Copper-mediated fluoroalkylation reactions with iododifluoroacetamides: controlling the selectivity among cross-coupling, intramolecular cyclization, and homocoupling reactions

The Progress of Reductive Coupling Reaction by Iron Catalysis

The transition metal catalyzed coupling reaction has revolutionized the strategies for forging the carbon-carbon bonds. In contrast to traditional cross-coupling methods using pre-prepared nucleophilic organometallic reagents, reductive coupling reactions for the C-C bonds formation provide some advantages. Because both coupling partners are reduced in the final products using a stoichiometric amount of a reductant, this approach not only avoids the need to use sensitive organometallic species, but also provides an orthogonal and complementary access to classical coupling reaction. Notably, the reductive coupling reactions feature readily available fragments, promote good step economy, exhibit high functional group tolerance and unique chemoselectivity, which have propelled their increasingly popular in the organic synthesis. In recent years, due to the low price, minimal toxicity, and environmentally benign character, iron-catalyzed carbon-carbon coupling reactions have garnered significant attention from the organic synthetic chemists and pharmacologists, especially the iron-catalyzed reductive coupling. This review aims to provide an insightful overview of recent advances in iron-catalyzed reductive coupling reactions, and to illustrate their possible reaction mechanisms.

Synthetic strategies for the construction of C3-fluorinated oxindoles

C3-fluorinated oxindoles are important scaffolds known to demonstrate various biological properties. As bio-isosteres of oxindoles, these compounds have shown tremendous potential in drug research discovery programs. Besides, they also serve as starting materials for synthesizing other fluorine-containing new architectures, thus launching research for developing new methods for their synthesis. Consequently, various approaches have been developed over the years to synthesize C3-fluorinated oxindoles. This review highlights the strategies developed to date to access C3-difluoro and monofluorooxindoles via intermolecular and intramolecular approaches. The key findings of the strategies developed are discussed along with the prevailing mechanism.

Catalytic Radical-Triggered Annulation/Iododifluoromethylation of Enynones for the Stereospecific Synthesis of 1-Indenones

A new Pd(II)-catalyzed annulation/iododifluoromethylation of enynones has been developed for the synthesis of versatile 1-indanones with moderate to good yields (26 examples). The present strategy enabled the concomitant incorporation of two important difluoroalkyl and iodo functionalities into 1-indenone skeletons with (E)-stereoselectivity. The mechanistic pathway was proposed, consisting of the difluoroalkyl radical-triggered α,β-conjugated addition/5-exo-dig cyclization/metal radical cross-coupling/reductive elimination cascade.

Stereoselective synthesis of fluoroalkylated (Z)-alkene via nickel-catalyzed and iron-mediated hydrofluoroalkylation of alkynes

An efficient nickel-catalyzed, iron-mediated hydrofluoroalkylation of alkynes with bromodifluoroacetate or perfluoroalkyl iodide, which proceeded smoothly to give fluoroalkylated (Z)-alkenes with high stereocontrol (up to 99 : 1 Z/E), was developed.

Utilization of Unsymmetric Diaryliodonium Salts in α-Arylation of α-Fluoroacetoacetamides

The use of unsymmetric diaryliodonium salts as a versatile class of arylating agents has been demonstrated by developing a novel strategy to quickly access α-arylated α-fluoroacetoacetamides. The protocol provides a convenient metal-free method for the α-arylation of a diverse class of fluorinated acetoacetamides, and the products are obtained in good yields. The strategy, upon use of electron-deficient diaryliodonium salts as an arylating agent, provides α-fluoroacetamides through a spontaneous arylation/deacylation cascade.

The Fascinating Chemistry of α-Haloamides

The aim of this review is to highlight the rich chemistry of α-haloamides originally mainly used to discover new C-N, C-O and C-S bond forming reactions, and later widely employed in C-C cross-coupling reactions with C(sp3), C(sp2) and C(sp) coupling partners. Radical-mediated transformations of α-haloamides bearing a suitable located unsaturated bond has proven to be a straightforward alternative to access diverse cyclic compounds by means of either radical initiators, transition metal redox catalysis or visible light photoredox catalysis. On the other hand, cycloadditions with α-halohydroxamate-based azaoxyallyl cations have garnered significant attention. Moreover, in view of the important role in life and materials science of difluoroalkylated compounds, a wide range of catalysts has been developed for the efficient incorporation of difluoroacetamido moieties into activated as well as unactivated substrates.

Metal-free α-arylation of α-fluoro-α-nitroacetamides employing diaryliodonium salts

Herein, we present a mild and efficient metal-free arylation of α-fluoro-α-nitroacetamides employing diaryliodonium salts. A broad range of diaryliodonium salts and α-fluoro-α-nitroacetamides containing sensitive functional groups was successfully employed in this protocol to yield the arylated products in good yields. The synthetic value of this novel protocol was further highlighted by extending the α-arylation to α-cyano-α-fluoroacetamides.

Palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones: synthesis of alkene-functionalized oxindoles

An efficient approach for the construction of alkene-functionalized oxindoles was developed via palladium-catalyzed cascade reactions of alkene-tethered carbamoyl chlorides with N-tosyl hydrazones.

Copper-mediated cascade radical cyclization of olefins with naphthalenyl iododifluoromethyl ketones

Copper-mediated radical cyclization of naphthalenyl iododifluoromethyl ketones with olefins was developed to generate a series of unprecedented gem-difluorodihydrophenanthrenones with excellent regioselectivity.

Regenerative Glycosylation

Previously, we communicated 3,3-difluoroxindole (HOFox)-mediated glycosylations wherein 3,3-difluoro-3H-indol-2-yl (OFox) imidates were found to be key intermediates. Both the in situ synthesis from the corresponding glycosyl bromides and activation of the OFox imidates could be conducted in a regenerative fashion. Herein, we extend this study to the synthesis of various glycosidic linkages using different sugar series. The main outcome of this study relates to enhanced yields and/or reduced reaction times of glycosylations. The effect of HOFox-mediated reactions is particularly pronounced in case of unreactive glycosyl donors and/or glycosyl acceptors. A multistep regenerative synthesis of oligosaccharides is also reported.

Copper-mediated regioselective hydrodifluoroalkylation of alkynes

A highly regioselective copper-mediated hydrodifluoroalkylation of alkynes with ethyl bromodifluoroacetate or bromodifluoroacetamides has been developed.

Nickel-catalyzed direct difluoromethylation of aryl boronic acids with BrCF2H

Nickel-catalyzed direct difluoromethylation of aryl boronic acids has been developed with the industrial raw material BrCF₂H.

Synthesis of 3-CF2-Containing Chromones via a Visible-Light-Induced Radical Cascade Reaction of o-Hydroxyaryl Enaminones

A general and efficient visible-light-induced CF₂ radical-based cascade reaction of o-hydroxyaryl enaminones has been described. This protocol afforded the corresponding functionalized 3-CF₂-containing chromones in generally good yields under mild reaction conditions. The use of NaHSO₃, which has both basicity and reducibility, efficiently suppressed the formation of two byproducts, 4H-chromen-4-one and 3-bromo-4H-chromen-4-one.

OFox imidates as versatile glycosyl donors for chemical glycosylation

Previously we communicated 3,3-difluoroxindole (HOFox) - mediated glycosylations wherein 3,3-difluoro-3H-indol-2-yl (OFox) imidates were found to be key intermediates. Both the in situ synthesis from the corresponding glycosyl bromides and activation of the OFox imidates could be conducted in a regenerative fashion. Herein, we extend this study with the main focus on the synthesis of various OFox imidates and their investigation as glycosyl donors for chemical 1,2-cis and 1,2-trans glycosylation.

Copper/B2pin2-catalyzed C–H difluoroacetylation–cycloamidation of anilines leading to the formation of 3,3-difluoro-2-oxindoles

An original and efficient synthesis of 3,3-difluoro-2-oxindole derivatives has been developed via copper/B₂pin₂-catalyzed difluoroacetylation of aniline via C–H activation followed by intramolecular amidation.

Ag(i)-Catalyzed oxidative decarboxylation of difluoroacetates with activated alkenes to form difluorooxindoles

A silver-catalyzed oxidative decarboxylative gem-difluoromethylenation of difluoroacetates with activated alkenes to gem-difluoromethylenated oxindoles.

Copper-catalyzed gem-difluoromethylenation of C(sp2)–H bonds of alkenes

Copper-catalyzed gem-difluoromethylenation of the C(sp²)–H bonds of alkenes has been developed. This protocol is the first to efficiently achieve gem-difluoromethylenation of C(sp²)–H bonds of unactivated aliphatic terminal olefins and is applied in gem-difluoromethylenation/cyclization of alkenes.

Synthesis of 2-oxindoles via 'transition-metal-free' intramolecular dehydrogenative coupling (IDC) of sp(2) C-H and sp(3) C-H bonds

The synthesis of a variety of 2-oxindoles bearing an all-carbon quaternary center at the pseudo benzylic position has been achieved via a ‘transition-metal-free’ intramolecular dehydrogenative coupling (IDC). The construction of 2-oxindole moieties was carried out through formation of carbon–carbon bonds using KOt-Bu-catalyzed one pot C-alkylation of β-N-arylamido esters with alkyl halides followed by a dehydrogenative coupling. Experimental evidences indicated toward a radical-mediated path for this reaction.

Synthesis of 3-fluoroalkenyl-3-trifluoromethyl-2-oxindoles by the reaction of indoline-2,3-diones with difluoromethylene phosphabetaine

An unprecedent reaction of indoline-2,3-diones and (triphenylphosphonio)difluoroacetate (PDFA) afforded novel 3-fluoroalkenyl-3-trifluoromethyl-2-oxindoles in moderate to excellent yields. These products could be transformed into other trifluoromethylated oxindole derivatives.

Synthesis of Aryldifluoroamides by Copper-Catalyzed Cross-Coupling

A copper-catalyzed coupling of aryl, heteroaryl, and vinyl iodides with α-silyldifluoroamides is reported. The reaction forms α,α-difluoro-α-aryl amides from electron-rich, electron-poor, and sterically hindered aryl iodides in high yield and tolerates a variety of functional groups. The aryldifluoroamide products can be transformed further to provide access to a diverse array of difluoroalkylarenes, including compounds of potential biological interest.

Visible-light photoredox intramolecular difluoroacetamidation: facile synthesis of 3,3-difluoro-2-oxindoles from bromodifluoroacetamides

We report an operationally simple, visible-light-driven protocol for intramolecular C-H difluoroacetamidation of arenes for the synthesis of biologically relevant 3,3-difluoro-2-oxindoles at room temperature. Using fac-Ir(ppy)3 as a photocatalyst and a 3 W blue LED as a light source, an array of difluoroxindoles was prepared from rapidly available tertiary aryl bromodifluoroacetamides in moderate to excellent yields.

Copper-mediated aerobic (phenylsulfonyl)difluoromethylation of arylboronic acids with difluoromethyl phenyl sulfone

The “PhSO₂CF₂Cu” reagent (from PhSO₂CF₂H) reacts with arylboronic acids, which represents a convenient method for the introduction of the CF₂ moiety into aromatics.

Palladium-catalyzed C-H ethoxycarbonyldifluoromethylation of electron-rich heteroarenes

The first Pd-catalyzed C-H ethoxycarbonyldifluoromethylation with BrCF2CO2Et has been developed. The use of a bidentate phosphine ligand (Xantphos) is critical for the reaction to occur. A variety of electron-rich heteroarenes, including indoles, furans, thiophenes, and pyrroles, can be ethoxycarbonyldifluoromethylated in moderate to excellent yields. The reactions take place at the C-H bonds adjacent to the heteroatoms with high regioselectivity. This method provides a new protocol for the introduction of difuoroalkyl groups into electron-rich heteroarenes.

Direct gem-difluoromethylenation of sp3-hybridized carbon center through copper-mediated radical/radical cross-coupling for the construction of a CH2–CF2 linkage

An efficient gem-difluoromethylenation of benzyl bromides through copper-mediated direct radical/radical C–C cross-coupling has been developed for the construction of CH₂–CF₂ linkage.

Fluorination of 2-substituted benzo[b]furans with Selectfluor™

An efficient protocol was developed to access 3-fluoro-2-hydroxy-2-substituted benzo[b]furans with Selectfluor™ as the fluorinating reagent in MeCN and water. By utilizing SOCl₂/Py as the dehydrating agent, the compounds above were readily converted to 3-fluorinated, 2-substituted benzo[b]furans in high yields.