Electrochemical Difunctionalization of gem-Difluoroalkenes: A Metal-Free Synthesis of α-Difluoro(alkoxyl/azolated) Methylated Ethers

FON: An Innovative Fluorinated Group via Hydroetherification-Type Reactivity

An efficient strategy for preparing the novel O-difluoroalkylhydroxylamine fluorinated functional group, coined FON, is reported. This analogue of medicinally important β-phenethyl ether scaffolds in uniting gem-difluoro and N-O moieties is synthesized in one step via chemo- and regioselectivity metal-free hydroetherification-type additions. As shown, this unique mode of reactivity is realized for a diverse substrate scope and applied to gram-scale synthesis and site-selective deuterium incorporation. Lastly, a mechanistic understanding with implications in Brønsted acid catalysis is offered.

Electrochemical Oxidative Cascade Cyclization of Alkenyl Alcohols with External Nucleophiles to Access Amino- and Hydroxy-Functionalized O-Heterocycles

A convenient electrochemical oxidative cascade cyclization of alkenes equipped with pendant alcohols with general nucleophiles was developed. Using readily available diarylmethanimine and carboxylic acids as nucleophilic sources, a broad range of internal alkene and terminal alkene substrates could produce RCO2- and Ar2CN-functionalized O-heterocycles in moderate to high yields without the requirement for external oxidants and metals. These resulting products can subsequently be hydrolyzed to yield valuable NH2- and OH-functionalized tetrahydrofurans and tetrahydropyranes under mild conditions. Importantly, the efficient conversion of secondary alcohol products to amines with complete inversion of configuration enhances the methodology, enabling the construction of 2-aryl-3-amino tetrahydrofuran with high and complementary diastereoselectivity.

PdII/CuI-Cocatalyzed Radical Arylation of gem-Difluoroalkenes Using Arylsulfonyl Chlorides

A PdII/CuI-cocatalyzed arylation of gem-difluoroalkenes with arylsulfonyl chlorides, affording various defluorinative arylation/1,2-difunctionalized products, was developed. The interception of aryl radicals generated from the reduction of arylsulfonyl chlorides delivers some hypervalent Pd species, which present high reactivities and chemoselectivities toward the defluorinative arylation product formation. Besides, the nature of the electron-deficient Pd metal center is more prone to reductive elimination under acidic conditions, providing an opportunity to explore new reactivates of fluorinated alkenes into more elaborate substructures.

Electrochemically Enabled Hydroxyphosphorylation of 1,3-Enynes to Access Phosphinyl-Substituted Propargyl Alcohols

Catalytic difunctionalization with the direct activation of (O)P-H bonds has been recently established as a potentially robust platform to generate valuable organophosphorus compounds. In terms of 1,3-enynes, despite of the various catalytic methods developed for hydrophosphorylation, the radical-mediated hetero-functionalization of two different atoms has been less explored. In this study, we disclosed an electrochemically induced hydroxyphosphorylation of 1,3-enynes for the construction of phosphinyl-substituted propargyl alcohols. The system involves the direct activation of both arylphosphine oxides and oxygen in ambient air with no external metal or additive needed. The use of electrochemistry ensures the regioselective, atom-economic and eco-friendly for the difunctionalization process. This strategy highlights the advantages of mild reaction conditions, readily available starting materials and broad substrate scope, showing its practical synthetic value in organic synthesis.

Electrochemically Direct Fluorination Functionalization of Styrenes with Different Fluorine Source: Access to Fluoroalkyl Derivatives

A mild protocol for electrochemically oxidative fluorodifunctionalization of styrenes has been demonstrated. The reaction proceeds under metal, external oxidant, and catalyst free conditions, allowing tunable access to a wide variety of synthetically useful fluoroalkyl derivatives, such as β-fluorosulfone/fluoromethyl, fluorothiocyanation, and vinylsulfonyl derivatives. Moreover, CsF was shown to be the proper fluorine source for this electrochemical fluorodifunctionalization transformation.

Synthesis of Sterically Hindered Dialkyl Ethers via Palladium-Catalyzed Fluoro-alkoxylation of gem-Difluoroalkenes

Organofluorine compounds are of high value in medicinal and agricultural chemistry. Herein, we report a palladium-catalyzed fluoro-alkoxylation of gem-difluoroalkenes for the synthesis of much more challenging sterically hindered ethers. This reaction represents a direct synthesis method for α-trifluoromethyl ethers with a broad functional group tolerance and excellent regioselectivity. This system employs N-fluorobenzenesulfonimide (NFSI) as an electrophilic fluorine source and alcohols as nucleophilic donors, including but not limited to sterically hindered tert-substituted alcohols.

Electrochemical Fluorination Functionalization of gem-Difluoroalkenes with CsF as a Fluorine Source: Access to Fluoroalkyl Building Blocks

Using easily handled CsF as a fluorine source, an electrochemically metal-free protocol for chemo- and regioselective synthesis of various types of long-chain perfluoroalkyl aromatics with gem-difluoroalkene as a substrate and an alcohol or azole as an additional nucleophile was developed. The eletrochemical transformation could tolerate several functional groups, such as halogens, cyanos, benzyls, and heterocycles, and is amenable to gram-scale. The application of this electrochemical method in radiofluorination was also tested.

Synthesis of α-Trifluoromethyl Alkynes through Fluoroalkynylation of gem-Difluoroalkenes

A trifluoromethylalkynylation reaction of gem-difluoroalkenes with alkynyl sulfoxide by photoredox radical addition with good functional group tolerance in moderate to high yields, is developed for the synthesis of α-trifluoromethyl alkyne. This reaction features simple operation and inexpensive raw materials and provides an expeditious route to synthesize biologically relevant fluorine-containing alkynyl compounds with diverse structural skeletons.

Photoredox-Catalyzed gem-Difluoromethylenation of Aliphatic Alcohols with 1,1-Difluoroalkenes to Access α,α-Difluoromethylene Ethers

A switchable synthesis of alcohols and ketones bearing a CF2-OR scaffold using visible-light promotion is described. The method of PDI catalysis is characterized by its ease of operation, broad substrate scopes, and the ability to switch between desired products without the need for transition metal catalysts. The addition or absence of a base plays a key role in controlling the synthesis of the major desired products.