhydrazones is reported. A broad range of vinyl arenes and heteroarenes with high functional group tolerance, as well as a range of different diazo compounds, can efficiently undergo this transformation. This method features Brønsted acid-assisted generation of hybrid palladium C(sp3 )-centered radical intermediate, which allowed for new selective C-H functionalization protocol.

Highly stereoselective synthesis of spirocyclopropylthiooxindoles and biological evaluation

We present a novel highly stereoselective Rh-catalyzed cyclopropanation of diazothiooxindoles with a broad range of α-functionalized styrenes, enabling facile access of chiral spirocyclopropylthiooxindoles in high to excellent enantiomeric excess.

Highly enantioselective synthesis of norcaradiene derivatives from naphthyl diazoacetamides using a Ru(ii)-Pheox complex

The highly regio- and enantioselective intramolecular cyclopropanation reactions of naphthyl diazoacetamides have been reported herein.

Developments in the Catalytic Asymmetric Synthesis of Agrochemicals and Their Synthetic Importance

Catalytic asymmetric synthesis has become an essential tool for the enantioselective synthesis of pharmaceuticals, natural products, and agrochemicals (mainly fungicides, herbicides, insecticides, and pheromones). With continuous growing interest in both modern agricultural chemistry and catalytic asymmetric synthesis chemistry, this review provides a comprehensive overview of some earlier reports as well as the recent successful applications of various catalytic asymmetric syntheses methodologies, such as enantioselective hydroformylation, enantioselective hydrogenation, asymmetric Sharpless epoxidation and dihydroxylation, asymmetric cyclopropanation or isomerization, organocatalyzed asymmetric synthesis, and so forth, which have been used as key steps in the preparation of chiral agrochemicals (on R&D, piloting, and commercial scales). Chiral agrochemicals can also lead the new generation of such chemicals having specific and novel modes of action for achieving sustainable crop protection and production. Some perspectives and challenges for these catalytic asymmetric methodologies in the synthesis of chiral agrochemicals are also briefly discussed in the final section of the manuscript. This review will provide the insight regarding understanding, development, and evaluation of catalytic asymmetric systems for the synthesis of chiral agrochemicals among the agrochemists.

Stereodivergent Synthesis of Biologically Active Spironucleoside Scaffolds via Catalytic Cyclopropanation of 4-exo-Methylene Furanosides

Cyclopropane fusion of the only rotatable carbon-carbon bond in furanosyl nucleosides (i.e., exocyclic 4'-5') is a powerful design strategy to arrive at conformationally constrained analogues. Herein, we report a direct stereodivergent route toward the synthesis of the four possible configurations of 4-spirocyclopropane furanoses, which have been transformed into the corresponding 4'-spirocyclic adenosine analogues. The latter showed differential inhibition of the protein methyltransferase PRMT5-MEP50 complex, with one analogue inhibiting more effectively than adenosine itself, demonstrating the utility of rationally probing 4'-5' side chain orientations.

Asymmetric Total Synthesis of Shagenes A and B

We report the first total synthesis of shagenes A and B, which are tricyclic terpenoids containing a cis-substituted cyclopropane, via ring-closing metathesis of an enamide and Ir-catalyzed double-bond isomerization of an alkylidenecyclopropane. Chemo- and diastereoselectivity in the distorted cis-substituted structures were controlled by the alkylidenecyclopropane reactivity and using the ketone functionality as a remote directing group for the Ir catalyst, respectively. The total synthesis suggested the absolute configuration of shagenes.

Copper-catalyzed [3 + 1] cyclization of cyclopropenes/diazo compounds and bromodifluoroacetamides: facile synthesis of α,α-difluoro-β-lactam derivatives

We have developed a novel copper-catalyzed cyclization of cyclopropenes/diazo compounds and bromodifluoroacetamides, efficiently synthesizing a series of α,α-difluoro-β-lactams in moderate to excellent yields under mild reaction conditions. This reaction represents the first example of [3 + 1] cyclization for the synthesis of β-lactams utilizing a metal carbene intermediate as the C1 synthon.

A copper-catalyzed [3 + 1] cyclization of cyclopropenes and bromodifluoroacetamides/diazo compounds has been successfully developed, efficiently synthesizing a wide range of α,α-difluoro-β-lactams.

Combined Experimental and Computational Study of Ruthenium N-Hydroxyphthalimidoyl Carbenes in Alkene Cyclopropanation Reactions

A combined experimental-computational approach has been used to study the cyclopropanation reaction of N-hydroxyphthalimide diazoacetate (NHPI-DA) with various olefins, catalyzed by a ruthenium-phenyloxazoline (Ru-Pheox) complex. Kinetic studies show that the better selectivity of the employed redox-active NHPI diazoacetate is a result of a much slower dimerization reaction compared to aliphatic diazoacetates. Density functional theory calculations reveal that several reactions can take place with similar energy barriers, namely, dimerization of the NHPI diazoacetate, cyclopropanation (inner-sphere and outer-sphere), and a previously unrecognized migratory insertion of the carbene into the phenyloxazoline ligand. The calculations show that the migratory insertion reaction yields an unconsidered ruthenium complex that is catalytically competent for both the dimerization and cyclopropanation, and its relevance is assessed experimentally. The stereoselectivity of the reaction is argued to stem from an intricate balance between the various mechanistic scenarios.

Generation of Diazomethyl Radicals by Hydrogen Atom Abstraction and Their Cycloaddition with Alkenes

A general catalytic methodology for the synthesis of pyrazolines from α-diazo compounds and conjugated alkenes is reported. The direct hydrogen atom transfer (HAT) process of α-diazo compounds promoted by the tert-butylperoxy radical generates electrophilic diazomethyl radicals, thereby reversing the reactivity of the carbon atom attached with the diazo group. The regiocontrolled addition of diazomethyl radicals to carbon-carbon double bonds followed by intramolecular ring closure on the terminal diazo nitrogen and tautomerization affords a diverse set of pyrazolines in good yields with excellent regioselectivity. This strategy overcomes the limitations of electron-deficient alkenes in traditional dipolar [3+2]-cycloaddition of α-diazo compounds with alkenes. Furthermore, the straightforward formation of the diazomethyl radicals provides umpolung reactivity, thus opening new opportunities for the versatile transformations of diazo compounds.

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).

Ruthenium-Catalyzed Cycloadditions to Form Five-, Six-, and Seven-Membered Rings

Ruthenium-catalyzed cycloadditions to form five-, six-, and seven-membered rings are summarized, including applications in natural product total synthesis. Content is organized by ring size and reaction type. Coverage is limited to processes that involve formation of at least one C-C bond. Processes that are stoichiometric in ruthenium or exploit ruthenium as a Lewis acid (without intervention of organometallic intermediates), ring formations that occur through dehydrogenative condensation-reduction, σ-bond activation-initiated annulations that do not result in net reduction of bond multiplicity, and photochemically promoted ruthenium-catalyzed cycloadditions are not covered.

Well-Defined, Versatile and Recyclable Half-Sandwich Nickelacarborane Catalyst for Selective Carbene-Transfer Reactions

Catalytic carbene-transfer reactions constitute a class of highly useful transformations in organic synthesis. Although catalysts based on a range of transition-metals have been reported, the readily accessible nickel(II)-based complexes have been rarely used. Herein, an air-stable nickel(II)-carborane complex is reported as a well-defined, versatile and recyclable catalyst for selective carbene transfer reactions with low catalyst loading under mild conditions. This catalyst is effective for several types of reactions including diastereoselective cyclopropanation, epoxidation, selective X-H insertions (X = C, N, O, S, Si), particularly for the unprotected substrates. This represents a rare example of carborane ligands in base metal catalysis.

Copper(I)-Catalyzed Enyne Oxidation/Cyclopropanation: Divergent and Enantioselective Synthesis of Cyclopropanes

An efficient copper(I)-catalyzed enyne oxidation/cyclopropanation for the modular synthesis of cyclopropane derivatives is described, which represents the first non-noble metal-catalyzed enynes oxidation/cyclopropanation by the in situ generated α-oxo copper carbenes. This protocol allows the assembly of valuable cyclopropane-γ-lactams in generally good to excellent yields with excellent diastereoselectivity. More significantly, the enantioselective version of enyne oxidation/cyclopropanation has been disclosed with chiral copper catalysts.

Stereospecific Reactions Leading to Allylboronic Esters Within Acyclic Systems Bearing Distant Stereocenters

The preparation of acyclic molecules featuring congested stereocenters in a 1,4-relationship in only three catalytic steps from commercially available building blocks is reported. This approach involves a diastereoselective diboration of alkenyl cyclopropyl methanol derivatives followed by a regioselective exergonic ring fragmentation. The starting materials can be prepared enantiomerically enriched and all substituents can be interconverted, therefore, this strategy allows a large variety of diversely functionalized allylboronic esters possessing distant tetrasubstituted stereocenters with high diastereoselectivity.