Silver-Promoted Radical Cascade Aryldifluoromethylation/Cyclization of 2-Allyloxybenzaldehydes for the Synthesis of 3-Aryldifluoromethyl-Containing Chroman-4-one Derivatives

A convenient silver-promoted radical cascade aryldifluoromethylation/cyclization of 2-allyloxybenzaldehydes has been developed. Experimental studies disclosed that the addition of aryldifluoromethyl radicals in situ produced from easily accessible gem-difluoroarylacetic acids to unactivated double bonds in 2-allyloxybenzaldehyde was an effective route to access a series of 3-aryldifluoromethyl-containing chroman-4-one derivatives in moderate to good yields under mild reaction conditions.

Remote Selective Decarboxylative Difluoroarylmethylation of 8-Aminoquinolines under Transition Metal-Free Conditions

A facile transition metal-free decarboxylative C4 selective C-H difluoroarylmethylation of 8-aminoquinolines has been developed. This strategy proceeds under simple aqueous conditions and displays a broad substrate scope and excellent functional...

Difluoromethylation of Heterocycles via a Radical Process

Difluoromethylation is of prime importance for its applicability in functionalizing diverse fluorine-containing heterocycles, which are core moieties of various biologically and pharmacologically active ingredients. Due to their significant biological and...

Recent Advances in Transition-Metal-Catalyzed Selective C–H Alkoxycarbonyldifluoromethylation Reactions of Aromatic Substrates

Fluorine is well-known as a very special element. Approximately 30% of agrochemicals and 20% of all drugs contain fluorine; most of those compounds have unique functions in biochemistry, pharmacy, and bioscience and those containing alkoxycarbonyldifluoromethyl functional groups often have irreplaceable roles. Therefore, the selective introduction of alkoxycarbonyldifluoromethylated functional groups into various aromatic substrates has significant practical application. This review describes recent advances in selective alkoxycarbonyldifluoromethylation of aromatic substrates by using different catalytic strategies (cyclometalated ruthenium complex, transient regulating and visible-light-induced strategies).

1 Introduction

2 para-C–H Alkoxycarbonyldifluoromethylation of Aromatic Derivatives

2.1 Ruthenium Catalysis

2.2 Palladium Catalysis

2.3 Visible-Light Catalysis

2.4 Iron Catalysis

3 meta-C–H Alkoxycarbonyldifluoromethylation of Aromatic Derivatives

3.1 Ruthenium Catalysis

3.2 Palladium Catalysis

4 The Influence of Transition Metals and Directing Groups on Site Selectivity of Alkoxycarbonyldifluoromethylation

4.1 The Influence of Directing Groups on the Site Selectivity of Alkoxycarbonyldifluoromethylation

4.2 The Influence of Transition Metals on the Site Selectivity of Alkoxycarbonyldifluoromethylation

5 Conclusions

Visible-light mediated stereospecific C(sp2)-H difluoroalkylation of (Z)-aldoximes

A visible light mediated stereospecific C(sp²)-H difluoroalkylation of (Z)-aldoximes to (E)-difluoroalkylated ketoximes has been described. In this reaction, (hetero)-aromatic and aliphatic difluoroalkylated ketoximes could be obtained with the retention of the configuration of the starting aldoximes. A preliminary mechanism study showed that a difluoromethyl radical via an SET pathway was involved.

Metal-free, oxidative decarboxylation of aryldifluoroacetic acid with the formation of the ArS-CF2 bond

A metal-free, oxidative decarboxylative reaction of aryldifluoroacetic acids with diaryl disulfides or thiols under mild reaction conditions has been developed. This is an efficient and straightforward radical cross-coupling method for the synthesis of diverse aryldifluoromethylthio ethers in moderate to excellent yields.

Wonderful fusion of organofluorine chemistry and decarboxylation strategy

Decarboxylation strategy has been emerging as a powerful tool for the synthesis of fluorine-containing organic compounds that play important roles in various fields such as pharmaceuticals, agrochemicals, and materials science. Considerable progress in decarboxylation has been made over the past decade towards the construction of diverse valuable fluorinated fine chemicals for which the fluorinated part can be brought in two ways. The first way is described as the reaction of non-fluorinated carboxylic acids (and their derivatives) with fluorinating reagents, as well as fluorine-containing building blocks. The second way is dedicated to the exploration and the use of fluorine-containing carboxylic acids (and their derivatives) in decarboxylative transformations. This review aims to provide a comprehensive summary of the development and applications of decarboxylative radical, nucleophilic and cross-coupling strategies in organofluorine chemistry.

Silver-catalyzed decarboxylative radical allylation of α,α-difluoroarylacetic acids for the construction of CF2-allyl bonds

An efficient silver-catalyzed method of decarboxylative radical allylation of α,α-difluoroarylacetic acids to build CF2-allyl bonds has been developed. Using allylsulfone as an allyl donor, α,α-difluorine substituted arylacetic acids bearing various functional groups are successfully allylated to access a series of 3-(α,α-difluorobenzyl)-1-propylene compounds in moderate to excellent yields in aqueous CH3CN solution under the mild conditions. Experimental studies disclosed that the α-fluorine substitution of arylacetic acid has a great influence on free radical activity and reactivity.

Ruthenium-Catalyzed PIII-Directed Remote ε-C-H Alkylation of Phosphines

The ruthenium-catalyzed remote ε-C-H alkylation of phosphines with tertiary alkyl halides has been developed. This novel P^III-directed C-H activation strategy tolerated various functional groups and delivered a wide variety of modified phosphines with excellent meta-site selectivity. Preliminary mechanistic studies indicated that a P^III-assisted ortho-cyclometalation/remote σ-activation pathway might be involved in this methodology.

Modern approaches towards the synthesis of geminal difluoroalkyl groups

This review will cover the importance of and most recent approaches toward geminal difluoroalkyl groups. Transition metal-mediated, photochemical, organocatalytic, and other methods as well as their mechanistic implications will be discussed, with special emphasis on applications to biologically-relevant compounds.

Synthetic applications of α,α-difluoroarylacetic acids and salts via decarboxylative functionalization

α,α-Difluoroarylacetic acids are stable, inexpensive and readily available building blocks which can be used to access various difluoromethylated aryl motifs via decarboxylative functionalization for the formation of carbon–carbon and carbon-heteroatom (F, O, S) bonds.

Silver-catalyzed decarboxylative radical relay difluoroalkylation–carbocyclization: convenient access to CF2-containing quinolinones

A practical Ag-catalyzed formal decarboxylation and radical difluoroalkylation–carbocyclization–hydrolysis route is established to construct a series of structurally diverse CF2-containing N-heterocycles.

Difluoroisoxazolacetophenone: A Difluoroalkylation Reagent for Organocatalytic Vinylogous Nitroaldol Reactions of 1,2-Diketones

Difluoroisoxazolacetophenone (DFIO) is developed as a new difluoroalkylation reagent that can be easily prepared from inexpensive starting materials. In situ remote C-C bond cleavage of DFIO affords γ,γ-difluoroisoxazole nitronate that undergoes base-catalyzed vinylogous nitroaldol additions to isatins, benzothiophene-2,3-dione, unsaturated-α-ketoesters, and cyclic 1,2-diketones. This organocatalytic debenzoate vinylogous nitroaldol reaction provides a new and mild approach for the preparation of various difluoroisoxazole-substituted 3-hydroxy-2-oxindoles.

Fe(III)-Catalyzed Decarboxylative C3-Difluoroarylmethylation of Coumarins with α,α-Difluoroarylacetic Acids

A facile Fe(III)-catalyzed oxidative decarboxylative radical coupling reaction of α,α-difluoroarylacetic acids with coumarins has been developed. This transformation, which provides a series of C-3 difluoroarylmethylated coumarins containing various functional groups in moderate-to-good yields, features easily accessible starting materials and operational simplicity.

Photoinitiated decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-ones with potassium 2,2-difluoro-2-arylacetates in water

An efficient and green strategy for the preparation of C3-difluoroarylmethylated quinoxalin-2(1H)-one via a visible-light-induced decarboxylative C3-difluoroarylmethylation of quinoxalin-2(1H)-one with potassium 2,2-difluoro-2-arylacetate in water at room temperature was developed. This photoinduced reaction generated the desired products in good yields under simple and mild conditions.

Silver-Catalyzed Decarboxylative Allylation of Difluoroarylacetic Acids with Allyl Sulfones in Water

A practical silver-catalyzed decarboxylative allylation of α,α-difluoroarylacetic acids with allyl sulfones is described, which provides a variety of β,β-difluorinated alkenes in good yields. Notably, the reaction proceeds smoothly in water with good functional group tolerance. The practicality and synthetic value of this process was demonstrated by scaled-up experiment and elaboration of the products via reduction or Heck reaction. Primary mechanism investigations suggest that a radical process might be involved.

Ag-Catalyzed minisci C–H difluoromethylarylation of N-heteroarenes

A mild silver-catalyzed decarboxylative C–H difluoromethylarylation of electron-deficient N-heteroarenes.

Visible-Light-Induced para-Selective C(sp2)-H Difluoroalkylation of Diverse (Hetero)aromatic Carbonyls

An efficient visible-light-induced para-selective C(sp²)-H difluoroalkylation of diverse electron-deficient (hetero)aromatic carbonyls (aldehydes and ketones) at ambient temperature has been developed by employing Ir(ppy)₃ as the catalyst and 1,10-phenanthroline as the additive. This protocol was highlighted by its wide substrate scope, high regioselectivity, low catalyst usage, and operational simplicity.

Cascade alkylation and deuteration with aryl iodides via Pd/norbornene catalysis: an efficient method for the synthesis of congested deuterium-labeled arenes

An efficient approach for synthesizing congested deuterium-labeled arenes via cascade alkylation and deuteration with aryl iodides has been disclosed.