Efficient Synthesis of β-CF3/SCF3-Substituted Carbonyls via Copper-Catalyzed Electrophilic Ring-Opening Cross-Coupling of Cyclopropanols

Promoting Catalytic C-Selective Sulfonylation of Cyclopropanols against Conventional O-Sulfonylation Using Readily Available Sulfonyl Chlorides

Against the backdrop of the well-known O-sulfonylation of cyclopropyl alcohols with sulfonyl chlorides, we examined the feasibility of conducting regioselective C-sulfonylation. By emulating an umpolung strategy-guided design, we report for the first time the Cu(II)-catalyzed β-sulfonylation of cyclopropanols by a mechanism that potentially involves an oxidative addition of a sulfonyl radical to a metal homoenolate. Unlike reported methods, this protocol allows a practical synthetic route to γ-keto sulfone building blocks from cyclopropanols by leveraging commercially available aryl- and alkyl-sulfonyl chlorides, common reagents in organic chemistry laboratories. Using operationally simple open-flask conditions, the preparative scope of starting materials was demonstrated using an array of aryl- and alkyl-substituted sulfonyl chlorides and cyclopropanols (43 examples, up to 96% yield).

Divergent Synthesis of β-Fluoroamides via Silver-Catalyzed Oxidative Deconstruction of Cyclopropanone Hemiaminals

An expedient approach for the synthesis of challenging β-fluoroamides from readily accessible cyclopropanone equivalents is reported. Following the addition of pyrazole used here as a transient leaving group, silver-catalyzed regiospecific ring-opening fluorination of the resulting hemiaminal leads to a β-fluorinated N-acylpyrazole intermediate reactive to substitution with amines, ultimately affording β-fluoroamides. The process could also be extended to the synthesis of β-fluoroesters and γ-fluoroalcohols via the addition of alcohols or hydrides as terminal nucleophiles, respectively.

Copper-catalyzed ring-opening trifluoromethylthiolation/trifluoromethylselenolation of cyclopropanols with TsSCF3 or Se-(trifluoromethyl) 4-methoxybenzenesulfonoselenoate

We report a ring-opening trifluoromethylthiolation of cyclopropanols with TsSCF₃ by using Cu(OAc)₂ as the catalyst. Moreover, by using this strategy, the trifluoromethylselenolation of cyclopropanols with Se-(trifluoromethyl) 4-methoxybenzenesulfonoselenoate to access β-SeCF₃-substituted carbonyl compounds is achieved for the first time. The broad substrate scope, readily accessible reagents and cheap catalyst make this protocol an alternative and efficient method for the synthesis of β-SCF₃-substituted or β-SeCF₃-substituted carbonyl compounds.

A Toolbox of Reagents for Trifluoromethylthiolation: From Serendipitous Findings to Rational Design

Two types of electrophilic trifluoromethylthiolating reagents were developed in the past 10 years in our laboratory. The development of the first type of reagent, trifluoromethanesulfenate I, which is highly reactive toward a variety of nucleophiles, was based on an unexpected discovery in the initial design for the development of an electrophilic trifluoromethylthiolating reagent with a hypervalent iodine skeleton. A structure-activity study disclosed that α-cumyl trifluoromethanesulfenate (reagent II) without the iodo substituent is equally effective. Subsequent derivatization let us develop an α-cumyl bromodifluoromethanesulfenate III that could be used for the preparation of [¹⁸F]ArSCF₃. To remediate the low reactivity of the type I electrophilic trifluoromethylthiolating reagent for Friedel-Crafts trifluoromethylthiolation of electron-rich (hetero)arenes, we designed and prepared N-trifluoromethylthiosaccharin IV, which exhibits broad reactivity toward various nucleophiles, including electron-rich arenes. A comparison of the structure of N-trifluoromethylthiosaccharin IV with that of N-trifluoromethylthiophthalimide showed that the replacement of one carbonyl group in N-trifluoromethylthiophthalimide with a sulfonyl group made N-trifluoromethylthiosaccharin IV much more electrophilic. Thus, the replacement of both carbonyls with two sulfonyl groups would further increase the electrophilicity. Such a rationale prompted us to design and develop the current most electrophilic trifluoromethylthiolating reagent, N-trifluoromethylthiodibenzenesulfonimide V, and its reactivity was much higher than that of N-trifluoromethylthiosaccharin IV. We further developed an optically pure electrophilic trifluoromethylthiolating reagent, (1S)-(-)-N-trifluoromethylthio-2,10-camphorsultam VI, for the preparation of optically active trifluoromethylthio-substituted carbon stereogenic centers. Reagents I-VI now constitute a powerful toolbox for the introduction of the trifluoromethylthio group into the target molecules.

Trifluoromethylation of Carbonyl and Unactivated Olefin Derivatives by C(sp3 )-C Bond Cleavage

Herein, we report a Cu-mediated trifluoromethylation of carbonyl-type compounds and unactivated olefins enabled by visible-light irradiation via σ C(sp³ )-C bond-functionalization. The reaction is distinguished by its modularity, mild conditions and wide scope-even in the context of late-stage functionalization-thus offering a complementary approach en route to valuable C(sp³ )-CF₃ architectures from easily accessible precursors.

Electrophilic Hydrazination of Cyclopropanols Using Azodicarboxylates via Copper(II) Catalysis: An Umpolung Strategy to Access β-Hydrazino Ketone Motifs

The scope of an umpolung approach to expand synthetic access to bifunctional γ-keto hydrazine intermediates via electrophilic amination of β-homoenolates derived from cyclopropanol precursors that took advantage of azodicarboxylates or azodicarboxamides as electron-deficient nitrogen sources was examined. This new synthetic procedure avails commercially available or readily accessible starting materials along with a ligand-free Cu(II) salt as an inexpensive catalyst. Using this operationally simple reaction, which proceeds under mild conditions (open-flask and ambient temperature) and is suitable for multigram scale, preparative applications were established with a range of aryl- and alkyl-substituted cyclopropanols and azodicarboxylate/azodicarboxamide substrates (26 examples, 74-95% yields). Further, the obtained products have been shown to provide convenient synthetic access to γ-hydroxy hydrazide, γ-amino hydrazide, and heterocyclic derivatives.

Palladium-Catalyzed Stagewise Strain-Release-Driven C-C Activation of Bicyclo[1.1.1]pentanyl Alcohols

A palladium-catalyzed chemoselective coupling of readily available bicyclo[1.1.1]pentanyl alcohols (BCP-OH) with various halides is reported, which offers expedient approaches to a wide range of cyclobutanone and β,γ-enone skeletons via single or double C-C activation. The chemistry shows a broad substrate scope in terms of both the range of BCP-OH and halides including a series of natural product derivatives. Moreover, dependency of reaction chemodivergence on base additive has been investigated through experimental and density functional theory (DFT) studies, which is expected to significantly enrich the reaction modes and increase the synthetic potential of BCP-OH in preparing more complex molecules.

Nickel-Catalyzed Carbonylation of Cyclopropanol with Benzyl Bromide for Multisubstituted Cyclopentenone Synthesis

Herein, we reported a Ni-catalyzed carbonylation of cyclopropanol with benzyl bromide to afford multisubstituted cyclopentenone under 1 atm of CO. The reaction proceeds through cascade carbonylation of benzyl bromides, followed by generation of nickel homoenolate from cyclopropanols via β-C elimination to afford 1,4-diketones, which undergoes intramolecular Aldol condensation to furnish highly substituted cyclopentenone derivatives in moderate to good yields. The reaction exhibits high functional group tolerance with broad substrate scope.

Orchestrating a β-Hydride Elimination Pathway in Palladium(II)-Catalyzed Arylation/Alkenylation of Cyclopropanols Using Organoboron Reagents

The scope of chemoselective β-hydride elimination in the context of arylation/alkenylation of homoenolates from cyclopropanol precursors using organoboronic reagents as transmetalation coupling partners was examined. The reaction optimization paradigm revealed a simple ligand-free Pd(II) catalytic system to be most efficient under open air conditions. The preparative scope, which was investigated with 48 examples, supported the applicability of this reaction to a wide range of substrates tolerating a variety of functional groups while delivering β-substituted enone and dienone derivatives in 62-95% yields.

Palladium-catalyzed selective C-C bond cleavage and stereoselective alkenylation between cyclopropanol and 1,3-diyne: one-step synthesis of diverse conjugated enynes

The stereoselective synthesis of 1,3-enynes from 1,3-diynes is demonstrated by palladium-catalyzed selective C–C bond cleavage of cyclopropanol. Exclusive formation of mono-alkenylated adducts was achieved by eliminating the possibility of di-functionalization with high stereoselectivity. Indeed, this protocol worked very well with electronically and sterically diverse substrates. Several studies, including deuterium labeling experiments and intermolecular competitive experiments, were carried out to understand the mechanistic details. The atomic-level mechanism followed in the catalytic process was also validated using DFT calculations, and the rate-controlling states in the catalytic cycle were identified. Furthermore, preliminary mechanistic investigations with radical scavengers revealed the non-involvement of the radical pathway in this transformation.

Palladium-catalyzed tandem activation and functionalization of readily accessible cyclopropanols have been demonstrated to access valuable conjugated enynes from 1,3-diynes with high stereo-selectivity.

Catalytic Net Oxidative C-C Activation and Silylation of Cyclopropanols with a Traceless Acetal Directing Group

Redox-neutral carbon-carbon (C-C) bond activation and functionalization strategies of cyclopropanols that give metallo homoenolate have offered merits to construct a range of useful β-functionalized ketones in an inverse-polarity fashion. Discovery and identification of oxidative C-C activation reactions of cyclopropanols that generate metallo enolate-homoenolate would provide an opportunity to afford α,β-difunctionalized ketones. We report catalytic, net oxidative C-C activation, and silylation of cyclopropanols with traceless acetal directing groups under consecutive Ir and Rh catalysis in regio-, stereo-, and chemo-selective fashion. In detail, Ir-catalyzed hydrosilylation of cyclopropyl acetates provides the acetal directing group in quantitative yield. Rh-catalyzed proximal C-C silylation of the resulting cyclopropyl silyl acetal produces the metallo enolate-homoenolate equivalent, dioxasilepine, which uniquely holds an interconnected β-silyl moiety and Z-vinyl acetal. Upon sequential treatment of a silaphile that removes the acetal directing group and electrophile, the seven-membered silicon-containing heterocycle, serving as the ketone α,β-dianion equivalent, delivers α,β-difunctionalized ketones. Scope of the hitherto unexplored reactivity of cyclopropanols toward net oxidative C-C silylation and the versatility of the resulting dioxasilepines were demonstrated. These include late-stage, net oxidative C-C silylation of biologically relevant molecules and facile production of a range of α,β-difunctionalized ketones. Preliminary mechanistic studies suggest that the C-C activation harnessing the electron-rich Wilkinson-type catalyst is likely the turnover-determining step and a Rh-π interaction is the key to the efficient metal insertion to the proximal C-C bond in cyclopropanols.

Palladium-Catalyzed Siloxycyclopropanation of Alkenes Using Acylsilanes

Currently, catalytically transferable carbenes are limited to electron-deficient and neutral derivatives, and electron-rich carbenes bearing an alkoxy group (i.e., Fischer-type carbenes) cannot be used in catalytic cyclopropanation because of the lack of appropriate carbene precursors. We report herein that acylsilanes can serve as a source of electron-rich carbenes under palladium catalysis, enabling cyclopropanation of a range of alkenes. This reactivity profile is in sharp contrast to that of metal-free siloxycarbenes, which are unreactive toward normal alkenes. The resulting siloxycyclopropanes serve as valuable homoenolate equivalents, allowing rapid access to elaborate β-functionalized ketones.

Asymmetric β-Arylation of Cyclopropanols Enabled by Photoredox and Nickel Dual Catalysis

The enantioselective functionalization and transformation of readily available cyclopropyl compounds are synthetically appealing yet challenging topics in organic synthesis. Here we report an asymmetric β-arylation of cyclopropanols with aryl bromides...

Iron catalyzed tandem ring opening/1,6-conjugate addition of cyclopropanols with p-quinone methides: new access to γ,γ-diaryl ketones

An iron(III) catalyzed tandem ring opening/1,6-conjugate addition of cyclopropanols to p-quinone methides leading to γ,γ-diaryl ketones has been described. This catalytic protocol provides a novel and efficient method to access γ,γ-diaryl ketone derivatives in good to excellent yields with high functional group tolerance. Importantly, γ,γ-diaryl ketone can be further functionalized to give a versatile set of useful products.

Catalytic Asymmetric Allylic Substitution with Copper(I) Homoenolates Generated from Cyclopropanols

By using copper(I) homoenolates as nucleophiles, which are generated through the ring-opening of 1-substituted cyclopropane-1-ols, a catalytic asymmetric allylic substitution with allyl phosphates is achieved in high to excellent yields with high enantioselectivity. Both 1-substituted cyclopropane-1-ols and allylic phosphates enjoy broad substrate scopes. Remarkably, various functional groups, such as ether, ester, tosylate, imide, alcohol, nitro, and carbamate are well tolerated. Moreover, the present method is nicely extended to the asymmetric construction of quaternary carbon centers. Some control experiments argue against a radical-based reaction mechanism and a catalytic cycle based on a two-electron process is proposed. Finally, the synthetic utilities of the product are showcased by means of the transformations of the terminal olefin group and the ketone group.

Terminal Trifluoromethylation of Ketones via Selective C-C Cleavage of Cycloalkanols Enabled by Hypervalent Iodine Reagents

We report the first terminal trifluoromethylation at aryl and alkyl ketones' γ, δ, ε, or more remote sites via the selective C-C bond cleavage of cycloalkanols. The noncovalent interactions between alcohols and hypervalent iodines(III) reagents were disclosed to activate both alcohols and the Togni I reagent in the dual photoredox/copper catalysis for the transformation. This reaction was scalable to the gram-scale synthesis, applicable to the structurally complex steroid trifluoromethylation, and extendable to the pentafluoroethylation.

Electrochemical Trifluoromethylation of Thiophenols with Sodium Trifluoromethanesulfinate

We developed an electrochemical trifluoromethylation of thiophenols without the use of metal catalysts and oxidants. This reaction features mild reaction conditions, readily available substrate, as well as moderate to good yields. In addition, this protocol can be easily scaled up with moderate efficiency.

Iron-Catalyzed Ring-Opening Reactions of Cyclopropanols with Alkenes and TBHP: Synthesis of 5-Oxo Peroxides

The ring opening of cyclopropanols is rarely used in multicomponent reactions. Herein we report the three-component reaction of cyclopropanols with alkenes and tert-butyl hydroperoxide (TBHP) catalyzed by an iron catalyst. This protocol enables the incorporation of both the β-carbonyl fragment and a peroxy unit across the C═C double bond regioselectively, thus allowing an efficient, facile access to 5-oxo peroxides. Modification of the biologically active molecules and various downstream derivatizations of the peroxides are also demonstrated.

Radical-Promoted Distal C-H Functionalization of C(sp3 ) Centers with Fluorinated Moieties

Due to their unique properties, fluorinated scaffolds are pivotal compounds in pharmaceuticals, agrochemicals, and materials science. Over the last years, the development of versatile strategies for the selective synthesis of fluorinated molecules by direct C-H bond functionalization has attracted a lot of attention. In particular, the design of novel transformations based on a radical process was a bottleneck for distal C-H functionalization reactions, offering synthetic solutions for the selective introduction of fluorinated groups. This Minireview highlights the major contributions in this blossoming field. The development of new methodologies for the remote functionalization of aliphatic derivatives with various fluorinated groups based on a 1,5-hydrogen atom transfer process and a β-fragmentation reaction will be showcased and discussed.

Nickel-Catalyzed Arylation/Alkenylation of tert-Cyclobutanols with Aryl/Alkenyl Triflates via a CC Bond Cleavage

Herein, we first present a nickel-catalyzed arylation and alkenylation of tert-cyclobutanols with aryl/alkenyl triflates via a C-C bond cleavage. An array of γ-substituted ketones was obtained in moderate-to-good yields, thus featuring earth-abundant nickel catalysis, broad substrate scope, and simple reaction conditions. Preliminary mechanistic experiments indicated that β-carbon elimination pathways might be involved in the catalytic cycle.

Rh(iii)-Catalyzed Csp2–Csp3 bond alkoxylation of α-indolyl alcohols via C–C σ bond cleavage

A Rh(iii)-catalyzed direct Csp²–Csp³ bond alkoxylation of α-(2-indolyl)alcohols with alcohols has been achieved via C–C sigma bond/C–O single bond switch.

Generation of Mixed Anhydrides via Oxidative Fragmentation of Tertiary Cyclopropanols with Phenyliodine(III) Dicarboxylates

Oxidative fragmentation of tertiary cyclopropanols with phenyliodine(III) dicarboxylates in aprotic solvents (dichloromethane, chloroform, toluene) produces mixed anhydrides. The fragmentation reaction is especially facile with phenyliodine(III) reagents bearing electron-withdrawing carboxylate ligands (trifluoroacetyl, 2,4,6-trichlorobenzoyl, 3-nitrobenzoyl), and affords 95−98% yields of the corresponding mixed anhydride products. The latter can be straightforwardly applied for the acylation of various nitrogen, oxygen and sulfur-centered nucleophiles (primary and secondary amines, hydroxylamines, primary alcohols, phenols, thiols). Intramolecular acylation yielding macrocyclic lactones can also be performed. The developed transformation has bolstered the synthetic utility of cyclopropanols as pluripotent intermediates in diversity-oriented synthesis of bioactive natural products and their synthetic congeners. For example, it was successfully applied for the last-stage modification of a cyclic peptide to produce a precursor of a known histone deacetylase inhibitor.

Cu-catalyzed hydroxycyclopropanol ring-opening cyclization to tetrahydrofurans and tetrahydropyrans: short total syntheses of hyperiones

Tetrahydrofurans (THFs) and tetrahydropyrans (THPs) are important core scaffolds frequently found in many molecules of medicinal importance. Herein, we report a novel copper-catalyzed hydroxycyclopropanol ring-opening cyclization methodology to synthesize di- or tri-substituted THFs and THPs. In this reaction, a strained C-C bond was cleaved and a new Csp3-O bond was formed to produce the aforementioned O-heterocycles. The new THF synthesis features a broad substrate scope, scalability, and good functional-group tolerability. It enabled us to complete the shortest enantioselective syntheses of hyperiones A and B (3 and 4 steps, respectively), which is significantly shorter than the previously reported two total syntheses (≥10 steps).

Synthesis of Polysubstituted Pyrroles via Silver-Catalyzed Oxidative Radical Addition of Cyclopropanols to Imines

A silver-catalyzed formal [3 + 2] cycloaddition reaction, with cyclopropanols as a C3 subunit and imines as a two-atom subunit, is developed. The reaction takes place under mild conditions and produces a broad array of polysubstituted pyrroles in medium to high yields. It represents the first example of oxidative radical addition to imines, thus offering a new choice for the direct C-H functionalization of imines.

A silver-catalyzed radical ring-opening reaction of cyclopropanols with sulfonyl oxime ethers

A silver-catalyzed ring-opening reaction of cyclopropanols with sulfonyl oxime ethers has been developed. The protocol was conducted under mild reaction conditions to provide a series of γ-keto oxime ethers with moderate to good yields. The reaction proceeded in a stereoselective manner for CF3-containing oxime ethers to provide a single stereoisomer, while an inseparable E and Z mixture was obtained for CN-containing oxime ethers. Mechanistic studies indicate that the reaction proceeded via a radical mechanism.

A lanthanide ion-doped Ba3Sc2F12 phosphor: hydrothermal synthesis, morphological control, energy transfer, and temperature-sensing performance

Ba₃Sc₂F₁₂ crystals were synthesized by a facile one-step hydrothermal method with Ba/Sc raw material in a ratio of 3 : 2. With the F/Sc ratio increasing from 4 to 8, the obtained crystal's morphology evolved gradually from a strip to a chocolate shape; further, the use of the additives, such as CTAB and EDTA, the obtained crystal's morphology changed from strip to cubic. The energy transfer of Ce³⁺→ Tb³⁺ in the Ba₃Sc₂F₁₂ host was also explored, and it was found to belong to a dipole-dipole interaction mechanism; the color of the light could be adjusted from blue-violet to green due to the different energy transfer efficiencies at different Ce³⁺ and Tb³⁺ ion-doping concentrations. Because of the thermal coupling level of Er³⁺ (²H_11/2→⁴I_15/2 and ⁴S_3/2→⁴I_15/2), Ba₃Sc₂F₁₂:14%Yb³⁺,2%Er³⁺ phosphors showed an excellent temperature-sensing ability with S_A(max) = 0.0043 K^-1 and T_max = 523 K, which are much better than the previously reported values for Yb³⁺/Er³⁺ co-doped systems. The as-prepared lanthanide ion-doped phosphors might have potential to serve as color light/displays and temperature control/sensors.

Cu-Catalyzed Generation of Alkyl Radicals from Alkylsilyl Peroxides and Subsequent C(sp3)-C(sp2) Cross-Coupling with Arylboronic Acids

This work describes a novel and practical method for the Cu-catalyzed C(sp³)-C(sp²) cross-coupling of alkylsilyl peroxides with arylboronic acids. The reductive cleavage of the O-O bond of alkylsilyl peroxides and the desired cross-coupling reactions to afford alkyl-substituted aromatic rings proceed smoothly at room temperature promoted by simple Cu-based catalysts and do not require activation by visible light. The results of mechanistic investigations support a radical-mediated C(sp³)-C(sp²) bond formation via β-scission of the alkoxy radicals generated from the alkylsilyl peroxides.

Divergent Access to Histone Deacetylase Inhibitory Cyclopeptides via a Late-Stage Cyclopropane Ring Cleavage Strategy. Short Synthesis of Chlamydocin

A unified step-economical strategy for accessing histone deacetylase inhibitory peptides is proposed, based on the late-stage installation of multiple zinc-binding functionalities via the cleavage of the strained cyclopropane ring in the common pluripotent cyclopropanol precursor. The efficacy of the proposed diversity-oriented approach has been validated by short stereoselective synthesis of natural product chlamydocin, containing a challenging-to-install fragment of (2S,9S)-2-amino-8-oxo-9,10-epoxydecanoic acid (Aoe) and a range of its analogues, derivatives of 2-amino-8-oxodecanoic and 2-aminosuberic acids.