Detrifluoroacetylative in Situ Generation of Free 3-Fluoroindolin-2-one-Derived Tertiary Enolates: Design, Synthesis, and Assessment of Reactivity toward Asymmetric Mannich Reactions

Synthesis of Tetrahydro-indolones through Rh(III)-Catalyzed [3 + 2] Annulation of Enaminones with Iodonium Ylides

An unprecedented protocol for a Rh(III)-catalyzed [3 + 2] annulation from simple and readily available enaminones and iodonium ylides has been developed. The novel strategy allows for access to a new class of structurally diverse tetrahydro-indolones with high efficiency and a broad substrate scope. In addition, this transformation represents the first example of the selective Rh(III)-catalyzed alkenyl C-H bond functionalization and annulation of enaminones. Finally, the potential applications of this protocol are demonstrated through gram-scale reaction and late-stage modification.

Cascade Detrifluoroacetylation, C-S Bond Cleavage, and SN2' Reaction of α,α-Difluorinated Gem-Diols with MBH Esters

A new SN2' reaction type of Morita-Baylis-Hillman (MBH) ester with sulfonyl anion, generated in situ via detrifluoroacetylation as a nucleophile is developed. Experimental results and DFT calculations disclose that the reaction proceeds via C-C bond cleavage to generate a PhSO2CF2 anion, C-S bond cleavage to generate a sulfonyl anion with the release of CF2 carbene, and an SN2' reaction with the MBH ester. The reaction features operational simplicity, wide substrate scope, high yields, and excellent stereoselectivity, which represents a new reaction mode of fluorinated gem-diols and also provides an efficient way to obtain β,γ-unsaturated sulfones.

Divergent Reaction of Activated Pyridines with α,α-Difluorinated gem-Diols: Regioselective Synthesis of gem-Difluorinated Dihydropyridines and Dihydropyridones

The nucleophilic reactivity of α,α-difluorinated gem-diols toward activated pyridinium salts has been capitalized in a highly regioselective fashion, offering biologically relevant 1,4-dihydropyridines and 3,4-dihydro-2-pyridones adorned with the valuable gem-difluoromethylene motif. The protocol is scalable as well as high yielding and accommodates a broad range of substrates and functional groups. Additionally, the synthesis of difluorinated oxa-azabicyclo[3.3.1]nonane frameworks has been showcased through product diversification.

Synthesis of oxindoles bearing a stereogenic 3-fluorinated carbon center from 3-fluorooxindoles

3,3-Disubstituted oxindoles bearing a stereogenic 3-fluorinated carbon center are privileged structural motifs present in many bioactive molecules. The straightforward functionalization of 3-fluorooxindoles constitutes a powerful method for the synthesis of 3-fully substituted 3-fluorooxindoles, taking advantage of the ease of preparation of 3-fluorooxindoles with different substitution patterns and the atom efficiency of chemical reactions. In the past decade, many papers have appeared on the synthesis of 3-fully substituted 3-fluorooxindoles from 3-fluorooxindoles. Importantly, many asymmetric catalytic methods have been developed for the enantioselective synthesis of these valuable compounds. This review summarizes the achievements in this area, and overviews synthetic opportunities that still exist.

Synthesis of Isothiazoles through N-Propargylsulfinylamide: TFA-Promoted Sulfinyl Group-Involved Intramolecular Cyclization

A new reactivity mode of tert-butanesulfinamide has been developed, which proceeds through C-S and O-S bond cleavage of N-propargyl tert-butanesulfinylamide allowing rapid assembly of poly functionalized isothiazoles. This intramolecular cyclization reaction could be conducted under mild and convenient conditions and tolerates several fluoroalkyl and substituted phenyl groups with good chemical yields. This reaction not only represents a new reactivity of tert-butanesulfinamide but also provides an easy strategy for the synthesis of isothiazoles.

Catalytic stereoselective Mannich-type reactions for construction of fluorinated compounds

For its unique role in developing and designing new bioactive materials and healthcare products, fluoro-organic compounds have attracted remarkable interest. Along with ever-increasing demand for a wider availability of fluorine-containing structural units, a large diversity of methods has been introduced to incorporate fluorine atoms specially in a stereoselective fashion. Among them, catalytic Mannich reaction can proceed with a broad variety of reactants and open clear paths for the synthesis of versatile amine synthons in the synthesis of natural product and pharmaceutical molecules. This review provides an overview of the employment of catalytic asymmetric Mannich reactions in the synthesis of fluorine-containing amine compounds and highlights the conceivable distinct mechanisms.

Vicinal difunctionalization of carbon-carbon double bond for the platform synthesis of trifluoroalkyl amines

Regioselective vicinal diamination of carbon-carbon double bonds with two different amines is a synthetic challenge under transition metal-free conditions, especially for the synthesis of trifluoromethylated amines. However, the synthesis of ethylene diamines and fluorinated amine compounds is demanded, especially in the pharmaceutical sector. Herein, we demonstrate that the controllable double nucleophilic functionalization of an activated alkene synthon, originated from a trifluoropropenyliodonium salt with two distinct nucleophiles, enables the selective synthesis of trifluoromethylated ethylene amines and diamines on broad scale with high efficiency under mild reaction conditions. Considering the chemical nature of the reactants, our synthetic approach brings forth an efficient methodology and provides versatile access to highly fluorinated amines.

Asymmetric Mannich reactions of (S)-N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimines with yne nucleophiles

In the present work, arylethynes were studied as new C-nucleophiles in the asymmetric Mannich addition reactions with (S)-N-tert-butylsulfinyl-3,3,3-trifluoroacetaldimine. The reactions were conducted under operationally convenient conditions affording the corresponding Mannich adducts with up to 87% yield and 70:30 diastereoselectivity. The isomeric products can be separated using regular column chromatography to afford diastereomerically pure compounds. The purified Mannich addition products were deprotected to give the target enantiomerically pure trifluoromethylpropargylamines. A mechanistic rationale for the observed stereochemical outcome is discussed.

Merging Electrosynthesis and Bifunctional Squaramide Catalysis in the Asymmetric Detrifluoroacetylative Alkylation Reactions

An enantioselective bifunctional squaramide-catalyzed detrifluoroacetylative alkylation reaction has been developed under electrochemical conditions. The unified strategy based on this key tandem methodology has been divergently explored for the asymmetric synthesis of fluorine-containing target molecules with good stereocontrol (up to 95 % ee). Furthermore, this asymmetric catalytic reaction combines the benefits of electrosynthesis and organocatalysis for the preparation of biologically relevant products containing C-F tertiary stereogenic centers.

Detrifluoroacetylative in Situ Generated Cyclic Fluorinated Enolates for the Preparation of Compounds Featuring a C-F Stereogenic Center

Practical methods for the preparation of selectively fluorinated compounds are in extremely high demand in nearly every sector of the pharmaceutical and agrochemical industries. Here we provided an account of the recent methodological breakthrough dealing with detrifluoroacetylative in situ generation of cyclic fluoro-enolates and their application for the preparation of various polyfunctional compounds featuring quaternary C-F stereogenic carbon. The reactions include aldol, Mannich, Michael addition reactions, S_N2/S_N2' alkylations, and the additions to azo compounds. The detrifluoroacetylative protocol for in situ generation of cyclic fluoro-enolates is operationally simple and scalable and proceeds at ambient temperature. Generally, the stereochemical outcome, controlled by the stoichiometric chiral auxiliary of the chiral catalyst, is synthetically useful, allowing preparation of enantiomerically pure compounds of high pharmaceutical potential.

Organocatalytic Asymmetric Mannich Addition of 3-Fluorooxindoles to Dibenzo[b,f][1,4]oxazepines: Highly Enantioselective Construction of Tetrasubstituted C-F Stereocenters

3-Fluorooxindoles and the dibenzo[b,f][1,4]oxazepane scaffolds are important pharmacophores that have important application in medicinal chemistry. An organocatalyzed asymmetric Mannich reaction of 3-fluorooxindoles with dibenzo[b,f][1,4]oxazepines affording various seven-member cyclic amines containing chiral tetrasubstituted C-F stereocenters was developed. These reactions which were catalyzed by a bifunctional Cinchona alkaloid-derived thiourea catalyst afforded a wide range of substrates in moderate to high yields with excellent diastereo- and enantioselectivities (up to 88% yield, >20:1 dr and >99% ee). A feasible reaction mechanism was also proposed.

Enantioselective Mannich Reactions of 3-Fluorooxindoles with Cyclic N-Sulfamidate Aldimines

Both the 3-fluorooxindole and cyclic sulfamidate frameworks are important in medicinal chemistry owing to their associated biological activities. We report an approach accessing 3-fully substituted 3-fluorooxindoles, containing a benzo-fused sulfamidate subunit through highly enantioselective Mannich-type reactions between 3-fluorooxindoles and cyclic benzo-fused N-sulfamidate aldimines. These reactions are promoted by a commercially available cinchona alkaloid catalyst, accommodate a broad substrate scope, and deliver the desired products in a yield of up to 99% with an enantiomeric excess of up to 94%. A plausible reaction pathway is also presented.

Organocatalytic asymmetric syntheses of 3-fluorooxindoles containing vicinal fluoroamine motifs

An organocatalytic Mannich reaction of 3-fluorooxindoles has been developed. Using a commercially available cinchona alkaloid catalyst, a wide range of 3-fluorooxindoles was successfully reacted with N-sulfonyl aldimines to give biologically important 3-fluorooxindoles containing vicinal fluoroamine motifs with high efficiency and good enantioselectivity. This protocol uses readily available reactants and cheap organocatalysts, and it is operationally simple.

Synthesis of 3-substituted 3-fluoro-2-oxindoles by deacylative alkylation

The fluorination of 3-acetyl-2-oxindoles with N-fluorobenzenesulfonimide under Lewis acid catalysis using Mg(ClO4)2 gives the starting compounds 3-acetyl-3-fluoro-2-oxindoles. These compounds are subjected to base-promoted deacylative alkylation (DaA) for the in situ generation of 3-fluoro-2-oxindole enolates under very mild reaction conditions using Triton B (1 equiv.) and alkyl halides and Michael acceptors as electrophilic reagents. The corresponding 3-alkylated-3-fluoro-2-oxindoles are obtained in good to very high yields. In addition, the palladium-catalyzed deacylative allylation is carried out with allylic alcohols using LiOtBu as the base and 6 mol% of Pd(OAc)2 and dppp, giving the resulting 3-allylated 3-fluoro-2-oxindoles in good yields. This methodology allows a simple synthesis of 3-alkylated-3-fluoro-2-oxindoles, which are difficult to obtain by other routes.

Chemistry of detrifluoroacetylativelyin situgenerated fluoro-enolates

This review article provides a summary of the detrifluoroacetylativein situgeneration of fluorine-containing enolates and their related reactions.

Divergent Reactivity of gem-Difluoro-enolates toward Nitrogen Electrophiles: Unorthodox Nitroso Aldol Reaction for Rapid Synthesis of α-Ketoamides

An amination reaction of in situ generated gem-difluoro-enolates has been explored with electrophilic nitrogen sources. While their exposure to azodicarboxylates smoothly produced fluorinated α-amino ketones, reaction with nitrosoarenes (nitroso aldol reaction) furnished α-ketoamides in very high yields (up to 94%). The reaction is very fast (typically completed within 5 min) and scalable and tolerates various sensitive functional groups. Synthetic utility of this process was highlighted through the production of diverse nitrogen heterocycles and an orexin receptor antagonist.

Palladium-Catalyzed Asymmetric Allylic Alkylations of Colby Pro-Enolates with MBH Carbonates: Enantioselective Access to Quaternary C-F Oxindoles

Owing to the innovative applications of fluorinated compounds in many areas of technology and medicine, methods for the preparation of C-F quaternary fluorine containing compounds are in extremely high demand. Here, we report the discovery of a general procedure for an S_N 2 reaction catalyzed by Pd/Ding-SKP-type ligands, and that occurs between Colby pro-enolates with MBH carbonates to afford the corresponding products featuring two consecutive stereogenic carbons, including a C-F quaternary stereogenic center. The reactions readily occur at ambient temperatures with high chemical yields and in excellent chemo-, diastereo- and enantioselective manners. This practically attractive stereochemical outcome, coupled with the operational simplicity and structural generality, bodes well for the synthetic application of this process in the preparation of a novel class of biologically relevant fluorine-containing compounds.

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.

Catalytic asymmetric aldol addition reactions of 3-fluoro-indolinone derived enolates

Reported herein is a Cu(i)/bisoxazoline ligand-catalyzed aldol reaction of unprotected tertiary enolates generated in situ from 3-(1,1-dihydroxy-2,2,2-trifluoroethyl)-substituted derivatives of 3-fluoro-2-oxindoles. A range of α-fluoro-β-aryl/hetaryl/alkyl-β-hydroxy-indolin-2-ones containing C-F quaternary stereogenic centers of high pharmaceutical importance were furnished in good yields and satisfactory diastereo- and enantioselectivities. The reactions were conducted under operationally convenient conditions and displayed wide substrate/functional group generality including unprotected N-H on the tertiary enolates, and aromatic, hetero-aromatic and aliphatic aldehydes.

Organocatalytic Asymmetric Synthesis of α-Oxetanyl and α-Azetidinyl Tertiary Alkyl Fluorides and Chlorides

Asymmetric thiourea and squaramide catalysis provides access to synthetically versatile α-oxetanyl and α-azetidinyl alkyl halides exhibiting a tetrasubstituted chiral carbon center with high yields and enantioselectivities. The products are readily transformed with negligible erosion of enantiopurity and excellent diastereoselectivity to a diverse group of multifunctional compounds including fluorooxindoles with two contiguous chirality centers, fluorinated heterocyclic spiranes, and polyspiro compounds.

Organocatalytic Stereoselective Synthesis of Fluorinated 3,3'-Linked Bisoxindoles

A highly diastereoselective organocatalytic method that produces 3-fluoro-3'-hydroxy-3,3'-bisoxindoles and the corresponding 3-fluoro-3'-amino derivatives having two adjacent chirality centers from fluorooxindoles and isatins in high yields is described. The reaction occurs in protic solvents at room temperature, it can be upscaled without compromising yield and stereoselectivity, and chromatographic product purification is not required.

Stereoselective Synthesis of 3,3'-Bisindolines by Organocatalytic Michael Additions of Fluorooxindole Enolates to Isatylidene Malononitriles in Aqueous Solution

A highly diastereoselective organocatalytic reaction for the synthesis of fluorinated 3,3'-bisindolines exhibiting adjacent tetrasubstituted carbon stereocenters is described. A broad variety of heterochiral bisindolines was prepared in 91-99% yield using 3-fluorooxindoles and isatylidene malononitriles in the presence of catalytic amounts of triethylamine in water or aqueous solution. The reaction can be upscaled without compromising yield and diastereoselectivity and the general usefulness of this method was demonstrated with various Michael acceptors and extended to aldol and Mannich reactions.

Chemoselective SN2' Allylations of Detrifluoroacetylatively In Situ Generated 3-Fluoroindolin-2-one-Derived Tertiary Enolates with Morita-Baylis-Hillman Carbonates

The first example of the S_N2' reaction type of the detrifluoroacetylatively in situ generated tertiary fluoro-enolates in the uncatalyzed reactions with Morita-Baylis-Hillman derivatives has been described. The S_N2' substitution takes place in a highly chemoselective manner as no corresponding S_N2 products were observed in the reaction mixtures. Due to the excellent stereochemical outcome, the reactions seem to have an apparent synthetic value for the preparation of structurally new fluorinated oxindoles.

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.

Asymmetric synthesis of C–F quaternary α-fluoro-β-amino-indolin-2-ones via Mannich addition reactions; facets of reactivity, structural generality and stereochemical outcome

An asymmetric detrifluoroacetylative Mannich reaction between in situ generated tertiary enolates and sulfinyl-imines has been explored. The reaction provides a new access to α-fluoro-β-amino-indolin-2-ones with tetrasubstituted fluorinated stereogenic center.

Metal-free nitroxyl radical-mediated β-C(sp3)–H amination of saturated ketones with heteroaryl halides: multiple roles of TEMPO

The first metal-free nitroxyl-radical-mediated β-amination of saturated ketones by using heteroaryl halides as amide precursors has been developed.