Generalized access to fluorinated β-keto amino compounds through asymmetric additions of α,α-difluoroenolates to CF3-sulfinylimine

Transient Formation of Hemiketals from Pentafluoro-gem-diols in the Presence of Alcohols

Pentafluoro-gem-diols have emerged as a source of reactive intermediates for synthesizing fluorinated molecules. When pentafluoro-gem-diols were exposed to alcohols as solvents, the formation of transient hemiketals was detected by 19F NMR. The conversion rates to hemiketals were found to be higher with primary alcohols than with secondary or fluorinated alcohols. These findings provide valuable insight for developing novel techniques to construct intricate fluorinated structures using pentafluoro-gem-diols.

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.

Generation of formaldehyde and formaldehyde-d2 for hydroxymethylations and hydroxydeuteromethylations of difluoroenolates and difluorobenzyl carbanions

A method for the in situ production of formaldehyde from dimethylsulfoxide, bromine, and cesium carbonate is reported for reactions with difluoroenolates and difluorobenzyl carbanions. This process also generates formaldehyde-d₂ for the production of 2,2-difluoro-1,1-deuteroethanols. Mechanistic and computational studies further characterize the production of hydroxymethylated and hydroxydeuteromethylated difluorinated organic molecules.

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.

Chiral N-tert-Butylsulfinyl Imines: New Discoveries

In this account the reactions of chiral N-tert-butylsulfinyl imines with organometallic reagents such as organoalkaline (lithium, sodium, potassium and cesium derivatives), organomagnesium, organozinc, organoboron, organoaluminium, organoindium and organosilicon compounds is comprehensively described. The reactivity in all cases is derived to synthetic applications in order to prepare interesting organic nitrogenated molecules, especially in the field of alkaloid compounds.

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.

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.

Controlling the Cleavage of Carbon-Carbon Bonds To Generate α,α-Difluorobenzyl Carbanions for the Construction of Difluoromethylbenzenes

Controlling the cleavage of carbon-carbon bonds during a chemical reaction is a substantial challenge; however, synthetic methods that accomplish this objective produce valuable and often unexplored reactivity. We have designed a mild process to generate α,α-difluorobenzyl carbanions in the presence of potassium carbonate by exploiting the cleavage of C-C bonds during the release of trifluoroacetate. The initiating reagent is potassium carbonate, which represents an improvement over existing protocols that require a strong base. Fragmentation studies across substituted arenes and heteroarenes were conducted along with computational analyses to elucidate reactivity trends. Furthermore, the mildly generated α,α-difluorobenzyl carbanions from electron-deficient aromatics and heteroaromatic rings can react with aldehydes to create derivatives of difluoromethylbenzenes, which are valuable synthetic targets.

Mannich-type addition of 1,3-dicarbonyl compounds to chiral tert-butanesulfinyltrifluoroacetaldimines. Mechanistic aspects and chiroptical studies

Mannich-type addition of 1,3-dicarbonyl compounds to (SS)-N-tert-butanesulfinyltrifluoroacetaldimine has been carried out under dramatically different conditions. The stereochemical outcome was quite different when the reaction was carried out under solvent-free conditions, at high temperature and without any catalyst or additive, compared with the DBU catalyzed reaction in dichloromethane solution at low temperature. Mechanistic aspects of the reaction under both the conditions are discussed. In this respect, vibrational (VCD) and electronic circular dichroism (ECD) and optical rotatory dispersion (ORD) experiments proved to be valuable tools for determining the absolute configurations of the reaction products.

Chemistry of detrifluoroacetylativelyin situgenerated fluoro-enolates

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

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.

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.

Magnesium-Promoted Additions of Difluoroenolates to Unactivated Imines

Although there are many synthetic methods to produce fluorinated and trifluoromethylated organic structures, the construction of difluoromethylated compounds remains a synthetic challenge. We have discovered that unactivated imines will react with difluoroenolates under exceedingly mild conditions when using magnesium salts and organic bases. We have applied this approach to the iminoaldol reaction to produce difluoromethylene groups as α,α-difluoro-β-amino-carbonyl groups. This method provides synthetically useful quantities of difficult to access α,α-difluoro-β-aminoketones without the need of protecting groups or the use of activated imines. Moreover, we have applied this strategy to create analogues of the dual orexin receptor antagonist, almorexant, in only two synthetic steps.

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.

Application of the Pentafluorosulfanyl Group as a Bioisosteric Replacement

The success of fluorinated molecules in drug design has led medicinal chemists to search for new fluorine-containing substituents. A major recently developed group is the pentafluorosulfanyl group. This group is stable under physiological conditions and displays unique physical and chemical properties. There are currently few synthetic methods to install the SF₅ group, yet efforts to integrate this group into lead optimization continue unabated. Typically, the SF₅ group has been used as a replacement for trifluoromethyl, tert-butyl, halogen, or nitro groups. In this review, the use of the SF₅ group as a bioisosteric replacement for each of these three functionalities is compared and contrasted across various groups of biologically active molecules. The organization and presentation of these data should be instructive to medicinal chemists considering to design synthetic strategies to access SF₅ -substituted molecules.

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.

Generation of Magnesium Pentafluoropropen-2-olate from Hexafluoroisopropanol and Synthesis of 2,2,4,4,4-Pentafluoro-3,3-dihydroxyketones

2,2,4,4,4-Pentafluoro-3,3-dihydroxyketones are valuable precursors to difluoroenolates following fragmentation during the release of trifluoroacetate; however, there are few synthetic strategies to prepare this unique class of compound. We addressed this issue and report a mild, two-step synthesis of 2,2,4,4,4-pentafluoro-3,3-dihydroxyketones from aldehydes. Specifically, aldehydes are treated with pentafluoropropen-2-olate, generated from a new fragmentation of hexafluoroisopropanol with a mixed Mg/Li amide, to give pentafluoroalcohols. A subsequent oxidation with Dess-Martin periodinane provides the targets in good isolated yields.

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.

Catalytic Enantioselective and Diastereoselective Allylic Alkylation with Fluoroenolates: Efficient Access to C3-Fluorinated and All-Carbon Quaternary Oxindoles

Synthetically versatile 3,3-disubstituted fluorooxindoles exhibiting vicinal chirality centers were obtained in high yields and with excellent enantio-, diastereo-, and regioselectivity through catalytic asymmetric fluoroenolate alkylation with allylic acetates. The reaction proceeds under mild conditions and can be scaled up without compromising the asymmetric induction. The unique synthetic usefulness of the products is highlighted by the incorporation of additional functionalities and the formation of 3-fluorinated oxindoles exhibiting an array of four adjacent centers of chirality. A new C-F bond functionalization path that provides unprecedented possibilities for the stereoselective generation of a chiral quaternary carbon center in the alkaloid scaffold is introduced.

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

The discovery of detrifluoroacetylative in situ generation of a new type of fluorinated amide enolates derived from 3-fluoroindolin-2-one and their asymmetric Mannich additions with sulfinylaldimines bearing fluoroalkyl groups is reported, which afforded α-fluoro-β-(fluoroalkyl)-β-aminoindolin-2-ones containing C-F quaternary stereogenic centers with excellent yields and high diastereoselectivities.

One-pot synthesis of difluoromethyl ketones by a difluorination/fragmentation process

Difluoromethyl ketones are an under-studied class of ketones which have great potential as useful building blocks for materials and drug design. Here we report a simple and convenient synthesis of this class of compounds via a one-pot difluorination/fragmentation of 1-trifluoromethyl-1,3-diketones which should now allow the chemistry of difluoromethyl ketones to be fully developed.

Optimized Synthesis of a Pentafluoro-gem-diol and Conversion to a CF2Br-Glucopyranose through Trifluoroacetate-Release and Halogenation

Pentafluoro-gem-diols are substrates that enable the synthesis of valuable difluoromethylene-containing organic molecules through the release of trifluoroacetate. Currently, only one synthetic strategy is available to assemble these important precursors. Herein, two new synthetic strategies to a complex pentafluoro-gem-diol are compared to the existing route, and an improved synthetic route has completed. Moreover, the first synthesis of a CF₂Br-glucopyranose was finished by a tandem trifluoroacetate-release halogenation/cyclization protocol.

Asymmetric synthesis of quaternary α-fluoro-β-keto-amines via detrifluoroacetylative Mannich reactions

Efficient asymmetric detrifluoroacetylative Mannich addition reactions between 2-fluoro-1,3-di-ketones/hydrates and chiral N-sulfinyl-imines via C-C bond cleavage were reported, which afforded C-F quaternary α-fluoro-β-keto-amines with excellent yields and high diastereoselectivity.