Stereoselective synthesis of β-fluoroenyne by the reaction of gem -difluoroalkenes with terminal alkynes

Photoredox-Catalyzed Sequential Decarboxylative/Defluorinative Aminoalkylation of CF3-Alkenes with N-Arylglycines

A photoredox-catalyzed sequential decarboxylative/defluorinative aminoalkylation of CF3-alkenes with N-arylglycines is described. This metal-free and redox-neutral protocol provided efficient access to the monofluoroalkenyl-1,5-diamines in good yields with excellent functional group compatibility. Mechanistic studies revealed that the reaction proceeds via a radical pathway with the gem-difluoroalkenyl amine as an intermediate.

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.

Electrochemical Synthesis of gem-Difluoro- and γ-Fluoro-Allyl Boronates and Silanes

The electrochemical synthesis of fluorinated allyl silanes and boronates was disclosed. The addition of electrogenerated boryl or silyl radicals onto many α-trifluoromethyl or α-difluoromethylstyrenes in an undivided cell allowed the formation of a large panel of synthetically useful gem-difluoro and γ-fluoroallyl boronates and silanes (64 examples, from 31 % to 95 % yield). In addition, a scale up of the reactions under continuous flow was showcased using an electrochemical reactor with promising volumetric productivity (688 g.L-1 .h-1 and 496 g.L-1 .h-1 ). Moreover, the synthetic utility of these building blocks was highlighted through versatile transformations. Finally, plausible reaction mechanisms were suggested to explain the formation of the products.

Divergent Synthesis of Fluorinated Alkenes, Allenes, and Enynes via Reaction of 2-Trifluoromethyl-1,3-enynes with Carbon Nucleophiles

Herein, inorganic base K₃PO₄ promoted divergent synthesis of CF₃-substituted allenes, cyclopentenes, alkynes, and fluorinated enynes via regioselective nucleophilic addition of carbon nucleophiles to 2-trifluoromethyl-1,3-enynes was developed. With the choice of different carbon nucleophiles, various fluorinated compounds could be obtained under K₃PO₄/DMF reaction system. When malononitriles were used as nucleophiles, CF₃-substituted allenes, cyclopentenes, and alkynes could be obtained, respectively. By using 1,3-dicarbonyl compounds as nucleophiles, ring-monofluorinated 4H-pyrans could be prepared, and 1,1-difluoro-1,3-enynes could be furnished with the participation of diethyl malonate. Moreover, these five kinds of fluorinated allenes, alkenes, and enynes are valuable building blocks.

Nucleophilic Vinylic Substitution (SNV) of Trisubstituted Monofluoroalkenes for the Synthesis of Stereodefined Trisubstituted Alkenes and Divinyl Ethers

We herein describe a nucleophilic vinylic substitution (S_NV) of trisubstituted monofluoroalkenes with excellent stereocontrol (d.r. > 99:1). Starting from (E)-β-monofluoroacrylates, various trisubstituted (E)-alkenes containing O/N/S-substituent groups at the vinylic position can be obtained under simple conditions. Furthermore, (E,E)-divinyl ethers can be generated through dimerization of the monofluoroalkenes, triggered by adventitious water in the reaction mixture.

One-pot method for the synthesis of 1-aryl-2-aminoalkanol derivatives from the corresponding amides or nitriles

We have identified a novel one-pot method for the synthesis of β-amino alcohols, which is based on C–H bond hydroxylation at the benzylic α-carbon atom with a subsequent nitrile or amide functional group reduction. This cascade process uses molecular oxygen as an oxidant and sodium bis(2-methoxyethoxy)aluminum hydride as a reductant. The substrate scope was examined on 30 entries and, although the respective products were provided in moderate yields only, the above simple protocol may serve as a direct and powerful entry to the sterically congested 1,2-amino alcohols that are difficult to prepare by other routes. The plausible mechanistic rationale for the observed results is given and the reaction was applied to a synthesis of a potentially bioactive target.

A one-pot method for β-amino alcohol synthesis based on α-hydroxylation and subsequent amide or nitrile functional group reduction has been identified and examined.

Stereoselective Synthesis of Terminal Monofluoroalkenes from Trifluoromethylated Alkenes

Herein we report the hydrodefluorination reaction of trifluoromethylated alkenes to access terminal monofluoroalkenes. The use of LiAlH₄ allowed the stereoselective synthesis of the terminal monofluoroalkenes in good to excellent yields with good to excellent diastereoselectivities. Mechanistic studies suggested a hydroalumination reaction followed by a stereoselective fluoride elimination.

Recent advances in three-component difunctionalization of gem-difluoroalkenes

Three-component difunctionalization of gem-difluoroalkenes via the generation and transformation of a α-fluoroalkylated carbanion, a carbon–metal species, a radical, and a carbocation intermediate.

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.

Domino C-F Bond Activation of the CF3 Group: Synthesis of Fluorinated Dibenzo[a,c][7]annulenes from 2-(Trifluoromethyl)-1-alkenes and 2,2'-Diceriobiaryls

The construction of ring-fluorinated seven-membered carbocycles was readily achieved via the domino S_N2'-type/S_NV reaction between 2-(trifluoromethyl)-1-alkenes and 1,4-carbodianions. The S_N2'-type reaction of 2-(trifluoromethyl)-1-alkenes with 2,2'-diceriobiaryls generated the intermediary 1,1-difluoro-1-alkenes bearing a monoceriobiaryl moiety, which in turn underwent intramolecular S_NV reaction to afford fluorinated 5H-dibenzo[a,c][7]annulenes.

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.

One-pot syntheses of N-(α-fluorovinyl)azole derivatives from N-(diphenylmethylene)-2,2,2-trifluoroethanamine

N-(Diphenylmethylene)-2,2,2-trifluoroethanamine acts as a versatile fluorine-containing building block, and from which N-(α-fluorovinyl)azole derivatives were prepared in a one-pot process.

Synthesis of fluorovinyl aryl ethers by a three-component reaction of gem-difluoroalkenes with arylboronic acids and oxygen

An efficient three-component reaction for the synthesis of fluorovinyl aryl ethers from gem-difluoroalkenes, arylboronic acids and oxygen is described.

Base-mediated direct fluoroalkenylation of 2-phenyl-1,3,4-oxadiazole, benzothiazole and benzoxazole with gem-difluoroalkenes

Direct α-fluorovinylation of 2-phenyl-1,3,4-oxadiazole, benzothiazole and benzoxazole with gem-difluoroalkenes under the assistance of KHMDS or NaH at room temperature was developed.

Base-promoted direct and highly selective alkynylation of electron-deficient octafluorotoluene

Experimental and theoretical studies are reported on the base-promoted direct alkynylation of octafluorotoluene via highly selective C–F bond cleavage.

Nickel-catalyzed Suzuki–Miyaura type cross-coupling reactions of (2,2-difluorovinyl)benzene derivatives with arylboronic acids

An unprecedented highly stereoselective example of nickel-catalyzed Suzuki–Miyaura type cross-coupling reactions of (2,2-difluorovinyl)benzene derivatives with arylboronic acids was developed.

Synthesis of monofluoroalkenes through selective hydrodefluorination of gem-difluoroalkenes with Red-Al®

A practical approach for the selective hydrodefluorination of gem-difluoroalkenes using Red-Al® as reductant at room temperature in CH₂Cl₂ was reported. Monofluoroalkenes were obtained in moderate to high yields with good E-selectivity.