Copper-Catalyzed Highly Enantioselective Difluoroalkylation of Secondary Propargyl Sulfonates with Difluoroenoxysilanes

Copper-Catalyzed Remote Asymmetric Yne-Allylic Substitution of Yne-Allylic Esters with Anthrones

Anthrones are key structural motifs in many natural products and pharmaceutical chemicals. However, due to its unique tricyclic aromatic structure, the synthetic space for the development of chiral anthrone derivatives is largely limited. By utilizing the potential of the copper-catalyzed remote asymmetric yne-allylic substitution reaction, we describe the first example of copper-catalyzed highly regio- and enantioselective remote yne-allylic substitution on various yne-allylic esters with anthrones under a mild reaction condition, which afforded a range of enantioenriched 1,3-enynes with exhibiting broad functional group tolerance across 51 examples.

Radical Decarboxylation-Initiated SH2' Reaction of β,β-Difluoroenol Sulfonates: Access to α,α-Difluoroketones

Reported herein is a novel radical decarboxylation-initiated SH2' reaction of β,β-difluoroenol sulfonates. This transformation is characterized by mild reaction conditions, a broad substrate scope, and late-stage modification of drug molecules, providing general and mechanistically distinct access to bioactive and synthetically versatile α,α-difluoroketones. Preliminary mechanistic studies demonstrate that this reaction proceeds through a succession of silver-mediated decarboxylative radical generation and radical-addition-induced β-elimination of the sulfonyl radical.

Asymmetric copper-catalyzed alkynylallylic monofluoroalkylations with fluorinated malonates

The unprecedented copper-catalyzed asymmetric alkynylallylic monofluoroalkylation reaction is described via the use of 1,3-enynes and fluorinated malonates. A series of 1,4-enynes bearing a monofluoroalkyl unit are achieved in high yields, excellent regio- and enantioselectivity and high E/Z selectivity. The asymmetric propargylic monofluoroalkylation is also developed. The reliability and synthetic value of the work are highlighted by a gram-scale test and a couple of downstream transformations. Preliminary mechanistic studies unveil a negative nonlinear effect for the catalytic process.

Catalytic Asymmetric Difluoroalkylation Using In Situ Generated Difluoroenol Species as the Privileged Synthon

A robust and practical difluoroalkylation synthon, α,α-difluoroenol species, which generated in situ from trifluoromethyl diazo compounds and water in the presence of dirhodium complex, is disclosed. As compared to the presynthesized difluoroenoxysilane and in situ formed difluoroenolate under basic conditions, this difluoroenol intermediate displayed versatile reactivity, resulting in dramatically improved enantioselectivity under mild conditions. As demonstrated in catalytic asymmetric aldol reaction and Mannich reactions with ketones or imines in the presence of chiral organocatalysts, quinine-derived urea, and chiral phosphoric acid (CPA), respectively, this relay catalysis strategy provides an effective platform for applying asymmetric fluorination chemistry. Moreover, this method features a novel 1,2-difunctionalization process via installation of a carbonyl motif and an alkyl group on two vicinal carbons, which is a complementary protocol to the metal carbene gem-difunctionalization reaction.

Highly Diastereoselective [3 + 2] Cycloaddition of Aziridines with Difluorinated Silyl Enol Ethers: Divergent Synthesis of 4,4-Difluoropyrrolidines and 4-Fluoropyrroles

A highly diastereoselective [3 + 2] cycloaddition of aziridines with difluorinated silyl enol ethers has been developed. This approach provides a facile methodology for highly functionalized gem-difluorinated pyrrolidines in good to excellent yields with good functional group tolerance. A one-pot, two-step approach for synthesis of structurally interesting fluorinated pyrroles has also been developed through a cycloaddition/aromatization/desulfonation sequence. Moreover, readily available substrates, mild reaction conditions, and easy scale-up synthesis show practical advantages.

Copper-Catalyzed Remote Enantioselective Sulfonylation of Yne-Allylic Esters with Sodium Sulfinates

Impressive progress has been made in the copper-catalyzed asymmetric propargylic substitution (APS) reaction, but its use in remote asymmetric yne-allylic substitution remains a challenging topic. Herein, we report the first remote enantioselective copper-catalyzed sulfonylation of yne-allylic esters with sodium sulfinates. The reaction is assumed to occur via a copper-vinylvinylidene species as the key reactive intermediate. The use of readily available starting materials, the mild reaction conditions, and the excellent regio-, enantio- and stereoselectivity, as well as broad substrate scope (>70 examples), show the practicality and attractiveness of this method.

Copper-Catalyzed Regio- and Enantioselective Hydroboration of Difluoroalkyl-Substituted Internal Alkenes

Catalytic asymmetric hydroboration of fluoroalkyl-substituted alkenes is a straightforward approach to access chiral small molecules possessing both fluorine and boron atoms. However, enantioselective hydroboration of fluoroalkyl-substituted alkenes without fluorine elimination has been a long-standing challenge in this field. Herein, a copper-catalyzed hydroboration of difluoroalkyl-substituted internal alkenes with high levels of regio- and enantioselectivities is reported. The native carbonyl directing group, copper hydride system, and bisphosphine ligand play crucial roles in suppressing the undesired fluoride elimination. This atom-economic protocol provides a practical synthetic platform to obtain a wide scope of enantioenriched secondary boronates bearing the difluoromethylene moieties under mild conditions. Synthetic applications including functionalization of biorelevant molecules, versatile functional group interconversions, and preparation of difluoroalkylated Terfenadine derivative are also demonstrated.

Asymmetric Substitution by Alkynyl Copper Driven Dearomatization and Rearomatization

Catalytic asymmetric transformations by dearomatization have developed into a widely applicable synthetic strategy, but heavily relied on the use of arenes bearing a heteroatom. In this case, the dearomatization is facilitated by the involvement of a p-orbital electron of the heteroatom. Different from the conventional substrate-dependent model, here we demonstrate that the activation by a d-orbital electron of the transition-metal center can serve as a driving force for dearomatization, and is applied to the development of a novel asymmetric alkynyl copper facilitated remote substitution reaction. A newly modified PyBox chiral ligand enables the construction of valuable diarylmethyl and triarylmethyl skeletons in high enantioselectivities. An unexpected tandem process involving sequential remote substitution/cyclization/1,5-H shift leads to the formation of the enantioenriched C-N axis. A gram-scale reaction and various downstream transformations highlight the robustness of this method and the potential transformations of the products. Preliminary mechanistic studies reveal a mononuclear Cu-catalyzed remote substitution process.

The Revival of Enantioselective Perfluoroalkylation - Update of New Synthetic Approaches from 2015-2022

Over the last years, methods devoted to the synthesis of asymmetric molecules bearing a perfluoroalkylated chain have been limited in number. Among them, only a few can be used on a large variety of scaffolds. This microreview aims at summarizing these recent advances in enantioselective perfluoroalkylation (-CF3 , -CF2 H, -Cn F2n+1 ) and highlights the need for new enantioselective methods to easily synthesize chiral fluorinated molecules which would be useful for the pharmaceutical and agrochemical industries. Some perspectives are also mentioned.

Chiral gem-difluoroalkyl reagents: gem-difluoroalkyl propargylic borons and gem-difluoroalkyl α-allenols

Chiral fluorinated reagents provide new opportunities for the discovery of drugs and functional materials because the introduction of a fluorinated group significantly alters a molecule's physicochemical properties. Chiral gem-difluoroalkyl fragments (R-CF2-C*) are key motifs in many drugs. However, the scarcity of synthetic methods and types of chiral gem-difluoroalkyl reagents limits the applications of these compounds. Herein, we report two types of chiral gem-difluoroalkyl reagents chiral gem-difluoroalkyl propargylic borons and gem-difluoroalkyl α-allenols and their synthesis by means of methods involving rhodium-catalyzed enantioselective B-H bond insertion reactions of carbenes and Lewis acid-promoted allenylation reactions. The mild, operationally simple method features a broad substrate scope and good functional group tolerance. These two types of reagents contain easily transformable boron and alkynyl or allenyl moieties and thus might facilitate rapid modular construction of chiral molecules containing chiral gem-difluoroalkyl fragments and might provide new opportunities for the discovery of chiral gem-difluoroalkyl drugs and other functional molecules.

Cu/Ag-Mediated One-Pot Enantioselective Synthesis of Fully Decorated 1,2,3-Triazolo[1,5-a]pyrazines

The synthesis of chiral triazole-fused pyrazine scaffolds from readily available substrates in a step-economical asymmetric catalytic way is highly appealing. We herein report that an efficient Cu/Ag relay catalyzed protocol employing cascade asymmetric propargylic amination, hydroazidation, and [3 + 2] cycloaddition reaction with high efficiency to access the target enantioenriched 1,2,3-triazolo[1,5-a]pyrazine has been accomplished by applying a novel N,N,P-ligand. The one-pot reaction of three components exhibits high functional group tolerance, excellent enantioselectivities, and a broad substrate scope with readily available starting materials.

Iron-Catalyzed Alkoxyl Radical-Induced C-C Bond Cleavage/gem-Difluoroalkylation Cascade

An inexpensive iron-catalyzed alkoxyl radical-induced C-C bond cleavage/gem-difluoroalkylation cascade is presented. Regulated by the structure of alkoxyl radical precursors, fluorinated distal diketones were synthesized through a ring-opening strategy and difluoroalkylated medium-sized lactones and macrolactones were constructed via a ring-expansion strategy. Both protocols proceeded under mild and redox neutral conditions with a broad substrate scope and good functional group compatibility.

Palladium-catalyzed highly selective gem-difluoroallylation of propargyl sulfonates with gem-difluoroallylboron

A palladium-catalyzed gem-difluoroallylation of propargyl sulfonates with gem-difluoroallylboron has been developed. The reaction features synthetic simplicity and high functional group tolerance, affording 3,3-difluoro-skipped 1,5-enynes with high efficiency and regioselectivity. In particular, the resulting products can serve as versatile synthons for diversified transformations, having potential applications in medicinal chemistry.

A highly efficient metal-free selective 1,4-addition of difluoroenoxysilanes to chromones

A highly efficient metal-free selective 1,4-addition reaction of difluoroenoxysilanes to chromones was developed using the low-cost and readily available HOTf as the catalyst, which is a facile and straightforward method to access valuable C2-difluoroalkylated chroman-4-one derivatives. Interestingly, the products could be readily converted to the difluorinated bioisostere of the natural product (S)-2,6-dimethylchroman-4-one and a difluorinated benzo-seven-membered heterocycle via the Schmidt rearrangement reaction. In addition, the in vitro anti-proliferative activities of these synthesized derivatives against human colon carcinoma cells (HCT116) revealed that compound 3g exhibited potent inhibitory effect on HCT116 cancer cells with an IC₅₀ value of 6.37 μM, representing a novel lead compound for further structural optimization and biological evaluation.

A Cu-BOX catalysed enantioselective Mukaiyama-aldol reaction with difluorinated silyl enol ethers and acylpyridine N-oxides

A Cu(II)/BOX complex catalyses the enantioselective addition of difluorinated silyl enol ethers to acylpyridine N-oxides. The reaction provides difluorinated chiral tertiary alcohols of great interest in medicinal chemistry. These compounds are obtained in moderate to excellent yields and with high enantioselectivities. The stereochemical outcome of the reaction has been explained by DFT calculations.

Effect of Propargylic Substituents on Enantioselectivity and Reactivity in Ruthenium-Catalyzed Propargylic Substitution Reactions: A DFT Study

We recently proposed a transition-state model for asymmetric propargylic substitution reactions of propargylic alcohols catalyzed by optically active thiolate-bridged diruthenium complexes [Chem. - Asian J.2021, 16, 3760-3766]. In the present study, we further examined the effects of propargylic substituents on both enantioselectivity and reactivity in the propargylic substitution reactions via ωB97X-D-level density functional theory (DFT) calculations. When the propargylic alcohol bears a methyl group at the propargylic position, we obtained results that contrast with the result of our previous study on propargylic alcohols without methyl groups. This result indicates that methyl group substitution at the propargylic position reverses the stereoselectivity. Substitution of a trifluoromethyl group for a methyl group was suggested to result in higher enantioselectivity. The obtained results are consistent with the experimental study on enantioselective propargylic phosphinylation reactions reported by our group.

Catalytic Asymmetric Vinylogous and Bisvinylogous Propargylic Substitution

Distinct regio- and enantioselectivity control in copper-catalyzed vinylogous and bisvinylogous propargylic substitution has been accomplished by using a novel chiral N,N,P ligand. The developed method provides an efficient and selective approach to an array of highly enantioenriched alkynyl unsaturated carbonyl compounds. Salient features include excellent functional group tolerance and broad substrate scope. The synthetic utility of the developed method is further demonstrated by a gram-scale synthesis and by application to a range of transformations including enantioselective synthesis of unique challenging compounds.

Radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters enabled by a carbon shift from an all-carbon quaternary center

Herein, we report an intermolecular, radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters to achieve the goal of building molecular complexity via the one-pot multifunctionalization of alkenes. This reaction allows the expansion of the carbon ring by a carbon shift from an all-carbon quaternary center, and enables further C–C bond formation on the tertiary carbon intermediate with the aim of reconstructing a new all-carbon quaternary center. The good functional group compatibility ensures diverse synthetic transformations of this method. Experimental and theoretical studies reveal that the excellent diastereoselectivity should be attributed to the hydrogen bonding between the substrates and solvent.

Herein, we report an intermolecular, radical 1,2,3-tricarbofunctionalization of α-vinyl-β-ketoesters to achieve the goal of building molecular complexity via the one-pot multifunctionalization of alkenes.

Enantio-, Diastereo- and Regioselective Synthesis of Chiral Cyclic and Acyclic gem-Difluoromethylenes by Palladium-Catalyzed [4+2] Cycloaddition

gem-Difluoromethylene moieties are attractive in medicinal chemistry due to their ability to mimic other more ubiquitous functional groups. Thus, effective asymmetric methods for their construction are highly desirable, especially for the industrial production of chiral drugs. Using a Pd-catalyzed asymmetric [4+2] cycloaddition between substituted-2-alkylidenetrimethylene carbonates and gem-difluoroalkyl ketones, we were able to easily access chiral 1,3-dioxanes that contain a tetrasubstituted difluoroalkyl stereogenic center in cyclic and acyclic skeletons. A novel phosphoramidite ligand, which contains a bulky 1,1-dinaphthylmethanamino moiety, was developed to provide the products in high yield with excellent enantio-, diastereo-, and regioselectivity. Strikingly, the gem-difluoro substitution pattern promotes the reaction, and pentafluoroethylketone, an α,α-difluorinated β-ketoester, and a β-ketosulfone are suitable substrates for this method.

Visible-Light-Induced para-Difluoroalkylation of Aniline Derivatives

Visible-light-induced, iridium catalyzed, para-selective C-H difluoroalkylation of aniline derivatives under mild reaction conditions is reported. Various substrates and bioactive compounds, such as precursors of vorinostat and chlorpropham, were all well tolerated. This protocol features a wide substrate scope, high regioselectivity, low catalyst usage, and operational simplicity.

Direct benzylic C–H difluoroalkylation with difluoroenoxysilanes by transition metal-free photoredox catalysis

A visible light promoted direct benzylic C–H difluoroalkylation with difluoroenoxysilanes catalyzed by Na2-eosin Y via a HAT-ORPC pathway has been developed, providing an efficient and atom-economic method for production of α-benzyl-α,α-difluoroketones.

Stereoselective synthesis of C3-tetrasubstituted oxindoles via copper catalyzed asymmetric propargylation

Herein, a copper catalyzed asymmetric propargylation of 2-oxindole-3-carboxylate esters with terminal propargylic esters is described. This strategy successfully provides a direct approach to constructing a broad range of chiral C3-tetrasubstituted oxindoles with contiguous tertiary and quaternary carbon stereocenters in high yields and excellent enantioselectivities (16 examples, up to 99% yield and 98% ee). Moreover, the diastereoisomers of the two newly formed stereocenters can be separated by silica gel chromatography, thereby providing a valuable stereoselective access to all four possible stereoisomers of C3-tetrasubstituted oxindoles.

Herein, a copper catalyzed asymmetric propargylation of 2-oxindole-3-carboxylate esters with terminal propargylic esters is described.

Asymmetric difluorocarbonylation reactions of non-active imines catalyzed by Bi(OAc)3/chiral phosphoric acid

Difluorinated carbonyl has been identified as the basic skeleton of multitudinous biologically active molecules.

Construction of poly-N-heterocyclic scaffolds via the controlled reactivity of Cu-allenylidene intermediates

Controlling the sequence of the three consecutive reactive carbon centres of Cu-allenylidene remains a challenge. One of the impressive achievements in this area is the Cu-catalyzed annulation of 4-ethynyl benzoxazinanones, which are transformed into zwitterionic Cu-stabilized allenylidenes that are trapped by interceptors to provide the annulation products. In principle, the reaction proceeds via a preferential γ-attack, while annulation reactions via an α- or β-attack are infrequent. Herein, we describe a method for controlling the annulation mode, by the manipulation of a CF₃ or CH₃ substituent, to make it proceed via either a γ-attack or an α- or β-attack. The annulation of CF₃-substituted substrates with sulfamate-imines furnished densely functionalized N-heterocycles with excellent enantioselectivity via a cascade of an internal β-attack and an external α-attack. CH₃-variants were transformed into different heterocycles that possess a spiral skeleton, via a cascade of an internal β-attack and a hydride α-migration followed by a Diels-Alder reaction.

Regio- and enantioselective umpolung gem-difluoroallylation of hydrazones via palladium catalysis enabled by N-heterocyclic carbene ligand

The enantioselective construction of C-CF₂R (R: alkyl or fluoroalkyl) bonds has attracted the attention of synthetic chemists because of the importance of chiral fluorinated compounds in life and materials sciences. Catalytic asymmetric fluoroalkylation has mainly been realized under organocatalysis and Lewis acid catalysis, with substrates limited to carbonyl compounds. Few examples using transition-metal catalysis exist, owing to side reactions including decomposition and isomerization of fluoroalkylating reagents. Herein we report umpolung asymmetric difluoroallylation of hydrazones with 3-bromo-3,3-difluoropropene (BDFP) under palladium catalysis. Difluoroallylation products having quaternary chiral carbon centers are afforded in good yields with high α/γ- and enantioselectivities. The usefulness of the reaction products is demonstrated and an inner-sphere mechanism of the reaction is proposed. The use of chiral N-heterocyclic carbene as ligand is the key for the selectivities as well as the productivity of the reaction.

Ruthenium- and Copper-Catalyzed Propargylic Substitution Reactions of Propargylic Alcohol Derivatives with Hydrazones

Ruthenium- and copper-catalyzed propargylic substitution reactions of propargylic alcohol derivatives with N-monosubstituted hydrazones as ambident nucleophiles are achieved in which N-monosubstituted hydrazones exhibit impressive different reactivities depending on different catalytic systems, behaving as carbon-centered nucleophiles to give the corresponding propargylic alkylated products in ruthenium catalysis, or as nitrogen-centered nucleophiles to afford the corresponding propargylic aminated products in copper catalysis. DFT calculations were carried out to investigate the detailed reaction pathways of these two systems. Further transformation of propargylic substituted products affords the corresponding multisubstituted pyrazoles as cyclization products in good to high yields.

Catalyst-free gem-chlorosulfurization of difluoromethyl-substituted diazo compounds with disulfide and PhICl2

A series of gem-chlorosulfurization products bearing difluoromethyl substituents were synthesized in high to excellent yields directly from p-toluenesulfonyl difluorodiazoethane (TsCF₂CHN₂), disulfides and PhICl₂ without any catalysts or additives. The mild reaction conditions and high functional group compatibility indicated the utility and sustainability of the method. In addition, the gem-chlorosulfurization products could be efficiently converted to sulfur-containing and aryl substituted difluoromethyl derivatives by a feasible multi-component operation.

Visible-Light-Induced Palladium-Catalyzed Selective Defluoroarylation of Trifluoromethylarenes with Arylboronic Acids

Selective functionalization of inactive C(sp³)-F bonds to prepare medicinally interesting aryldifluoromethylated compounds remains challenging. One promising route is the transition-metal-catalyzed cross-coupling through oxidative addition of the C(sp³)-F bond in trifluoromethylarenes (ArCF₃), which are ideal precursors for this process due to their ready availability and low cost. Here, we report an unprecedented excited-state palladium catalysis strategy for selective defluoroarylation of trifluoromethylarenes with arylboronic acids. This visible-light-induced palladium-catalyzed cross-coupling proceeds under mild reaction conditions and allows transformation of a variety of arylboronic acids and ArCF₃. Preliminary mechanistic studies reveal that the oxidative addition of the C(sp³)-F bond in ArCF₃ to excited-state palladium(0) via a single electron transfer pathway is responsible for the C(sp³)-F bond activation.

Solvent-Dependent Cyclization of 2-Alkynylanilines and ClCF2COONa for the Divergent Assembly of N-(Quinolin-2-yl)amides and Quinolin-2(1H)-ones

Herein, we present an expedient Cu-catalyzed [5 + 1] cyclization of 2-alkynylanilines and ClCF₂COONa to divergent construction of N-(quinolin-2-yl)amides and quinolin-2(1H)-ones by regulating the reaction solvents. Notably, nitrile acts as a solvent and performs the Ritter reactions. ClCF₂COONa is used as a C1 synthon in this transformation, which also represents the first example for utilization of ClCF₂COONa as an efficient desiliconization reagent. The current protocol involves in situ generation of isocyanide, copper-activated alkyne, Ritter reaction and protonation.

Asymmetric α-electrophilic difluoromethylation of β-keto esters by phase transfer catalysis

An efficient and enantioselective α-electrophilic difluoromethylation of β-keto esters has been achieved by phase-transfer catalysis. This procedure is applicable to different kinds of β-keto esters with a series of cinchona-derived C-2' aryl-substituted phase-transfer catalysts. The reaction gives the corresponding products in good enantioselectivities (up to 83% ee) and yields (up to 92%) with high C/O regioselectivities (up to 98 : 2). Moreover, the C/O selectivity of β-keto esters could be easily reversed and controlled. This asymmetric difluoromethylation provided a novel and efficient way for introducing chiral C-CF2H groups.

Ruthenium-Catalyzed Enantioselective Propargylic Phosphinylation of Propargylic Alcohols with Phosphine Oxides

The development of transition metal-catalyzed enantioselective propargylic substitution reactions has gained much progress in recent years, however, no successful example with phosphorus-centered nucleophiles has yet been reported until now. Herein, we report the first successful example of ruthenium-catalyzed enantioselective propargylic substitution reactions of propargylic alcohols with diarylphosphine oxides as phosphorus-centered nucleophiles. This synthetic approach provides a new method to prepare chiral phosphorus-containing organic compounds.

Palladium-catalyzed defluorinative alkynylation of polyfluoroalkyl ketones with alkynes for the synthesis of fluorinated fused furans

A Pd-catalyzed C–F bond alkynylation of polyfluoroalkyl ketones with terminal alkynes for the synthesis of fluoroalkylated fused furans was developed.

Cu-Catalyzed radical-triggered spirotricyclization of enediynes and enyne-nitriles for the synthesis of pentacyclic spiroindenes

A new copper-catalyzed radical-triggered fluoromethylation-spirotricyclization of enediyne- and enyne-nitrile-containing para-quinone methides (p-QMs) was reported for the first time, and used to produce a series of hitherto unreported pentacyclic spiroindenes.

HFIP-catalyzed direct dehydroxydifluoroalkylation of benzylic and allylic alcohols with difluoroenoxysilanes

Hexafluoroisopropanol (HFIP)-catalyzed direct dehydroxydifluoroalkylation of benzylic and allylic alcohols with difluoroenoxysilanes is developed.

Catalytic AgF-Initiated Intramolecular 1,3-Sulfonyl Migration of gem-Difluorovinyl Sulfonates to α,α-Difluoro-β-ketosulfones

A 1,3-sulfonyl migration of difluorovinyl sulfonates initiated by a catalytic amount of silver fluoride is presented. α,α-Difluoro-β-ketosulfones were successfully prepared in excellent yields. This method features high chemoselectivity, good functional group tolerance, high atom economy, and mild, environmentally benign reaction conditions. Furthermore, mechanistic experiments indicate that this migration proceeds in an intermolecular pathway and the corresponding sulfinates are possible intermediates.