Recent advances in stereoselective construction of fluorinated quaternary carbon centers from fluorinated compounds

There are many fluorinated quaternary carbon structural units in pharmaceuticals and bioactive compounds. Organic chemists are interested in the stereoselective synthesis of fluorinated quaternary carbon structural units. Constructing a fluorinated quaternary carbon stereocenter can be achieved directly and efficiently by the asymmetric catalytic reaction of fluorinated compounds as substrates. This approach aims to construct fluorinated quaternary carbon stereocenters while diversifying the types of fluorinated compounds. This review introduces a series of reactions for synthesizing fluorinated quaternary carbon chiral centers through asymmetric organic catalysis and transition metal catalysis, including alkylation, arylation, Mannich, Michael addition, and allylation reactions. This work will contribute to the development of the synthesis of fluorinated quaternary carbon chiral center-containing compounds in the future.

2-Oxindole and related heterocycles: synthetic methodologies for their natural products and related derivatives

Natural goods, medications, and pharmaceutically active substances all contain substituted oxindoles. Generally, the C-3 stereocenter of the substituents of oxindoles and their absolute arrangement have a substantial impact on the bioactivity of these substances. In this case, the desire for contemporary probe and drug-discovery programs for the synthesis of chiral compounds using desirable scaffolds with high structural diversity further drives research in this field. Also, the new synthetic techniques are generally simple to apply for the synthesis of other similar scaffolds. Herein, we review the distinct approaches for the synthesis of diverse useful oxindole scaffolds. Specifically, the research findings on the naturally existing 2-oxindole core and a variety of synthetic compounds having a 2-oxindole core are discussed. We present an overview of the construction of oxindole-based synthetic and natural products. In addition, the chemical reactivity of 2-oxindole and its related derivatives in the presence of chiral and achiral catalysts are thoroughly discussed. The data compiled herein provides broad information related to the bioactive product design, development, and applications of 2-oxindoles and the reported techniques will be helpful for the investigation of novel reactions in the future.

Electrochemical monofluoroalkylation cyclization of N-arylacrylamides to construct monofluorinated 2-oxindoles

An electrochemical monofluoroalkylation cyclization of N-arylacrylamides to synthesize monofluorinated 2-oxindoles has been developed, which employs common dimethyl 2-fluoromalonate as a monofluoroalkyl radical precursor and obviates the use of prefunctionalized monofluoroalkylation reagents and sacrificial oxidants. A variety of monofluorinated nitrogen-containing heterocyclic compounds were efficiently obtained with satisfactory yields from readily available materials.

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.

Enantioselective Synthesis of Acyclic Stereotriads Featuring Fluorinated Tetrasubstituted Stereocenters

Elaboration of enantioenriched complex acyclic stereotriads represents a challenge for modern synthesis even more when fluorinated tetrasubstituted stereocenters are targeted. We have been able to develop a simple strategy in a sequence of two unprecedented steps combining a diastereoselective aldol-Tishchenko reaction and an enantioselective organocatalyzed kinetic resolution. The aldol-Tishchenko reaction directly generates a large panel of acyclic 1,3-diols possessing a fluorinated tetrasubstituted stereocenter by condensation of fluorinated ketones with aldehydes under very mild basic conditions. The anti 1,3-diols featuring three contiguous stereogenic centers are generated with excellent diastereocontrol (typically >99 : 1 dr). Depending upon the precursors both diastereomers of stereotriads are accessible through this flexible reaction. Furthermore, from the obtained racemic scaffolds, development of an organocatalyzed kinetic resolution enabled to generate the desired enantioenriched stereotriads with excellent selectivity (typically er >95 : 5).

Recent advances in cyclization reactions of isatins or thioisatins via C–N or C–S bond cleavage

This review summarizes recent developments on cyclization reactions induced by the C–N or C–S bond cleavage of isatins or thioisatins in the last 5 years, which produce fused products instead of spiro compounds.

Regioselective Markovnikov hydrodifluoroalkylation of alkenes using difluoroenoxysilanes

Alkene hydrodifluoroalkylation is a fruitful strategy for synthesizing difluoromethylated compounds that are interesting for developing new medicinal agents, agrochemicals, and advanced materials. Whereas the anti-Markovnikov hydrodifluoroalkylation to linear-type products is developed, employing radical-based processes, the Markovnikov synthesis of branched adducts remains unexplored. Herein, we describe acid-catalyzed processes involving carbocation intermediates as a promising strategy to secure the Markovnikov regioselectivity. Accordingly, the Markovnikov hydrodifluoroalkylation of mono-, di-, tri-, and tetrasubstituted alkenes using difluoroenoxysilanes, catalyzed by Mg(ClO4)2·6H2O, is achieved. This allows the diversity-oriented synthesis of α,α-difluoroketones with a quaternary or tertiary carbon at the β-position that are otherwise difficult to access. The method is applied to the modification of natural products and drug derivatives. The resulting α,α-difluorinated ketones could be converted to the corresponding α,α-difluorinated esters or alcohols, or organofluorine compounds featuring a CF2H or CF2CF2Ph moiety. Mechanistic studies support that Mg(ClO4)2·6H2O functions as a hidden Brønsted acid catalyst.

Copper-catalyzed enantioselective Mukaiyama aldol reaction of silyl enol ethers with isatins

A highly enantioselective Mukaiyama aldol reaction of silyl enol ethers with isatins catalyzed by chiral copper complexes was developed. A series of chiral 3-substituted 3-hydroxy-2-oxindoles bearing a tetra-substituted center could be obtained exclusively with high yields (up to 95%) and excellent enantioselectivities (up to 99%). In particular, water was essential to improve the diastereoselectivity.

HClO4 catalysed aldol-type reaction of fluorinated silyl enol ethers with acetals or ketals toward fluoroalkyl ethers

A highly efficient metal-free catalytic aldol-type reaction of fluorinated enol silyl ethers and acetals/ketals toward functionalized fluoroalkyl ethers is developed by using less than 1.0 mol% HClO₄ (70 wt%, aq.).

A Sc(OTf)3 catalyzed Mukaiyama–Mannich reaction of difluoroenoxysilanes with unactivated ketimines

The first example of a Mukaiyama–Mannich reaction of difluoroenoxysilanes with unactivated ketimines catalyzed by Sc(OTf)₃ is described.

Organocatalytic asymmetric Michael addition between 3-subsituted oxindoles and enals catalyzed by camphor sulfonyl hydrazine

3,3-Disubstituted oxindoles containing vicinal stereogenic carbon centers have been synthesized through organocatalytic asymmetric Michael addition between 3-substituted oxindoles and enals catalyzed by chiral camphor sulfonyl hydrazines (CaSHs).

Catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers

This feature article highlights our recent achievements in catalytic selective mono- and difluoroalkylation using fluorinated silyl enol ethers (FSEEs).

Development of Synthetic Methodologies via Catalytic Enantioselective Synthesis of 3,3-Disubstituted Oxindoles

3,3-Disubstituted oxindoles are widely distributed in natural products, drugs, and pharmaceutically active compounds. The absolute configuration and the substituents on the fully substituted C3 stereocenter of the oxindole often significantly influence the biological activity. Therefore, tremendous efforts have made to develop catalytic enantioselective syntheses of this prominent structural motif. Research in this area is further fueled by the ever-increasing demand for modern probe- and drug-discovery programs for synthetic libraries of chiral compounds that are derived from privileged scaffolds with high structural diversity. Notably, the efficient construction of fully substituted C3 stereocenters of oxindole, tetrasubstituted or all-carbon quaternary, spirocyclic or not, also becomes a test ground for new synthetic methodologies. We have been engaged in developing efficient methods for diversity-oriented synthesis of chiral 3,3-disubstituted oxindoles from readily available starting materials. We have systematically developed catalytic enantioselective methods to prepare 3-substituted 3-hydroxyoxindoles, 3-aminooxindoles, and 3-thiooxindoles, quaternary oxindoles, and spirocyclic oxindoles. These protocols can be classified into six approaches: (1) enantioselective addition of nucleophiles to isatins or isatin ketimines; (2) unprotected 3-substituted oxindoles as nucleophiles; (3) functionalization of oxindole-derived tetrasubstituted alkenes; (4) desymmetrization of oxindole-based diynes; (5) spirocyclopropyl oxindoles as donor-acceptor (D-A) cyclopropanes; and (6) elaboration of diazooxindoles. By the use of these methods, chiral oxindoles with rich structural diversity are readily accessed with high to excellent enantioselectivity. Some methods have been used for the enantioselective formal or total synthesis of natural products, bioactive compounds, or their analogues. On the basis of these studies, we developed synthetic methodologies that have potential application. We designed phosphoramide-based bifunctional catalysts for the efficient construction of quaternary oxindoles: a cinchona-alkaloid-derived phosphoramide for the Michael addition of unprotected 3-substituted oxindoles to nitroolefins with broad substrate scope and a chiral 1,2-cyclohexanediamine-derived bifunctional phosphoramide for the activation of fluorinated enol silyl ethers for the addition to isatylidene malononitrile. The phosphoramide-based catalysts achieved better enantiofacial control than the analogous H-bond-donor-derived catalysts in these reactions, suggesting the potential of the former in new chiral catalyst development. We identified chiral Au(I) and Hg(II) catalysts for olefin cyclopropanation of diazooxindoles. We further disclosed the effective activation of spirocyclopropyl oxindoles by using electron-withdrawing N-protecting groups for enantioselective [3 + 3] cycloaddition, offering the promise of constructing a diverse range of spirocyclic oxindoles by the use of such monoactivated D-A cyclopropanes. We developed tandem sequences that allow the facile synthesis of 3,3-disubstituted oxindoles from simple starting materials in a one-pot operation, including a tandem Morita-Baylis-Hillman/bromination/[3 + 2] annulation sequence, a hydrogenation/ketimine formation/asymmetric 6π electrocyclization sequence, a C-H functionalization/Michael addition or amination sequence, and an aza-Wittig/Strecker sequence. We designed oxindole-based diynes to realize a highly enantioselective Cu-catalyzed alkyne-azide cycloaddition (CuAAC), outlining the desymmetrization of prochiral diynes as an effective strategy to exploit asymmetric CuAAC. This Account focuses on the synthetic methodologies developed in our group for the catalytic enantioselective synthesis of 3,3-disubstituted oxindoles and provides an overview of our research on the design, development, and applications of these methods that will provide useful insights for the exploration of new reactions.

Modern Approaches for Asymmetric Construction of Carbon-Fluorine Quaternary Stereogenic Centers: Synthetic Challenges and Pharmaceutical Needs

New methods for preparation of tailor-made fluorine-containing compounds are in extremely high demand in nearly every sector of chemical industry. The asymmetric construction of quaternary C-F stereogenic centers is the most synthetically challenging and, consequently, the least developed area of research. As a reflection of this apparent methodological deficit, pharmaceutical drugs featuring C-F stereogenic centers constitute less than 1% of all fluorine-containing medicines currently on the market or in clinical development. Here we provide a comprehensive review of current research activity in this area, including such general directions as asymmetric electrophilic fluorination via organocatalytic and transition-metal catalyzed reactions, asymmetric elaboration of fluorine-containing substrates via alkylations, Mannich, Michael, and aldol additions, cross-coupling reactions, and biocatalytic approaches.

Asymmetric vinylogous Mukaiyama aldol reaction of isatins under bifunctional organocatalysis: enantioselective synthesis of substituted 3-hydroxy-2-oxindoles

A highly enantioselective organocatalytic vinylogous Mukaiyama aldol reaction of silyloxy dienes and isatins under bifunctional organocatalysis is presented.

A triple-functionalised metal centre-catalyzed enantioselective multicomponent reaction

A model of a triple-functionalised metal centre for the discovery of unprecedented enantioselective reactions was exquisitely developed by using a Rh^I/(DHQ)₂PHAL catalyst system via multiple coordination interactions with different ligands and substrates.

A general and efficient Lewis acid catalysed Mukaiyama-aldol reaction of difluoroenoxysilanes and ketones

We report a general and highly efficient Mukaiyama-aldol reaction of ketones and difluoroenoxysilanes. While the reaction of aryl ketones worked efficiently in the presence of Bi(OTf)₃, that of aliphatic ketones required the use of Sc(OTf)₃. In addition, Sc(OTf)₃ was capable of achieving excellent 1,2-selectivity in the corresponding reaction of α,β-unsaturated ketones. This method provides a facile access to differently substituted β-hydroxy α,α-difluoro ketones, versatile synthons for difluomethylated tertiary alcohols.

Catalytic Enantioselective Michael Addition Reactions of Tertiary Enolates Generated by Detrifluoroacetylation

This work describes, for the first time, Michael addition reactions of tertiary fluoro-enolates in situ generated by detrifluoroacetylation with 1-(1-(phenylsulfonyl) vinylsulfonyl)benzene. Excellent enantioselectivity and chemical yields were achieved with application of catalysts (10 mol %) derived from Cu(OTf)₂ and (1S,2S)-1,2-diphenylethane-1,2-diamine. These reactions show a considerable degree of structural generality and allow the preparation of new types of biologically relevant molecules that contain quaternary C-F stereogenic carbon atoms and feature five-, six-, or seven-membered rings as well as heterocyclic 3-fluoro-2,3-dihydrochromen-4-one moieties.

Ni(ii)-Catalyzed enantioselective Mukaiyama–Mannich reaction between silyl enol ethers and cyclic N-sulfonyl α-ketiminoesters

The first Ni(ii)-catalyzed Mukaiyama–Mannich reaction of cyclic N-sulfonyl α-ketiminoesters with silyl enol ethers was realized and provided enantioenriched benzofused sultams containing a quaternary α-amino ester.

Catalytic asymmetric synthesis of biologically important 3-hydroxyoxindoles: an update

Oxindole scaffolds are prevalent in natural products and have been recognized as privileged substructures in new drug discovery. Several oxindole-containing compounds have advanced into clinical trials for the treatment of different diseases. Among these compounds, enantioenriched 3-hydroxyoxindole scaffolds also exist in natural products and have proven to possess promising biological activities. A large number of catalytic asymmetric strategies toward the construction of 3-hydroxyoxindoles based on transition metal catalysis and organocatalysis have been reported in the last decades. Additionally, 3-hydroxyoxindoles as versatile precursors have also been used in the total synthesis of natural products and for constructing structurally novel scaffolds. In this review, we aim to provide an overview about the catalytic asymmetric synthesis of biologically important 3-substituted 3-hydroxyoxindoles and 3-hydroxyoxindole-based further transformations.

Zn/Sc bimetallic relay catalysis: one pot cycloisomerization/carbonyl–ene reaction toward oxazole derivatives

A novel tandem metal relay catalytic system combining Zn(ii)-catalyzed cycloisomerization and a Sc(iii)-catalyzed carbonyl–ene reaction has been successfully developed.

Organocatalytic enantioselective Mukaiyama–Mannich reaction of fluorinated enol silyl ethers and cyclic N-sulfonyl ketimines

The first catalytic asymmetric Mukaiyama–Mannich reaction of fluorinated silyl enol ethers and ketimines is developed, allowing highly enantioselective synthesis of benzosultam based β-fluorinated C^α-tetrasubstituted α-amino acid derivatives.

Asymmetric synthesis of (3S,1'S)-3-(1-amino-2,2,2-trifluoroethyl)-1-(alkyl)-indolin-2-one derivatives by addition of (S)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine to 1-(alkyl)-indolin-2-ones

This paper presents the first study of the addition reactions between amide-derived nucleophiles and chiral CF3-containing N-sulfinyl-imines. We demonstrate that enolates of 1-(alkyl)-indolin-2-ones cleanly react with (S)-N-t-butylsulfinyl-3,3,3-trifluoroacetaldimine affording 3-(1-amino-2,2,2-trifluoroethyl)-1-(alkyl)-indolin-2-ones of (3S,1'S) absolute configuration as the major reaction products with synthetically meaningful diastereoselectivity and chemical yields. The reactions were shown to be of general practical application for preparation of various oxindole derivatives in a diastereomerically pure form.