Highly enantioselective copper-catalyzed electrophilic trifluoromethylation of β-ketoesters

The Role of Ate Complexes in the Copper-Mediated Trifluoromethylation of Alkynes

Trifluoromethylation reactions have recently received increased attention because of the beneficial effect of the trifluoromethyl group on the pharmacological properties of numerous substances. A common method to introduce the trifluoromethyl group employs the Ruppert-Prakash reagent, that is, Si(CH3 )3 CF3 , together with a copper(I) halide. We have applied this method to the trifluoromethylation of aromatic alkynes and used electrospray-ionization mass spectrometry to investigate the mechanism of these reactions in tetrahydrofuran, dichloromethane, and acetonitrile as well as with and without added 1,10-phenanthroline. In the absence of the alkyne component, the homoleptic ate complexes [Cu(CF3 )2 ](-) and [Cu(CF3 )4 ](-) were observed. In the presence of the alkynes RH, the heteroleptic complexes [Cu(CF3 )3 R](-) were detected as well. Upon gas-phase fragmentation, these key intermediates released the cross-coupling products R-CF3 with perfect selectivity. Apparently, the [Cu(CF3 )3 R](-) complexes did not originate from homoleptic cuprate anions, but from unobservable neutral precursors. The present results moreover point to the involvement of oxygen as the oxidizing agent.

An Energetic Guide for Estimating Trifluoromethyl Cation Donor Abilities of Electrophilic Trifluoromethylating Reagents: Computations of X-CF3 Bond Heterolytic Dissociation Enthalpies

This work established an energetic guide for estimating the trifluoromethyl cation-donating abilities (TC(+)DA) of electrophilic trifluoromethylating reagents through computing X-CF3 bond (X = O, S, Se, Te, and I) heterolytic dissociation enthalpies. TC(+)DA values for a wide range of popular reagents were derived on the basis of density functional calculations (M06-2X). A good correspondence has been identified between the computed TC(+)DA values and the experimentally observed relative trifluoromethylating capabilities of the reagents. Substituent effects hold good linear free energy relationships on the TC(+)DAs of the most widely used reagents including Umemoto reagent, Yagupolskii-Umemoto reagent, and Togni reagents, which allow their trifluoromethylating capabilities to be rationally tuned by substituents and thus extend their synthetic utility. All the information disclosed in this work would contribute to future rational exploration of the electrophilic trifluoromethylation chemistry.

Advances in Synthetic Applications of Hypervalent Iodine Compounds

The preparation, structure, and chemistry of hypervalent iodine compounds are reviewed with emphasis on their synthetic application. Compounds of iodine possess reactivity similar to that of transition metals, but have the advantage of environmental sustainability and efficient utilization of natural resources. These compounds are widely used in organic synthesis as selective oxidants and environmentally friendly reagents. Synthetic uses of hypervalent iodine reagents in halogenation reactions, various oxidations, rearrangements, aminations, C-C bond-forming reactions, and transition metal-catalyzed reactions are summarized and discussed. Recent discovery of hypervalent catalytic systems and recyclable reagents, and the development of new enantioselective reactions using chiral hypervalent iodine compounds represent a particularly important achievement in the field of hypervalent iodine chemistry. One of the goals of this Review is to attract the attention of the scientific community as to the benefits of using hypervalent iodine compounds as an environmentally sustainable alternative to heavy metals.

Iron-catalyzed trifluoromethylation of vinylcyclopropanes: facile synthesis of CF3–containing dihydronaphthalene derivatives

FeCl₂-catalyzed trifluoromethylation of vinylcyclopropanes to generate a series of CF₃-containing dihydronaphthalene derivatives in moderate to high yields (up to 96%) under mild reaction conditions was successfully developed.

Electrophilic trifluoromethylation of carbonyl compounds and their nitrogen derivatives under copper catalysis

Recent advances in copper-catalyzed electrophilic trifluoromethylation of carbonyl compounds and their nitrogen derivatives are highlighted with particular focus on C–CF₃ bond forming reactions.

An efficient approach for the construction of trifluoromethylated all-carbon quaternary stereocenters: enantioselective Ni(ii)-catalyzed Michael addition of 2-acetyl azaarene to β,β-disubstituted nitroalkenes

Michael addition of 2-acetyl azaarenes with β,β-disubstituted nitroalkenes afforded chiral compounds in good yields and with excellent enantioselectivities.

Recent advances in trifluoromethylation of organic compounds using Umemoto's reagents

The incorporation of fluorine-containing moieties into organic compounds is of great importance in pharmaceutical, agricultural, and materials science. Within these organofluorides, the trifluoromethyl group is one of the most important motifs. In recent years, the trifluoromethyl group has attracted more and more attention, and many trifluoromethylated compounds have been found to possess special activities. However, until now, only a few methods have been developed to achieve this efficiently using Umemoto's reagents. This review highlights recent developments in the direct introduction of a trifluoromethyl group into organic compounds with Umemoto's reagents. Seven approaches to the trifluoromethylation of organic compounds are summarized: (i) trifluoromethylation of arenes, (ii) trifluoromethylation of alkenes, (iii) trifluoromethylation of terminal alkynes, (iv) deoxygenative trifluoromethylation of benzylic xanthates, (v) trifluoromethylation of ketoesters, (vi) trifluoromethylation of aryl boronic acids and aromatic amines (synthesis of ArCF3) and (vii) trifluoromethylation of biphenyl isocyanide derivatives.

Photo-organocatalytic Enantioselective Perfluoroalkylation of β-Ketoesters

The visible-light-driven, phase-transfer-catalyzed, enantioselective perfluoroalkylation and trifluoromethylation of cyclic β-ketoesters is described. The photo-organocatalytic process, which occurs at ambient temperature and under visible light illumination, is triggered by the photochemical activity of in situ-generated electron donor-acceptor complexes, arising from the association of chiral enolates and perfluoroalkyl iodides. Preliminary mechanistic studies are reported.

Towards an asymmetric organocatalytic α-cyanation of β-ketoesters

This communication describes the first proof of concept for an asymmetric α-cyanation of β-ketoesters using a hypervalent iodine-based electrophilic cyanide-transfer reagent. A series of different organocatalysts has been investigated and it was found that the use of naturally occurring Cinchona alkaloids allows obtaining the target products in good yields and with moderate enantioselectivities up to er = 76:24 under operationally simple conditions.

Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate

Catalytic trifluoromethylation of aryl- and vinylboronic acids by 2-cyclopropyl-1-(trifluoromethyl)benzo[b]thiophenium triflate is described. In the presence of a catalytic amount of CuOAc and 2,4,6-collidine in ethyl acetate, the reaction proceeded in good to high yields for various substrates under mild reaction conditions at room temperature.

Metal-free radical perfluoroalkylation of (hetero)arenes

We report a metal-free radical perfluoroalkylation method which uses inexpensive and commercially available perfluorocarboxylic anhydrides as an easy to use source of perfluoroalkyl radicals.

Anionic chiral tridentate N-donor pincer ligands in asymmetric catalysis

Tridentate monoanionic ligands known as "pincers" have gained a prominent place as ligands for transition metals and, more recently, for main-group metals and lanthanides. They have been widely employed as ancillary ligands for metal complexes studied inter alia in bond activation steps relevant to catalytic processes. The central formally anionic aryl or heteroaryl unit acts as an "anchor" in the coordination to the metal, which kinetically stabilizes the resulting complexes. Their stability, activity, and reactivity can be tuned by subtle modifications of substitution patterns on the pincer ligand or by modifying the donor atoms. The challenges in pincer ligand design for enantioselective catalysis have been met by their assembly from rigid heterocycles and chiral ligating units in the "wingtip" positions, which generally contain the stereochemical information. The resulting well-defined geometry and shape of the reactive sector of the molecular catalyst favor orientational control of the substrates. On the other hand, the kinetic stability allows reduced catalyst loadings. Recently, a new generation of tridentate anionic N(∧)N(∧)N pincer ligands has been developed which give rise to highly enantioselective transformations. Their applications in asymmetric catalysis have focused primarily on the asymmetric Nozaki-Hiyama-Kishi coupling of aldehydes with halogenated hydrocarbons as well as Lewis acid catalysis involving enantioselective electrophilic attack onto metal-activated β-keto esters, oxindoles, and related substrates. These include highly selective protocols for Friedel-Crafts alkylations with Michael acceptors, electrophilic fluorinations, trifluoromethylations, azidations, and alkylations and subsequent transformations. Increasingly, these stereodirecting ligands are being employed in other types of transformations, including hydrosilylations, cyclopropanations, and epoxidations. The stability and well-defined nature of the molecular catalysts have made them attractive targets for mechanistic studies into a wide range of these transformations, thus providing the type of insight required for a more rational approach to catalyst development. This Account reviews work performed by us and other groups in the field and places it into perspective in relation to general research efforts in enantioselective catalysis.

Copper-catalyzed synthesis of α-trifluoromethylthio-substituted ketones

The CF3S-substituted moiety serves as an important structural element in many bioactive molecules. A versatile copper catalyst that allowed for trifluoromethylthiolation of primary and secondary α-bromoketones is described. The reaction with readily available elemental sulfur and CF3SiMe3 afforded a broad scope and moderate to good yields of α-trifluoromethylthio-substituted ketones. This procedure represents a very operationally simple yet powerful strategy for the synthesis of α-trifluoromethylthio-substituted ketones, a useful and versatile class of synthetic synthons.

Structural reevaluation of the electrophilic hypervalent iodine reagent for trifluoromethylthiolation supported by the crystalline sponge method for X-ray analysis

Hypervalent iodine λ3-benziodoxoles are common electrophilic transfer reagents known for their enhanced stability compared to their non-cyclic analogues. Herein we present data showing that chlorobenziodoxole reacts with two different thiolate nucleophiles (thiocyanate and trifluoromethylthiolate), resulting in the formation of stable thioperoxy complexes rather than the expected benziodoxole derivatives. We further report a revised structure for the earlier described electrophilic trifluoromethylthiolation reagent (1), which was previously believed to contain the benziodoxole framework. Our findings, which are based on a combination of analytical techniques, including the recently introduced crystalline sponge method for X-ray analysis, unambiguously demonstrate that 1 is a thioperoxy compound both in solution and the solid state.

Catalytic C-H α-trifluoromethylation of α,β-unsaturated carbonyl compounds

A copper(I)-catalyzed, regioselective C-H α-trifluoromethylation of α,β-unsaturated carbonyl compounds using Togni's reagent was developed. Diverse substrates, including enones as well as α,β-unsaturated esters, thioesters, and amides, stereospecifically afforded the corresponding (E)-α-trifluoromethylated products in moderate to high yields. Further, this method was applied to the C-H trifluoromethylation of drugs.