Cu-Catalyzed Stereoselective Borylation of gem-Difluoroalkenes with B2pin2

Stereodivergent Palladium-Catalyzed C-F Bond Functionalization of gem-Difluoroalkenes

We herein describe a stereodivergent C-F bond functionalization of gem-difluoroalkenes. Using trisubstituted β,β-difluoroacrylates, both E and Z monofluoroalkene products can be obtained with excellent diastereoselectivities. The design of two different reaction manifolds, i.e., Pd(II)- versus Pd(0)-catalyzed cross-coupling of boronic acids, is the key to stereocontrol.

Palladium-Catalyzed Cross-Coupling of gem-Difluorocyclopropanes with gem-Diborylalkanes for the Synthesis of Boryl-Substituted Fluorinated Alkenes

This study presents a novel method for the regioselective coupling of gem-difluorinated cyclopropanes with gem-diborylmethane, utilizing a Pd-catalyst system. This innovative approach enables the synthesis of 2-fluoroalkenyl monoboronate scaffolds with high Z-selectivity. The resulting products undergo further transformations, including oxidation, Suzuki cross-coupling, and trifluoroborylation, all of which are achieved with good yields. This work introduces a valuable synthetic pathway to access important fluorinated compounds for various applications in organic chemistry.

Selective Synthesis of (Z)- and (E)-β-Fluoro-α,β-Unsaturated Amides Using Palladium-Catalyzed Aminocarbonylation

The selective synthesis of (Z)- and (E)-β-fluoro-α,β-unsaturated amides via the palladium-catalyzed aminocarbonylation of 1-fluoro-2,2-diiodovinylarenes is described in the present study. Using {Pd(allyl)Cl}2 as a catalyst and DBU as a base in DMF, the primary product is (Z)-isomers. Conversely, the use of a Xantphos ligand along with {Pd(allyl)Cl}2 and Et3N as the bases in 1,4-dioxane leads to the selective formation of (E)-isomers. Notably, 1-fluoro-2,2-diiodovinylarenes with various substituents on the phenyl ring react with various secondary amines, producing the corresponding (Z)-isomeric amides with a high yield and selectivity. In contrast, (E)-isomeric amides exhibit lower yields and restricted applicability.

Copper and Palladium Cocatalyzed Defluorinative Coupling of gem-Difluoroalkenes and Acyl Chloride

A novel copper and palladium cocatalyzed defluorinative coupling of gem-difluoroalkenes and acyl chlorides has been developed. It is a practical method to prepare α-fluorochalcones, which are a kind of important unit in a variety of bioactive compounds. Under mild reaction conditions, a series of substrates with various functional groups could afford desired products smoothly. Further synthetic studies illustrated that the products of this chemistry could be used as versatile precursors to access complicated compounds. Furthermore, the reaction mechanism was proposed based on control experiments.

Recent Advances in Alkenyl sp2 C-H and C-F Bond Functionalizations: Scope, Mechanism, and Applications

Alkenes and their derivatives are featured widely in a variety of natural products, pharmaceuticals, and advanced materials. Significant efforts have been made toward the development of new and practical methods to access this important class of compounds by selectively activating the alkenyl C(sp²)-H bonds in recent years. In this comprehensive review, we describe the state-of-the-art strategies for the direct functionalization of alkenyl sp² C-H and C-F bonds until June 2022. Moreover, metal-free, photoredox, and electrochemical strategies are also covered. For clarity, this review has been divided into two parts; the first part focuses on currently available alkenyl sp² C-H functionalization methods using different alkene derivatives as the starting materials, and the second part describes the alkenyl sp² C-F bond functionalization using easily accessible gem-difluoroalkenes as the starting material. This review includes the scope, limitations, mechanistic studies, stereoselective control (using directing groups as well as metal-migration strategies), and their applications to complex molecule synthesis where appropriate. Overall, this comprehensive review aims to document the considerable advancements, current status, and emerging work by critically summarizing the contributions of researchers working in this fascinating area and is expected to stimulate novel, innovative, and broadly applicable strategies for alkenyl sp² C-H and C-F bond functionalizations in the coming years.

Theoretical Insight into the Multiple Roles of LiHMDS in Pd-Catalyzed Borylation of Fluorobenzene

Pd-catalyzed borylation of fluorobenzene was theoretically studied. DFT calculations revealed that the reaction occurs through an unprecedented 3 + 6-membered ring transition state, in which one LiHMDS (HMDS = hexamethyldisilazane) acts as a ligand and another LiHMDS is essential to provide Li···N and Li···F interactions, overcoming the large destabilization of the strong phenyl-F bond distortion. The characteristic feature of LiHMDS was elucidated by comparing it with HMDS and NaHMDS analogues.

Enantioselective Copper-Catalyzed sp2/sp3 Diborylation of 1-Chloro-1-Trifluoromethylalkenes

Fluorine-containing organoboron compounds have emerged as novel building blocks in chemical synthesis; among them, fluorinated sp²/sp³ diborylated compounds are particularly appealing, since they might undergo chemoselective and diversified transformations of different C-B bonds with fluorinated functionality, thus bringing versatility and complexity to the eventual products. However, expedient, synthetic strategies for the construction of such fluorinated diborylative compounds are very sparse. Herein, we disclose enantioselective Cu-catalyzed sp²/sp³ diborylations of 1-chloro-1-trifluoromethylalkenes, leading to diborylated compounds bearing a gem-difluoroalkenyl moiety; most intriguingly, the new formed C-B bonds include one stereoselective and optically pure Csp³-B bond. Further transformations on the eventual products demonstrated the values of our presented strategy.

Recent Advances in the Construction of Fluorinated Organoboron Compounds

Fluorinated organoboron compounds are important synthetic building blocks that combine the unique characteristics of a fluorinated motif with the versatile synthetic applications of organoboron moiety. This review article guides the research on fluorinated organoboron compounds mainly from four aspects in recent years: selective monodefluoroborylation of polyfluoroarenes and polyfluoroalkenes, selective borylation of fluorinated substrates, selective fluorination of organoboron compounds, and borofluorination of alkynes/olefins. In addition, this review will provide a necessary guidance and inspiration for the research on the valuable synthetic building block fluorinated organoboron compounds.

Stereodefined alkenes with a fluoro-chloro terminus as a uniquely enabling compound class

Trisubstituted alkenyl fluorides are important compounds for drug discovery, agrochemical development and materials science. Despite notable progress, however, many stereochemically defined trisubstituted fluoroalkenes either cannot be prepared efficiently or can only be accessed in one isomeric form. Here we outline a general solution to this problem by first unveiling a practical, widely applicable and catalytic strategy for stereodivergent synthesis of olefins bearing a fluoro-chloro terminus. This has been accomplished by cross-metathesis between two trisubstituted olefins, one of which is a purchasable but scarcely utilized trihaloalkene. Subsequent cross-coupling can then be used to generate an assortment of trisubstituted alkenyl fluorides. The importance of the advance is highlighted by syntheses of, among others, a fluoronematic liquid-crystal component, peptide analogues bearing an E- or a Z-amide bond mimic, and all four stereoisomers of difluororumenic ester (an anti-cancer compound).

Inorganometallics (Transition Metal-Metalloid Complexes) and Catalysis

While the formation and breaking of transition metal (TM)-carbon bonds plays a pivotal role in the catalysis of organic compounds, the reactivity of inorganometallic species, that is, those involving the transition metal (TM)-metalloid (E) bond, is of key importance in most conversions of metalloid derivatives catalyzed by TM complexes. This Review presents the background of inorganometallic catalysis and its development over the last 15 years. The results of mechanistic studies presented in the Review are related to the occurrence of TM-E and TM-H compounds as reactive intermediates in the catalytic transformations of selected metalloids (E = B, Si, Ge, Sn, As, Sb, or Te). The Review illustrates the significance of inorganometallics in catalysis of the following processes: addition of metalloid-hydrogen and metalloid-metalloid bonds to unsaturated compounds; activation and functionalization of C-H bonds and C-X bonds with hydrometalloids and bismetalloids; activation and functionalization of C-H bonds with vinylmetalloids, metalloid halides, and sulfonates; and dehydrocoupling of hydrometalloids. This first Review on inorganometallic catalysis sums up the developments in the catalytic methods for the synthesis of organometalloid compounds and their applications in advanced organic synthesis as a part of tandem reactions.

Csp3‒H Monofluoroalkenylation via Stereoselective C‒F Bond Cleavage

A practical nickel- and photoredox-catalyzed Csp3‒H monofluoroalkenylation through chelation-assisted Csp2‒F bond cleavage of gem-difluoroalkenes has been developed, which provides an expedient access to the synthesis of tetrasubstituted fluoroalkenes with complete...

Nickel-Catalyzed Stereo- and Enantioselective Cross-Coupling of gem-Difluoroalkenes with Carbon Electrophiles by C-F Bond Activation

Stereo- and enantioselective cross-electrophile coupling involving C-F bond activation is reported. Treatment of gem-difluoroalkenes with racemic benzyl electrophiles in the presence of a chiral nickel complex using B₂ pin₂ as a stoichiometric reductant allows the construction of a C(sp² )-C(sp³ ) bond under mild conditions, affording a broad range of monofluoroalkenes bearing stereogenic allylic centers. Initial mechanistic studies indicate that a radical chain pathway may be operating, wherein the ester group in the gem-difluoroalkene promotes C-F bond activation through oxidative addition to a Ni species.

gem-Heteroatom-Substituted Fluoroalkenes as Mimics of Amide Derivatives or Phosphates: A Comprehensive Review

gem-Heteroatom-substituted fluoroalkenes have received little attention despite their great potential in medicinal chemistry or in fine chemistry. Indeed, due to the electronic and steric similarity between the fluoroalkene moiety and the amide bond as well as the high strength of the carbon-fluorine bond, these gem-heteroatom-substituted fluoroalkenes could be envisioned as stable mimics of various important organic functions, such as phosphates, carbamates, S-thiocarbamates and ureas. We present herein an overview describing the syntheses over the last decade of heteroatom-substituted fluoroalkenes in geminal position. This review will be divided into several sections covering each the common following heteroatom: oxygen-, nitrogen-, sulfur-, phosphorus-, boron- and silicon-substituted fluoroalkenes.

Advances in silylation and borylation of fluoroarenes and gem-difluoroalkenes via C-F bond cleavage

Organoboron and organosilane compounds are widely used in organic synthesis and pharmaceuticals. In addition, the C-F bond functionalization is a useful tool for the construction of carbon-carbon and carbon-heteroatom bonds. In particular, the late-stage functionalization of bioactive molecules through defluoroborylation and defluorosilylation reactions will provide good opportunities for the development and diversification of new medicinal compounds. Thus, this feature article summarized the methods for the defluorosilylation and defluoroborylation of unreactive monofluoroarenes and gem-difluoroalkenes from 2000 to 2021, which might create some new ideas and will be helpful for further research in this field. These defluoroborylation and defluorosilylation strategies can be applied to synthesize silylated arenes, borylated arenes, silylated fluoroalkenes, and borylated fluoroalkenes, thus providing impressive advantages over traditional methods for the synthesis of organoboron and organosilane compounds in terms of divergent structures.

Development of a Concise and Robust Route to a Key Fragment of MCL-1 Inhibitors via Stereoselective Defluoroborylation

MCL-1 is an attractive target for cancer therapy. We recently discovered highly potent and selective MCL-1 inhibitors containing a fluoroalkene fragment for which an efficient route to the main chiral gem-fluoro-BPin fragment was needed. The key step of this synthesis is a highly stereoselective defluoroborylation of a gem-difluorovinyl intermediate. The latter is reached via a copper-catalyzed diastereoselective opening of dimethyloxirane. These two features allowed a 30-fold improvement in yield, a shorter synthesis, and a decrease in the cost of this crucial building block.

Generation of Axially Chiral Fluoroallenes through a Copper-Catalyzed Enantioselective β-Fluoride Elimination

Herein we report the copper-catalyzed silylation of propargylic difluorides to generate axially chiral, tetrasubstituted monofluoroallenes in both good yields (27 examples >80%) and enantioselectivities (82-98% ee). Compared to previously reported synthetic routes to axially chiral allenes (ACAs) from prochiral substrates, a mechanistically distinct reaction has been developed: the enantiodiscrimination between enantiotopic fluorides to set an axial stereocenter. DFT calculations and vibrational circular dichroism (VCD) suggest that β-fluoride elimination from an alkenyl copper intermediate likely proceeds through a syn-β-fluoride elimination pathway rather than an anti-elimination pathway. The effects of the C1-symmetric Josiphos-derived ligand on reactivity and enantioselectivity were investigated. Not only does this report showcase that alkenyl copper species (like their alkyl counterparts) can undergo β-fluoride elimination, but this elimination can be achieved in an enantioselective fashion.

Rh-catalyzed tunable defluorinative borylation

Described herein is a Rh-catalyzed tunable defluorinative borylation of allylic gem-difluorides to provide allylborylated monofluoroalkenes or homoallylborylated monofluoroalkenes with excellent Z/E selectivities. Completely different reaction paths were observed by slightly changing the reaction conditions. Allylborylated monofluoroalkenes were further converted into dihydroxyl-containing monofluoroalkenes.

Iron-Catalyzed Diborylation of Unactivated Aliphatic gem-Dihalogenoalkenes: Synthesis of 1,2-Bis(boryl)alkanes

Herein, we report the first example of iron-catalyzed defluoroborylation of unactivated gem-difluoroalkenes, gem-dichloroalkenes, and gem-dibromoalkenes, providing the 1,2-bis(boryl)alkanes in moderate to good yield. This transformation has high regioselectivity, wide substrate scope, and excellent functional group compatibility. Preliminary mechanistic studies indicate that double β-F elimination is involved in the catalytic cycle, and the 1,1-diborylated alkenes might be intermediates in this iron-catalyzed 1,2-diborylation reaction.

Stereoselective Synthesis of Difluorinated 1,3-Dienes via Palladium-Catalyzed C-F Bond Activation of Tetrasubstituted gem-Difluoroalkenes

A highly diastereoselective Pd(0)-catalyzed synthesis of difluorinated 1,3-dienes is described. Symmetrical 1,3-dienes containing a vicinal difluoro moiety can be obtained as single diastereomers from tetrasubstituted gem-difluoroalkenes. The reaction presumably proceeds through a stereoselective twofold Pd-catalyzed Miyaura borylation/Suzuki-Miyaura cross-coupling of the C-F bond. Moreover, modular synthesis of unsymmetrical difluorinated 1,3-dienes is also achievable by the coupling between gem-difluoroalkenes and borylated monofluoroalkenes.

Pd/Cu-Catalyzed Defluorinative Carbonylative Coupling of Aryl Iodides and gem-Difluoroalkenes: Efficient Synthesis of α-Fluorochalcones

An unprecedented and challenging defluorinative carbonylation was achieved. Enabled by a Pd/Cu cooperative catalyst system, the first example of defluorinative carbonylative coupling has been established. With gem-difluoroalkenes and aryl iodides as the substrates, this methodology offers flexible and facile access to privileged α-fluorochalcones under mild reaction conditions in moderate-to-excellent yields. Mechanistic studies indicated transmetalation between palladium and copper intermediates as a crucial step of the catalytic cycle.

Experimental and Computational Studies of the Iron-Catalyzed Selective and Controllable Defluorosilylation of Unactivated Aliphatic gem-Difluoroalkenes

The first iron-catalyzed defluorosilylation of unactivated gem-difluoroalkenes was developed, delivering gem-disilylated alkenes and (E)-silylated alkenes with excellent efficiency. This protocol features good functional group compatibility and excellent regio- and stereoselectivity, enabling the late-stage silylation of biologically relevant compounds, thus providing good opportunities for applications in medicinal chemistry. Preliminary mechanistic studies and DFT calculations reveal that a nucleophilic addition and elimination of the second C-F bond might be involved in the disilylation catalytic system, demonstrating unusual reactivity characteristics of iron catalysis.

Convergent Synthesis of Fluoroalkenes Using a Dual-Reactive Unit

Fluoroalkenes have shown importance as a metabolically stable isostere of amide compounds. To expedite the synthesis of diverse fluoroalkenes, we have developed a dual-reactive C2-unit, (Z)-1-boryl-1-fluoro-2-tosyloxyethene, containing nucleophilic and electrophilic moieties. Consecutive palladium-catalyzed cross-coupling reactions of this unit with aryl bromides and aryl boronic acids allow for the convergent synthesis of diverse trans-1,2-diaryl-substituted fluoroethenes in a chemoselective and stereoretentive manner.

Nickel-catalyzed defluorinative alkylation of C(sp2)–F bonds

A nickel-catalyzed defluorinative alkylation of unactivated C(sp²)–F electrophiles using commercially available trialkylaluminum reagents, thus forming the C(sp²)–C(sp³) bonds is reported.

Autocatalytic Synthesis of Thioesters via Thiocarbonylation of gem-Difluoroalkenes

Herein, we report a new method for the synthesis of acyethanethioates via thiocarbonylation of gem-difluoroalkenes with thiols. This reaction provides a new pathway to prepare thioesters under mild conditions without the use of any additives. Mechanistic studies revealed that in situ generated HF facilitated the C-F bond cleavage in an autocatalytic manner.

A mechanistic study on Cu(i) catalyzed carboxylation of the C-F bond with CO2: a DFT study

The Cu(i) catalyzed carboxylation of the C-F bond recently reported by Yu and co-workers is an excellent method for the construction of complex fluoroacrylate compounds with high regioselectivity. In the present study, theoretical calculations were carried out to investigate the detailed mechanism of the catalytic cycle and the origin of regioselectivity. The calculation results reveal that the overall catalytic cycle proceeds via the migratory insertion of difluoroalkene on the boryl-Cu(i) species, synβ-F elimination, transmetalation, and carboxylation steps. The rate determining step is the carboxylation step, and the migration insertion is the regioselectivity determining step. The regioselectivity for 2,1-insertion is consistent with Yu's experiment, and is determined by both steric and electronic effects.

Cobalt-Catalyzed Defluorosilylation of Aryl Fluorides via Grignard Reagent Formation

Transition-metal-catalyzed transformations of the carbon-fluorine bond not only tackle an interesting problem of challenging bond activation but also offer new synthetic strategies where the relatively inert C-F bond is converted to versatile functional groups. Herein we report a practical cobalt-catalyzed silylation of aryl fluorides that uses a cheap electrophilic silicon source with magnesium. This method is compatible with various silicon sources and can be operated under aerobic conditions. Mechanistic studies support the in situ formation of a Grignard reagent, which is captured by the electrophilic silicon source.

Cobalt-Catalyzed Selective Unsymmetrical Dioxidation of gem-Difluoroalkenes

gem-Difluoroalkenes represent valuable synthetic handles for organofluorine chemistry; however, most reactions of this substructure proceed through reactive intermediates prone to eliminate a fluorine atom and generate monofluorinated products. Taking advantage of the distinct reactivity of gem-difluoroalkenes, we present a cobalt-catalyzed regioselective unsymmetrical dioxygenation of gem-difluoroalkenes using phenols and molecular oxygen, which retains both fluorine atoms and provides β-phenoxy-β,β-difluorobenzyl alcohols. Mechanistic studies suggest that the reaction operates through a radical chain process initiated by Co(II)/O₂/phenol and quenched by the Co-based catalyst. This mechanism enables the retention of both fluorine atoms, which contrasts most transition-metal-catalyzed reactions of gem-difluoroalkenes that typically involve defluorination.

Methodologies and Strategies for Selective Borylation of C-Het and C-C Bonds

Organoborons have emerged as versatile building blocks in organic synthesis to achieve molecular diversity and as carboxylic acid bioisosteres with broad applicability in drug discovery. Traditionally, these compounds are prepared by the substitution of Grignard/lithium reagents with electrophilic boron species and Brown hydroboration. Recent developments have provided new routes for the efficient preparation of organoborons by applying reactions using chemical feedstocks with leaving groups. As compared to the previous methods that used organic halides (I, Br, and Cl), the direct borylation of less reactive C-Het and C-C bonds has become highly important to get efficiency and functional-group compatibility. This Review aims to provide a comprehensive overview of this topic, including (1) C-F bond borylation, (2) C-O bond borylation, (3) C-S bond borylation, (4) C-N bond borylation, and (5) C-C bond borylation. Considerable attention is given to the strategies and mechanisms involved. We expect that this Review will inspire chemists to discover more efficient transformations to expand this field.

Recent Advances in Transition Metal-Catalyzed Functionalization of gem-Difluoroalkenes

gem-Difluorinated alkenes are readily accessible building blocks that can undergo functionalization to provide a broad spectrum of fluorinated and non-fluorinated products. Herein, we review recent (since 2017) transition metal-catalyzed transformations of these specialized alkenes and summarize general reactivity patterns of these reactions. Many transition metal-catalyzed reactions undergo net C-F bond functionalization reactions to deliver monofluorinated products. These reactions typically proceed through β-fluoro alkylmetal intermediates that readily eliminate a β-fluoride to deliver monofluoroalkene products. A second series of reactions exploit coinage metal fluorides to add F- to the gem-difluorinated alkene, and further functionalization delivers trifluoromethyl-containing products. In stark contrast, few transition metal-catalyzed reactions proceed in net "fluorine-retentive processes" to deliver difluoromethylene-based products.