Synthesis of Difluorinated Enynes through Sonogashira-Type Coupling

Gold-Catalyzed Regio- and Stereoselective α-Acyloxy-β-Alkynylation of Ynol Ethers

Enol esters and conjugated enynes are valuable structural motifs for synthetic chemistry and material sciences. Herein, the synthesis of tetra-substituted enol ester 2-iodobenzoate derivatives was achieved in good yields at room temperature through a gold-catalyzed acyloxyalkynylation of sensitive ynol ethers with ethynylbenziodoxolones (EBXs), the latter acting as bifunctional reactants. The conversion is highly regioselective with a broad substrate scope. Mechanistically, an Au(III) species is the key intermediate of an Au(I)/Au(III) redox cycle. The reaction is synthetically useful and can easily be scaled up to gram scale.

Diverse reactivity of the gem-difluorovinyl iodonium salt for direct incorporation of the difluoroethylene group into N- and O-nucleophiles

The synthesis of gem-difluoroethylene compounds remains a difficult task in organic synthesis. Here, the direct difluoroethylation reactions of N- and O-nucleophiles including amides and acids were realized with a hypervalent iodine reagent: gem-difluorovinyl iodonium salt (DFVI). The reactions were accomplished via a neighbouring group rearrangement. The gem-difluorovinyl iodonium salt was found to display diverse reactivity due to its unique electronic effect and was applied to the incorporation of difluoroethylene group, including difluorovinylation of carboxylic acids, difluorovinylation and 1,3-cyclic fluorovinylation of amides and 1,1-cyclic difluoroethylation of amines.

Synthesis of gem-Difluorinated 1,3-Dienes via Synergistic Cu/Pd-Catalyzed Borodifluorovinylation of Alkynes

gem-Difluoroalkenes (=CF₂), which normally act as metabolically stable bioisosteres for carbonyl groups (C═O), are widely applied in agrochemicals and pharmaceuticals and are also used as building blocks in organic synthesis. Herein, an example of Cu/Pd-catalyzed borodifluorovinylation was achieved using alkynes, difluoroethylene bromide, and B₂pin₂ as chemical feedstocks, providing the corresponding conjugated gem-difluoroalkene scaffold with good functional group compatibility. Moreover, an array of fluorinated synthons can be obtained through further transformations.

Regio- and Stereoselective Addition to gem-Difluorinated Ene-Ynamides: Access to Stereodefined Fluorinated Dienes

The first synthesis of gem-difluorinated ene-ynamides is presented via deprotonation of trifluoromethylated N-allenamides and δ extrusion of fluorine. These highly reactive building blocks, owing to their dual functional groups, offer a unique entry to difluorinated dienes and to stereodefined, monofluoro-substituted dienes. Stereoselective addition to the ynamide moiety led to difluorinated dienes. A stereocontrolled domino δ elimination reaction followed by an addition/elimination sequence from trifluoromethylated N-allenamides provided exclusively stereodefined monofluorinated ene-ynamides.

gem-Difluorovinylation of alkynyl bromoarenes via dual nickel-/palladium-catalyzed cross-electrophile coupling

A dual nickel-/palladium-catalyzed gem-difluorovinylation of alkynyl bromoarenes is presented. This method proceeds smoothly to afford various dihydrobenzofuran compounds containing gem-difluorovinyl fragments with excellent stereoselectivities.

Preparation of (E)-1,3-Enyne Derivatives through Palladium Catalyzed Hydroalkynylation of Allenes

A general and efficient palladium catalyzed hydroalkynylation of allenes was developed to produce synthetically versatile (E)-1,3-enyne derivatives with high regio- and stereoselectivity. This catalytic system proceeded under mild conditions and was compatible with a broad range of substrates, especially for allenes without electron-bias groups. This work further broadens the synthetic potential of these scaffolds in organic synthesis and medicinal chemistry.

Simple Synthesis of Fluorinated Ene-Ynes via In Situ Generation of Allenes

Fluorination of small molecules is a key route toward modulating reactivity and bioactivity. The 1,3 ene-yne functionality is an important synthon towards complex products, as well as a common functionality in biologically active molecules. Here, we present a new synthetic route towards fluorinated ene-ynes from simple starting materials. We employ gas chromatography-mass spectrometry analysis to probe the sequential eliminations necessary for this transformation and observe an allene intermediate. The ene-yne products are sufficiently fluorous to enable purification via fluorous extraction. This methodology will allow facile access to functional, fluorous ene-ynes.

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.

The dual-catalyzed boryldifluoroallylation of alkynes: an efficient method for the synthesis of skipped gem-difluorodienes

The Cu/Pd-catalyzed boryldifluoroallylation of alkynes was achieved, providing the skipped gem-difluorodiene scaffolds with high regio- and stereoselectivity. An array of synthetic building blocks can be obtained via further transformations.

Palladium-catalyzed decarboxylative gem-selective addition of alkynoic acids to terminal alkynes

Alkynoic acids added to terminal alkynes to give gem-1,3-enynes with high selectivity and good yields. In addition, the reaction of alkynoic acids with propiolic acid provided the corresponding gem-1,3-enynes via double decarboxylation.

Cp*Rh(III)-Catalyzed C-H Bond Difluorovinylation of Indoles with α,α-Difluorovinyl Tosylate

Unprecedented Rh(III)-catalyzed C-H bond difluorovinylation of indoles has been successfully developed, and this method provided an example of direct difluorovinylation reaction through C-H bond activation which was rarely reported. In this context, N-ethoxycarbamoyl served as the directing group and 2,2-difluorovinyl tosylates were used for the construction of difluorovinyl-substituted indoles. This method provided a practical strategy for difluorovinylation of indoles with moderate to good yields and is characterized by the broad synthetic utility, mild conditions, and high efficiency.

Synthesis of difluoromethylated enynes by the reaction of α-(trifluoromethyl)styrenes with terminal alkynes

A novel and efficient method for the synthesis of difluoromethylated enynes by the reaction of α-(trifluoromethyl)styrenes with terminal alkynes with the assistance of NaOtBu was described. The mechanism of the reaction might involve the SN2' reaction of α-(trifluoromethyl)styrenes and a subsequent 1,3-H shift. Isomerization (E → Z) of 1-difluoromethyl-1,3-enynes in the presence of ZrCl4 was also developed.

General Synthesis of Alkenyl Sulfides by Palladium-Catalyzed Thioetherification of Alkenyl Halides and Tosylates

The cross-coupling reaction of alkenyl bromides with thiols catalyzed by palladium complexes derived from inexpensive dppf ligand is reported. These reactions occur under low catalyst loading and in high yields and display wide scope, including the coupling of bulky thiols and trisubstituted bromoolefins, and functional group tolerance. In addition, the thioetherification of less reactive chloroalkenes and, for the first time, alkenyl tosylates was accomplished using a catalyst generated from CyPF tBu alkylbisphosphine ligand.

Rh-Catalyzed C–H bond alkylation of indoles with α,α-difluorovinyl tosylate via indolyl group migration

An unprecedented C–H alkylation of indoles was achieved with α,α-difluorovinyl tosylate through an indolyl group shift process enabled by fluorine substituents.

Palladium-Catalyzed Decarboxylative Coupling of Alkynyl Carboxylic Acids with Aryl Tosylates

Decarboxylative coupling reactions of alkynyl carboxylic acids with aryl tosylates were developed in the presence of a palladium catalyst. Among the commercially available phosphine ligands, only 1-dicyclohexylphosphino-2-(di-tert-butylphosphino-ethyl)ferrocene (CyPF-tBu) showed good reactivity. The reaction took place smoothly and gave the decarboxylative coupled products in moderate to good yields. This demonstrates the excellent functional group tolerance toward alkyl, alkoxy, fluoro, thiophenyl, ester, and ketone groups. In addition, alkyl-substituted propiolic acids, such as octynoic and hexynoic acids, were coupled with phenyl tosylate to provide the desired products. We found that the electronic properties of the substituents on the phenyl ring in arylpropiolic acids are an important factor. The order of reactivity was found to be aryl iodide > aryl bromide > aryl tosylate > aryl chloride. However, aryl chloride-bearing electron-withdrawing groups showed higher reactivity than those bearing aryl tosylates.